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El desarrollo del mapa genético de yuca ha facilitado las investigaciones en la búsqueda de genes asociados con resistencias a plagas que disminuyen producción y calidad. Las herramientas moleculares como los marcadores facilitan la identificación de los genes que dominan la resistencia a plagas como el caso del ácaro verde (AVY) Mononychellus tanajoa en yuca (Manihot esculenta). Inicialmente se identificaron los individuos de poblaciones retrocruces (BC1) progenie de las cuatro familias denominadas CW. De estos BC1 se seleccionaron individuos resistentes y susceptibles teniendo en cuenta la escala de daño reportada por el programa de Entomología del Centro Internacional de Agricultura Tropical. Se evaluaron 500 cebadores microsatélites mediante análisis de grupos segregantes (BSA), cinco de ellos expresaron polimorfismo y mostraron diferencias significativas entre los parentales, los grupos contrastantes y tres cebadores SSRY 11 SSRY 346 y NS 1099. Al realizar los análisis estadísticos correspondientes se encontró que los cebadores NS 1099 y NS 346 presentaron asociación entre estos y los individuos de las familias CW 67 CW 66 y CW 67 respectivamente. Las familias CW67 Y CW66 presentaron la mejor asociación con los marcadores y éstos presentaron mayor asociación con la característica de resistencia al daño causado por M. tanajoa en la población segregante (cebador NS1099 familias CW66 0.56 CW67 0.61 y NS346 familia CW67 0.61). Con base en estos resultados se puede sugerir la utilización de microsatélites en análisis posteriores en otras poblaciones para lograr la identificación de algunas regiones cromosómicas que confieren la resistencia al ácaro verde de la yuca.

Cassava is attacked by a complex of arthropod pests across the tropical regions of the world where the crop is grown. Root yield losses have been recorded for several pests, including mites, mealybugs, whiteflies, hornworm, lacebugs, thrips and burrower bugs. Agronomic characteristics such as vegetative propagation, a long growth cycle, drought tolerance, staggered planting dates and intercropping contribute to the considerable diversity of pests that feed on the crop. The dynamics of cassava production are evolving as trends in the food, feed and industrial starch sector are leading to an increased demand for high quality starches. The resulting shift to larger scale production units, expansion of cultivated area and modifications in crop management combined with the effects of climate change, especially warmer temperatures and altered rainfall patterns, affect the occurrence and dynamics of arthropod pests in cassava agro ecosystems. Data is presented to describe the effects of temperature and dry seasons on key pest species. Whiteflies, mites and mealybugs register a suitability increase in the same areas in South America: Northeastern Brazil, Northern Argentina, South-Central Bolivia, and Southwest Peru. In Africa increases are projected in Southeast Africa and Madagascar. In Asia, regions with greater projected suitability for these pest species are Coastal India and Southeast Asia. Future trends and important criteria that will influence the severity and management of key pests are discussed.

The cassava mealybug Phenacoccus herreni (Sternorryncha: Pseudococcidae) is a pest of cassava, Manihot esculenta Crantz (Euphorbiaceae), in South America. Proteins, representing direct gene products, are prime candidates in genetic engineering manipulations for host plant resistance. Jatropha gossypiifolia L. (Euphorbiaceae), a plant species known to contain proteins toxic to insects, exhibited insecticidal properties to P. herreni. The toxic compounds consisting of proteins around 101.02 kDa appeared to be mostly located in the mature leaves. Further studies are needed to identify the proteins and to ensure that they are not toxic to mammals.

Insect pests and plant diseases reduce cassava yields substantially, posing a threat to food security throughout the developing world. While agricultural scientists have recognized these threats, few assessments of the geographic distribution of cassava pests and diseases have been made at the global scale. The goal of this study is to make such an evaluation for four key biotic constraints to cassava production in developing countries: whiteflies, cassava green mites, cassava mosaic disease and cassava brown streak disease. Occurrence records were obtained from laboratory and biodiversity databases and from the scientific literature. These records were then used in ecological niche models to predict the potential distribution of cassava pests and diseases. The distribution maps were cross validated by holding back 20% of the occurrence records. Potential distribution maps were developed by combining the results of the best ecological niche models. Hotspots for potential cassava pest and disease outbreaks include the Mato Grosso in Brazil, northern South America, the African rift valley, the southern tip of India and much of Southeast Asia, where all four biotic constraints show high potential suitability. Our work highlights how potential geographical shifts in infestation hotspots for several cassava biotic constraints will require intensified monitoring, evaluation and research to prevent yield losses and ensure food security.

The levels of resistance in the wild species of cassava, Manihot tristis Muell-Arg. (Malpighiales: Euphorbiaceae), to the whitefly, Aleurotrachelus socialis Bondar (Hemiptera: Alelyrodidae), the most important economic pest in cassava, Manihot esculenta Crantz (Malpighiales: Euphorbiaceae) crops in South America, were estimated under glasshouse conditions. The parameters of the life history of A. socialis were studied on TST-26 and TST-18 accessions of the wild parent and compared with the susceptible (CMC-40) and resistant (MEcu-72) cultivars. The average longevity on the wild accessions (TST-26, 4.1; TST-18, 4.6 days) and oviposition rates (TST-26, 2.0; TST-18, 1.6 eggs/female/2 days) of the A. socialis females were not significantly different from those of MEcu-72 (5.1 days and 3.4 eggs/female/2 days). The longevity and oviposition rates on CMC-40 were highest (11 days and 8.6 eggs/female/2 days). Analyses of the demographic parameters (Ro, r(m); DT) showed a significant impact of the M. tristis accessions on the potential growth of A. socialis. The average survival time of adults that fed on TST-26, TST-18, and MEcu-72 were significantly different from those recorded on the susceptible genotype. Results from this study revealed important levels of resistance to the whitefly A. socialis on the TST-26 and TST-18 accessions due to the marked differences found for longevity and reproduction, which influenced and were consistent with the differences found in the net reproduction rate (Ro), intrinsic growth rate (r(m)) and population doubling time (DT). The combined effect of these parameters indicated that M. tristis accessions were inappropriate hosts for A. socialis.

Aleurotrachelus socialis is one of the most important pests of cassava (Manihot esculenta Crantz) in the Neotropics. In Colombia, high whitefly populations can reduce crop yields by 79%; and although the farmers intensify the use of insecticides, this practice is highly contaminating, costly and leads to the development of resistance in the insect. An alternative for managing whitefly populations is to develop genetically resistant varieties. Wild parents of Manihot are a useful source of genes against pests for the cultivated species of cassava. Based on prior research that showed the existence of moderate-to-high levels of resistance to A. socialis in Manihot flabellifolia, a wild species of cassava, this study was proposed to characterize this new source of resistance, evaluating the biology and demographics of A. socialis on eight accessions of M. flabellifolia, a susceptible check (CMC-40) and a resistant (MEcu72) check. The averages of A. socialis longevity and fecundity on the accessions were not significantly different to MEcu72, but different from CMC-40 (P

Nematodos entomopatógenos (NEP‚s) de los grupos Heterorhabditidae y Steinernematidae son usados como agentes potenciales de control de numerosas plagas subterráneas, encontrándoselos según estudios de su distribución, en diversidad de hábitats a través del mundo. En el mismo interés de control de rizófagos, especialmente las plagas del complejo chisas (Coleoptera: Melolonthidae) y chinche de la viruela Cyrtomenus bergi (Hemiptera: Cydnidae), se realizó una búsqueda e identificación de cepas nativas de NEP‚s, tomando muestras de suelos en Quindío, Risaralda, Caldas y Cauca. Para la extracción de NEP‚s se emplearon larvas trampa de Galleria mellonella (Lepidoptera: Pyralidae); después de comprobar su patogenicidad siguiendo los postulados de Koch, se multiplicaron, almacenaron e identificaron. De las 284 muestras (300 g de suelo c/u) de 15 cultivos, en 23 sitios 17 resultaron positivas para nematodos entomopatógenos y saprófagos. Usando la técnica PCR dos muestras fueron identificadas como Steinernema kraussei Steiner (Rhabditida: Steinernematidae), procedentes de yuca (ex Manihot esculenta L.) de Cauca y Risaralda (ex Inga spp.), constituyéndose en el primer reporte para Colombia.

Los geminivirus del mosaico de la yuca (CMGs) (Geminiviridae, Begomovirus) y su vector la mosca blanca, Bemisia tabaci, ocasionan las mayores pérdidas en el rendimiento de raíces a cultivos de yuca en África y Asia. Evidencias recientes sugieren que B. tabaci representa un complejo de poblaciones indistinguibles morfológicamente con numerosos biotipos. En las Américas, aunque la yuca parece no ser un hospedero conveniente para el polífago biotipo B, se ha postulado que la ausencia de CMGs y daño mecánico están relacionados con la inhabilidad de este biotipo para colonizar eficientemente este cultivo. No obstante, resultados previos han demostrado que su adaptación a yuca, vía hospederos alternos, es un riesgo que debe tenerse siempre en mente. Este estudio tuvo como objetivo principal evaluar el desarrollo y la reproducción del biotipo B de B. tabaci al alimentarse sobre tres genotipos de M. esculenta (MEcu72, CG489-34 y CMC-40). A través de bioensayos bajo condiciones controladas (25 ± 2°C, 70 ± 5 HR. 12L:12O) se evaluó longevidad, fecundidad, supervivencia y parámetros demográficos, mediante tablas de vida. Aunque las longevidades medias para MEcu72, CG489-34 y CMC-40 fueron similares (6,3, 5,07 y 3,9 días, respectivamente), CMC-40 presentó la tasa de oviposición más baja (0,49 huevos/hembra/2días) comparada con MEcu72 (0,89) y CG489-34 (0,86). Con una tasa de supervivencia muy baja (0,03) MEcu72 fue el único genotipo donde el biotipo B completó su desarrollo de huevo a adulto, necesitando 55,1 días. Los resultados son discutidos evaluando el potencial de adaptación de B. tabaci en Sur América sobre genotipos comerciales de yuca.

Las especies silvestres del género Manihot ofrecen una fuente potencial de genes de resistencia para el control de la mayoría de insectos plaga de yuca (Manihot esculenta). Recientemente, esta característica ha sido aprovechada para el desarrollo de variedades resistentes a plagas y enfermedades a través de cruces inter-específicos con especies silvestres de Manihot. Con el objetivo de buscar nuevas fuentes de resistencia en especies de Manihot, se evaluaron y compararon dos especies silvestres brasileras, Manihot flabellifolia y M. peruviana, frente a genotipos comerciales de M. esculenta, para determinar su potencial de resistencia a tres de las principales plagas de yuca en las Américas, Africa y Asia: el ácaro Mononychellus tanajoa, el piojo harinoso (Phenacoccus herreni) y la mosca blanca (Aleurotrachelus socialis). La investigación se realizó en CIAT, Palmira, bajo condiciones controladas (25±5 ºC, 60±10 HR, 12L/D) utilizando una metodología de tamizados y bioensayos asistida por escalas de infestación y daño. Los resultados mostraron que los genotipos de M. flabellifolia (444-002) y M. peruviana (417-003 y 417-005) exhibieron altos niveles de resistencia frente a M. tanajoa y A socialis, mientras, el genotipo de M. flabellifolia (444-002) y M. peruviana (417-003) presentaron niveles intermedios de resistencia a P. herreni. Se discute la importancia de estas fuentes de resistencia a la luz de los programas de conservación de la diversidad y de la resistencia de planta hospedera como un componente del manejo integrado de plagas.

La mosca blanca Aleurotrachelus socialis Bondar (Hemiptera: Aleyrodidae) es una de las plagas más importantes en el cultivo de yuca (Manihot esculenta Crantz) en el Neotrópico. En Colombia, es el principal limitante del cultivo en los departamentos del Cauca, Valle del Cauca y Tolima ocasionando pérdidas en rendimiento en campos experimentales hasta del 79%. En 1995 esta especie ha colonizado e incrementado sus poblaciones en nuevas variedades y áreas donde anterior- mente era una plaga secundaria. Con el objetivo de conocer el potencial de A. socialis para desarrollar poblaciones en nuevos materiales de yuca, se estimaron los parámetros biológicos y los principales estadísticos vitales de este insecto plaga, realizando bioensayos bajo condiciones controladas (25± 2º C, 70±5% HR, 12L:12D) sobre las variedades Chirosa (MCOL 2066), Ica Armenia (HMC1) y CMC 40. Los resultados mostraron que las hembras de A. socialis vivieron más tiempo (6,4 días) sobre el genotipo CMC-40 y presentaron un alto potencial reproductivo (33,8 huevos por hembra). Por el contrario el menor tiempo de desarrollo (32,72 días) se obtuvo en el genotipo HMC1. Los tres genotipos presentaron altas tasas de supervivencia, siendo mayor en HMC1 (89%). El mayor incremento de las poblaciones (rm) se presentó en los genotipos HMC1 (0,167 día) y CMC40 (0,079 día). Los parámetros poblacionales obtenidos constituyen una herramienta básica para elaborar estrategias de control de A. socialis.

Cyrtomenus bergi Froeschner es un fitófago subterráneo importante en cultivos tropicales. Se evaluaron dos cepas comerciales de nemátodos entomopatógenos (nep) (Steinernema feltiae (Filipjev) y Heterorhabditis bacteriophora Poinar) como antagonistas biológicas bajo invernadero (18-28°C y 55-85% humedad relativa). Se utilizaron las concentraciones comerciales recomendadas por la casa commercial E-nema: 1000 y 500 nep/ml de S. feltiae y H. bacteriophora, respectivamente. Estas soluciones se aplicaron en potes de 1,5 dm3 con suelo agrícola y arena (1:1) con 20 individuos de C. bergi (adultos o inmaduros del quinto instar) confinados por pote. Los insectos fueron alimentados con plantas de maní (Arachis hypogaea L.). La tasa de infestación en el chinche y la mortalidad fueron medidas por medio de evaluaciones destructivas a los 15 y 30 días después de infectados (ddi), tres potes por época. Solo los adultos resultaron infectados (P£0,05). Considerando ambas evaluaciones y todas las cepas, se observó la mayor tasa de penetración en S. feltiae (93,9%) comparado con H. bacteriophora (72,1%). En términos de mortalidad, a 15 ddi H. bacteriophora (42,2%) mató a más insectos que S. feltiae (8,6%); sin embargo, a los 30 ddi no se encontraron diferencias entre las dos cepas de nep (ca. 54,3%). Adicionalmente, se observaron nemátodos melanizados, probablemente como respuesta inmunológica de C. bergi al entomopatógeno, donde S. feltiae (37,5%) fue más susceptible que H. bacteriophora (13,1%) a los 30 ddi. Se concluye que solo los chinches adultos son significativamente susceptibles a los entomonemátodos; H. bacteriophora es la cepa más promisoria al obtener las mayores mortalidades en menos tiempo y presentar el menor porcentaje de melanización bajo estas condiciones.

The larvae of some species of Scarabaeidae, known locally as “chisas” (whitegrubs), are important pests in agricultural areas of the Cauca, Colombia. They form a complex consisting of many species belonging to several genera that affect the roots of commercial crops. The objective of the present study was to identify the members of the complex present in two localities (Caldono and Buenos Aires) and collect basic information on their biology, economic importance, and larval morphology. The first of two types of sampling involved sampling adults in light traps installed weekly throughout one year. The second method involved larval collections in plots of cassava, pasture, coffee, and woodland. Each locality was visited once per month and 10 samples per plot were collected on each occasion, with each sample from a quadrants 1 m2 by 15 cm deep, during 1999-2000. Light traps collected 12,512 adults belonging to 45 species and 21 genera of Scarabaeidae within the subfamilies Dynastinae, Melolonthinae,...

Bemisia tabaci is a recognized pest in cassava ( Manihot esculenta ) crops in Asia and Africa, where it transmits the cassava mosaic geminiviruses (CMGs) (family: Geminiviridae , genus: Begomovirus ). A general consensus exists that B. tabaci is a complex of morphologically indistinguishable populations with different biological biotypes. In the Americas, though the polyphagous B. tabaci biotype B appears to feed on cassava, it is postulated that the absence of CMGs is related to the inability of this biotype to colonize this crop effectively. However, its potential adaptation is considered a threat for cassava production in the Neotropics. This study was initiated to verify whether B. tabaci can become gradually adapted to M. esculenta . Trials in rearing chambers were carried out measuring population development of whitefly individuals passed through a series of intermediate hosts, previously selected and based on phylogenetic closeness to Manihot . The capacity of biotype B to adapt gradually to cassava, started on a legume ( Phaseolus vulgaris ), followed on two Euphorbiaceae ( Euphorbia pulcherrima and Jatropha gossypiifolia ) until, finally reaching a commercial cassava variety. B. tabaci female mean longevity on cassava, coming from P. vulgaris , E. pulcherrima and J. gossypiifolia was 3.1, 5.6 and 3.3 days, respectively. The highest oviposition rate (2.6 eggs/female/2 days), the shortest development time (44.4 days) and the highest value of r m (0.48 day −1 ) were for populations coming from J. gossypiifolia , where 27.5% of the individuals coming from this host survived and reproduced on cassava. The importance and potential impact of phylogenetically close plants as intermediate hosts faciliting the adaptation of B. tabaci biotype B to cassava is discussed.

Little is known about the inheritance of agronomic traits in cassava (Manihot esculenta Crantz). The vegetative multiplication of cassava allows cloning of individual genotypes, and separates environmental from genetic variation in the within-family variation. Knowing the magnitude of between- and within-family variation is important for defining breeding strategies and for measuring different components of genetic variances, particularly the seldom-estimated epistasis. A group of nine genotypes, adapted to midaltitude environments, was used for a diallel study. Thirty clones were obtained from every F 1 cross (each clone was represented by six plants), and planted in three replications at two locations. Statistical differences among crosses were found for fresh-root yield, harvest index, root dry-matter content, and reaction to mites (Mononychellus tanajoa Bondar) and to whiteflies (Aleurotrachelus socialis Bondar). General combining ability (GCA) was significant for all traits except fresh-root yield and dry-matter content, and specific combining ability (SCA) was significant for all traits except whitefly damage score. Fresh-root yield was the only trait with significant epistatic effects, which, combined with a large dominance variance, suggested a prevalence of nonadditive effects. The introduction of inbreeding would be one approach for the efficient exploitation of these nonadditive effects found for fresh-root yield. For the remaining traits, epistasis was negligible and current schemes exploiting additive effects may suffice.

Cassava (Manihot esculenta Crantz) is an important commodity for industrial processes in tropical countries as one of the few alternatives to compete with imported maize (Zea mays L.). To maintain this competitiveness, cassava breeding needs to be as efficient as possible. This study provides one of the first attempts to produce quantitative genetic data to aid breeding efficiency, through the analysis of a diallel set among nine parental clones adapted to the midaltitude valleys environment. Thirty clones represented each F 1 cross (with three exceptions). Evaluations were conducted in two contrasting environments with three replications in each location. The specific combining ability (SCA) effects were relatively more important than general combining ability (GCA) effects for root yield. In the case of harvest index, dry matter content (DMC) and plant type architecture GCA effects were about twice as large as those from SCA effects. Reaction to mites (Mononychellus tanajoa Bondar) and white flies (Aleurofrachelus socialis Bondar) (based on single-location data) showed the strongest influence of GCA effects on the expression of a given trait Yield data demonstrates the excellent potential of this crop for the tropical production of starch and source of energy in animal feed that could compete with the international markets.

Abundance of Cyrtomenus bergi Froeschner has been reported regularly under moist and damp conditions. The influence of temperature and soil moisture on development time and mortality of first, third, and fifth instars, longevity and fecundity of C. bergi adult females, as well as hatching time and rate of eggs were determined under laboratory conditions at different temperature and soil moisture levels. Population growth is optimal around 26°C (constant temperature) and a soil moisture regime ranging from moist (field capacity) to wet soil (between field capacity and water saturation). Wet soil (44% gravimetric soil water) promotes high mean fecundity in young adult females, reducing generation time and favoring population growth compared to that seen in moist soil (33.5% gravimetric soil water, field capacity). The lower temperature threshold for development was 14.7°C. Neither egg hatching nor molting from fifth instars to adults occurred above 31°C. The lower soil moisture threshold for immatu...

Cyrtomenus bergi Froeschner (Hemiptera: Cydnidae) is a polyphagous subterranean burrower bug reported on various crops and weeds in the field. Bionomics and population growth statistics of C. bergi while feeding on peanut (Arachis hypogaea L.), pinto peanut (Arachis pintoi, Krapovickas et Gregory), maize (Zea mays L.), sorghum (Sorghum bicolor [L.] Moench), welsh onion (Allium fistulosum L.),and sweet and bitter cassava (Manihot esculenta Crantz) were calculated from development time, survival of immature stages, and reproduction and female longevity under laboratory conditions. Free-choice host plant selection among peanut, maize and sweet cassava was recorded with separate rearings of C. bergi from the different hosts. Optimal performance ofC. bergi as measured by fecundity, survival, and intrinsic rate of population increase occurred on peanut and pinto peanut followed by maize. Sweet cassava, sorghum, and welsh onion were not favorable hosts, and C. bergi was unable to complete its life cycle...

A survey for parasitoids of the whiteflies, Bemisia tuberculata Bondar, Trialeurodes variabilis Quantaince, T. vaporariorum (Westwood), Aleurotrachelus socialis Bondar, Tetraleurodes sp., Aleuroglandulus malangae Russell and Aleurodicus sp., was conducted in 6 cassava growing regions of Colombia and Ecuador. In Colombia, the degree of infestation was predominantly high (>29 whiteflies/cm2) for A. socialis, B. tuberculata and T. variabilis in all cassava growing regions. In Ecuador, levels of infestations were high for Aleurodicus sp., A. socialis, B. tuberculata, Tetraleurodes sp. in the coastal region, and for T. vaporariorum in the Highlands. The parasitoid fauna of the whiteflies appeared to be more diverse in Colombia than in Ecuador. Eleven species of parasitoids representing 5 genera, 4 families and two superfamilies, as well as 1 hyperparasitoid, were collected from the cassava growing regions of Colombia and 4 species were collected from Ecuador. The parasitoids, Amitus macgowni Evans and...

Amblystira machalana Drake (Chinche negro de encaje) es una plaga del follaje de la yuca, que se ha venido observando desde 1985 en diferentes partes de Colombia, Ecuador y Venezuela provocando daños en este cultivo. Varios trabajos se realizaron en el CIAT con el objeto de conocer su ciclo de vida, comportamiento, dinámica de la población y el efecto en la producción debido al ataque de esta plaga. El ciclo de vida se realizó a nivel de laboratorio a 28ºC y 60-70% HR, utilizando cajas de petri de 10 cm de diámetro, infestando hojas con insectos provenientes del campo. Para el comportamiento del insecto, se realizaron evaluaciones a nivel de campo para determinar su fluctuación en diferentes etapas y épocas del cultivo; al mismo tiempo, se realizaron observaciones de la distribución vertical en la planta. Para determinar su importancia económica, se hizo un ensayo en parcelas de campo con diferentes períodos de protección en bloques al azar con tres repeticiones con la variedad MCol 22. Los resultas indicaron que el ciclo de vida del insecto pasa por cinco ínstares ninfales 1:011 una duración promedia total de huevo hasta adulto de 22,3 días. El comportamiento del insecto en condiciones de campo, indicó que es una plaga que puede atacar el cultivo en las épocas secas y lluviosas con preferencia de las últimas y que las poblaciones son más altas en las hojas del tercio medio y bajo de la planta las que elige para alimentarse. De acuerdo con las variedades, sus daños pueden ser severos y reducen la producción de raíces entre 8,1 y 42, 7%, dependiendo de la duración del ataque del insecto.

The hypothesis that cyanogenic potential in cassava is a defense mechanism against arthropod pests is one of the crucial questions relevant to current efforts to reduce or eliminate cyanogenic potential (CNP) in cassava. The generalist arthropod Cyrtomenus bergi, which attacks cassava roots, was used in a bioassay relating oviposition and survival to CNP, concentration of nonglycosidic cyanogens, and linamarase (beta-glycosidase) activity in twelve selfed cassava siblings and their parental clone, which has segregated for different levels of cyanogenesis. Electron microscopic evaluation revealed an intracellular pathway of the stylet of C. bergi in the cassava root tissue to rupture cell walls. This feeding behavior causes cyanogenesis and increased linamarin content in the hemolymph of C. bergi while feeding on a cyanogenic diet. This diet resulted in a significant reduction in oviposition, especially at levels of CNP above 150 ppm (expressed as hydrogen cyanide) on fresh weight basis (or 400 ppm on dry weight basis) in cassava roots. An exponential decline in oviposition was observed with increasing levels of CNP, beginning 12 d after exposure to the cyanogenic diet. Cyanogenic potential and dry matter content showed a positive effect on survival. No relationship was found between concentrations of nonglycosidic cyanogens or linamarase activity in the cassava root and either oviposition or survival. According to our results, there is a significant difference between potentially noncyanogen and high cyanogen clones, but there may not be a significant difference between potentially noncyanogen and low cyanogen clones. Consequently, more frequent outbreaks or higher levels of damage might not be anticipated in potentially noncyanogen cassava clones than that anticipated in low cyanogenic clones. The negative effect of cyanogenesis on oviposition concurrent with a positive effect on survival of this pest is most likely the result of a physiological trade-off between survival and oviposition. The question of whether ovipositional rates could be recovered after a long-term exposure to cyanide remains unanswered.

The two encyrtid endo-parasitoids, Aenasius vexans Kerrich and Acerophagus coccois Smith, are biological control agents of the cassava mealybug, Phenacoccus herreni Cox and Willliams, in Latin America. Parasitoids used as biological control agents are released in agro-ecosystems in which plants are typically attacked by various herbivore species. We studied the effects of a mixed species infestation by cassava mealybug and cassava green mite, Mononychellus tanajoa Bondar, or whitefly, Aleurotrachelus socialis Bondar, on the mealybug pest and its encyrtid parasitoids. Development, distribution and reproduction of the cassava mealybug as well as the post-alighting behavior and reproduction of the two parasitoid species were analyzed in a mixed species infestation as compared to an infestation by cassava mealybug only. Results show that developmental time of cassava mealybug females was altered when an additional herbivore species was feeding on the same plant. The duration of the third larval instar was significantly shorter when cassava green mite was present. In contrast, the duration of this instar was longer when whitefly was present. Reproduction of cassava mealybug was not affected, nor was the ratio of its distribution on the adaxial and the abaxial surface of the cassava leaf. Our findings on altered developmental time of phloem feeding cassava mealybug in mixed species infestations suggest that the desiccation of leaves caused by the cell sap feeding cassava green mite accelerated mealybug development. In contrast, the interaction with the similarly phloem feeding whitefly retarded it. The post-alighting behavior of the specialist parasitoid A. vexans differed between the two mixed species infestations as compared to the infestation with the cassava mealybug only. The preference of females for the adaxial leaf surface observed in the infestation with cassava mealybug only was not found in either of the mixed species infestations. In contrast, the post-alighting behavior of the generalist parasitoid A. coccois was similar in the mixed species infestations as in the infestation by cassava mealybug only. These results indicate a more robust behavior of the generalist, but the altered behavior of the specialist remained without consequences on parasitism rate under the conditions of this study.

Thrips palmi Karny es una plaga importante en varios cultivos, especialmente en hortalizas. El ácaro predador Neoseiulus cucumeris se ha usado con éxito para el control de especies de trips en varios cultivos y Typhlodromalus aripo tiene gran capacidad de consumir trips de yuca. Con el fin de evaluar a N. cucumeris y T. aripo, como controladores potenciales de T. pnlmi, se plantearon los siguientes objetivos: estudiar el efecto del consumo de T. palmi sobre aspectos de la biología de N. cucumeris y T. eripo, en comparación con las presas acarinas Tetranychus urticae y Mononychellus caribbeanae, cuantificar el consumo de los predadores sobre T. palmi y evaluar a N. cucumeris y T. eripo en su respuesta funcional a las densidades l. 3, 5, 10, 20 y 40 larvas de primer ínstar de T. pelmi. Se trabajó en condiciones de laboratorio controladas (25 ± 5ºC, 75 ± 5% de J-IRy 12:12 L:0). El tiempo de desarrollo de N. cucumeris cuando se alimentó de T. palmi y T. urticae fue de 8.9 y 8.5 días. respectivamente y para T. aripo fue de 15.1 y 13.5 con T. palmi y M. caribbeanae, respectivamente. La fecundidad con T. pelmi para N. cucumeris y T. aripo fue de 25.2 y 15.6, respectivamente. El porcentaje de hembras y la longevidad fueron similares con ambos tipos de presa. Un individuo de N. cucumeris consume 65.3 larvas de primer ínstar de T. palmi y L8.7 larvas de segundo instar durante su vida y T. aripo consume 72.9 larvas de primer ínstar y 21.6 de segundo ínstar durante su vida. Las hembras de N. cucurneris y T. aripo presentaron una respuesta funcional de tipo 11, logrando consumir 16 y 18 larvas de primer ínstar de T. palmi en 24 horas, respecti• vamente; respondiendo positivamente a densidades altas del trips.

Para determinar los principales problemas entomológicos que afectan la producción de espárragos en el departamento del Cauca e identificar los artrópodos que podrían estar presentes en el producto final se realizó esta investigación en tres fincas, dos de ellas localizadas en Cajibío y la otra en Tutoró. a una altitud entre 1800 y 1840 msnm, temperatura promedio de 15ºC, HR 83-86%. El cultivo de espárragos en cada una de las fincas estaba divido de acuerdo con su estado de desarrollo. Se seleccio• naron lotes de tres hectáreas de cada estado de desarrollo del cultivo de espárragos, en los cuales se realizaron muestreos al azar con jama y observación directa de adultos y estados inmaduros. Los muestreos se realizaron cada dos semanas durante siete meses. Se colectaron 1.440 individuos, seleccionándose 70 especies de acuerdo con el número y presencia durante el desarrollo del cultivo. Se identificaron 46 especies pertenecientes a 10 órdenes y 20 familias. Los órdenes de mayor abundancia e importancia económica fueron Hemiptera, Coleoptera, Lepidoptera, Homoptera y Thysanoptera. Del orden Lepidoptera se identificaron las especies Paracles severa (Berg.), Copitarsia consueta (Walker) y Spodoptera sp. nr marima (Schaus), como primeros registros encontrados en espárragos en Colombia. También se halló el áfido Myzus persicae (Sulzer), considerándose de gran importancia por ser transmisor de más de 120 virus. Del orden Thysanoptera se identificó la especie Thrips tabaci Lindeman, durante todo el ciclo del cultivo hasta el producto final, siendo necesario aplicar productos químicos para su control. Además se identificaron especies benéficas de los órdenes Díptera, Coleoptera, Hymenoptera como: Pantomona testacea Klung, Humolobus sp. y Campsomeris dorsata (F.). Neuroptera, Chrysoperla externa (Hagen), parasitando y depredando naturalmente algunas de las especies-plaga identificadas. Igualmente se identificaron las especies de plantas más comunes utilizadas como cobertura en las tres fincas.

The influence of cassava Manihot esculenta Crantz grown under condition of water-stress on development and reproduction of the cassava mealybug, Phenacoccus herreni Cox & Williams, and levels of parasitism of three encyrtid parasitoids, Apoanagyrus diversicornis Howard, Aenasius vexans Kerrich, and Acerophagus coccois Smith, were studied in the laboratory. Two cassava cultivars were used: CM 507-37 (drought-tolerant) and CMC 40. A 30 day period of water stress, imposed by reducing the irrigation volume, led to a reduction in shoot development and stomatal conductance of leaves of both cassava genotypes. Phenacoccus herreni development and reproduction were favoured by cassava under water shortage. Parasitism decreased and water stress appeared to enhance the encapsulation of parasitoid eggs or larvae by the mealybug. In the case of the parasitoid A. diversicornis, there was a decrease in size of female progeny, suggesting a lower fitness in this species on cassava plants under water stress. All results indicated that cassava grown under low water availability favoured P. herreni development and reproduction, and affected the success of parasitism and, depending on the species, parasitoid development. The drought-tolerance characteristic of cassava genotypes and parasitoid species most suitable for controlling P. herreni in drought-stricken areas are discussed.

Host plant resistance (HPR) to whiteflies is rare in cultivated crops. A literature search revealed that HPR research with the Bemisia tabaci/Bemisia argentifolii complex has increased considerably in recent years, but large-scale screening of a wide selection of genotypes is limited. At the International Center for Tropical Agriculture in Colombia, more than 5000 cassava clones have been evaluated for resistance to Aleurotrachelus socialis. Several cultivars with high levels of resistance have been identified. Nymphal mortality was highest on the resistant cassava clone, M Ecu 72 (72.5%) and lowest on the susceptible clones CMC 40 (33%) and M Bra 12 (25.0%). When feeding on resistant genotypes, A. socialis had less oviposition, longer development periods, reduced size and higher mortality than when feeding on susceptible ones. Mortality is highest during the nymphal stages. Several whitefly resistant hybrids have been developed using M Ecu 72 as the resistant female parent. Three hybrids are being evaluated for release by the Colombian Ministry of Agriculture and Rural Development.

Two encyrtid parasitoids, Aenasius vexans Kerrich (Hymenoptera: Encyrtidae) and Acerophagus coccois Smith (Hymenoptera: Encyrtidae), were compared for their degree of dietary specialisation and the impact this has on their foraging strategies. Both parasitoid species are significant for biological control of the cassava mealybug, Phenacoccus herreni, Cox & Williams (Homoptera: Sternorrhyncha) a major Latin American pest of cassava, Manihot esculenta Crantz, an important root crop. Host acceptance and parasitism were analysed in seven mealybug species (with different levels of polyphagy) occurring in and around cassava fields. Results demonstrate that, in this ecosystem, An. vexans is a specialist for P. herreni while Ac. coccois is a generalist on the first and second trophic level. Of the seven mealybug species, P. herreni and P. madeirensis Green were the most acceptable hosts for Ac. coccois, followed by Ferrisia virgata Cockerell. Ac. coccois did not accept the other four mealybug species. The foraging and oviposition behaviour of individual parasitoids was observed in bioassays with cassava leaves infested by P. herreni. The two species used different strategies to locate their host. Aenasius vexans spent significantly more time walking and standing on an infested leaf and examined a host longer than did Ac. coccois. Acerophagus coccois, in contrast, spent more time for oviposition. As a consequence An. vexans parasitised more hosts in a given time than did Ac. coccois. Because the rate of offspring production of the two species did not differ, we conclude that the gregarious Ac. coccois's strategy to deposit several eggs at once might compensate for its relatively low number of ovipostitions, compared with the solitary An. vexans. These findings suggest that, given the advantages and limitations of each species, a multi-species approach to biological control of P. herreni may yield best results.

Three encyrtid parasitoids Apoanagyrus (Epidinocarsis) diversicornis, Aenasius vexans, and Acerophagus coccois (Hymenoptera: Encyrtidae) are used to control the cassava mealybug Phenacoccus herreni Cox & Williams (Sternorrhyncha: Pseudococcidae), an important pest of cassava in South America. The influence of parasitism on the feeding behaviour of mealybugs was studied by observing honeydew secretion and by the electrical penetration graph technique (EPG, DC-system). Honeydew secretions were observed after parasitism until mummy transformation. No strong EPG parameter differences were found between parasitised and control insects. All results indicated that parasitised mealybugs keep feeding on the phloem sap after parasitism until mummy transformation. The main influence of parasitism on EPG parameters is the appearance of a new pattern resembling the E2 pattern at the extracellular level and labelled H. This pattern was also produced with control insects located on an unfavourable feeding site and could be associated with a stress response. It might be related to the still unclear E(c) pattern of aphids. The relationship of H to stylet activities is discussed.

Two encyrtid species, Acerophagus coccois and Aenasius vexans, parasitoids of the cassava mealybug Phenacoccus herreni use a contact kairomone from the body surface of their host as a host-location stimulant. The kairomone was synthesized and identified as O-caffeoylserine based on a combination of chromatographic methods. The synthetic compound was determined to be active.

The solitary endoparasitoid Aenasius vexans Kerrich (Hymenoptera: Encyrtidae) is used for augmentative releases against the cassava mealybug, Phenacoccus herreni Cox & Williams (Sternorrhyncha: Pseudococcidae), an important pest on cassava in South America. In light of the need for large numbers of high quality females, experiments were conducted on host stage suitability and sex allocation. In choice and no-choice experiments, individual female wasps were offered second and third instar, as well as adult, hosts. During the first five days after emergence, the wasps showed a steady increase in the number of hosts they successfully parasitised per day, but the respective secondary sex ratio for each instar remained constant. Parasitism was highest for third instar hosts in no-choice tests, while in choice tests parasitism was highest in both third instars and adults. The later the developmental stage of the host at oviposition, the faster the parasitoids developed and emerged, and for each host stage, the development time of males was shorter than for females. The sex ratio of the wasps emerging from hosts that were parasitised as second instars was strongly male-biased, while the apparently preferred later stages yielded significantly more females than males. Female and male A. vexans emerging from hosts parasitised at the third instar were significantly larger than for the other stages. This may explain the preference for the third instar as well as the female-biased sex ratio, as size is usually positively correlated with higher fitness, especially in females. The results suggest that third instar hosts are the most suitable for rearing high numbers of large females.

The effect of native and recently introduced natural enemies of the cassava mealybug Phenacoccus herreni Cox & Williams in northeastern Brazil is reported in this article. Studies of population fluctuation of the mealybug and its natural enemies were conducted between 1994 and 1997 in three cassava fields located in Muritiba, Itaberaba, and Sao Goncalo, State of Bahia. At least ≈85% of the parasitoids found in those fields were composed of the recently introduced species Apoanagyrus (=Epidinocarsis) diversicornis (Howard), Aenasius vexans (Kerrich), and Acerophagus coccois Smith. A. diversicornis was found in all fields during most of the experimental period, whereas A. coccois and A. vexans were only found in the fields where they had been released. A. diversicornis out-competed A. vexans in Sao Goncalo, but not A. coccois in Itaberaba. Most predators collected belonged to the genera Hyperaspis, Nephus, and Diomus, all of the family Coccinelidae. The results of this work suggest that the concert...

Se recolectaron insectos infectados con hongos en cultivos de yuca en el Valle del Cauca. En laboratorio, se aislaron, purifi­caron e identificaron los hongos Beauveria bassiana (B.b.9601 y B.b.9602) y Aspergillus sp. (Asp.9601). Estos ais­lamientos nativos junto con uno de Metarhizium anisopliae (M.a.9206), proveniente de CENICAFE, se probaron sobre larvas de E. ello. Se determinó la metodología para seleccionar el aisla­miento más patogénico y el mejor méto­do de inoculación entre aspersión a larva, hoja y larva - hoja. Se determinó el instar larval eiás susceptible al aislamiento se­leccionado para establecer la DL50. La individualización de los insectos tratados en cajas de cartón plastificado de 14 x 11.5 x 5 cm con tapa fue la metodolo­gía más adecuada para pruebas de patogenicidad sobre E. ello denominándo­se “Unidad Experimental Múnera-De Los Ríos”. B.b.9601 fue el más patogénico cau­sando mortalidad entre 77.5% y 87.5% presentando diferencias significativas (P

The mealybugPhenacoccus herreniCox & Williams causes considerable damage to cassavaManihot esculentaCrantz. Field surveys conducted between 1988 and 1994 indicated the mealybug was present in 57 municipalities in six States in north-eastern Brazil, in some places reaching high levels of infestation. Several native natural enemy species were found associated with the pest in Brazil. Exotic encyrtid parasitoids were imported and released in fields in the States of Bahia and Pernambuco.Apoanagyrus diversicornis(Howard) was introduced from Colombia, andAcerophagus coccoisSmith, andAenasius vexans(Kerrich) were introduced from Venezuela. By the end of 1996, a total of 35,930 parasitoids had been released. In Bahia,Apoanagyrus diversicorniswas recovered 130, 234, 304 and 550 km from its release site after 6, 14, 21 and 33 months, respectively.Acerophagus coccoiswas recovered at 180 km from its release site nine months after release.Aenasius vexans, however, did not disperse at all despite being consistently recovered at its release site. In Pernambuco, 9010 parasitoids were released from October, 1995 onwards.Acerophagus coccoisandAenasius vexanswere recovered up to 40 km from the release sites after three and five months of their initial releases, respectively. The establishment and dispersal of these parasitoids are discussed.

▪ Abstract Cassava (Manihot esculenta) occupies a uniquely important position as a food security crop for smallholder farmers in areas of the tropics where climate, soils, or societal stresses constrain production. Given its reliability and productivity, cassava is the most important locally produced food in a third of the world's low-income, food-deficit countries. It is the fourth most important source of carbohydrates for human consumption in the tropics, after rice, sugar, and maize. World production of cassava from 1994–1996 averaged 166 million tons/year grown on 16.6 million hectares (ha), for an average yield of 9.9 tons/ha. Approximately 57% is used for human consumption, 32% for animal feed and industrial purposes, and 11% is waste. Africa accounts for 51.3% of the production; Asia, 29.4%; and Latin America, 19.3%. The area planted to cassava in Africa, Asia, and Latin America is 10.3, 3.7, and 2.6 million ha, respectively.

La chinche de la viruela de la yuca Cyrtomenus bergi es una plaga de las raíces de la planta que, por su modo de alimentación, facilita la entrada de patógenos, deteriorando la calidad del producto. En el presente estudio, realiza­do en el Centro Internacional de Agricultura Tropical (CIAT), se inició el desarrollo de un método de cría masivo del nemátodo Heterorhabditis bacteriophora, y a la vez se midió la capacidad de parasitismo que tienen las razas LFR92 y SQC92 de dicho nemátodo sobre C. bergi, con el fin de conocer el estado de desarrollo del insecto más susceptible al ataque del nemátodo; además, determinar si existe diferencia en cuanto al parasitismo en­tre ambas razas y si el insecto presenta una respuesta diferencial a varias dosis de n/ml y la DL50 para cada una de las razas. En cuanto a la capacidad de parasitismo entre las razas LFR92 y SQC92 de H. bacteriophora no se presentó diferencia significativa. El estado de desarrollo de C. bergi más susceptible al ata­que de las dos razas de H. bacteriophora re­sultó ser el 5° estado ninfal; el insecto presentó una respuesta diferencial frente a varias dosis de n/ml. Se halló una DL50 para SQC92 de 826 n/ml, con límites [545;1137], y para LFR92 de 702 n/ml, con límites [81;1551]. La raza LFR92 resultó ser más agresiva que la raza SQC92. H. bacteriophora tiene potencial como agente de control de C. bergi por haber presentado un alto parasitismo y por ser ade­más una raza nativa.

En bioensayos de laboratorio se evaluaron suspensiones de conidias de los hongos Beauveria bassiana (Bals.) Vu ; Metarhizium anisopliae (Metsch.) Sorokin y Paecilomyces lilacinus..(Thom.) Sam son (Deuteromycotina: Hyphomycetes) sobre adultos de Cyrtomenus bergi; (Hemiptera: Cydnidae), combinados con tres sustratos y dos métodos de inoculación; los insectos del tratamiento testigo se inocularon con agua destilada estéril, más Tween 40 al 0.1%. Con respecto a la mortalidad se encontraron dife­rencias significativas de X2=11.9; p 0.01 y de X2-6.39; p 0.05 entre las especies de hongos utilizados y el método de inoculación, respectivamente. La especie M. anisopliae fue la más virulenta y el método de inocula­ción, más efectivo correspondió al de con­tacto tarsal; el papel filtro húmedo se escogió como sustrato para futuros experimentos. Se encontraron diferencias significativas (p 0.05) con respecto a la susceptibilidad entre ninfas y adultos. Las ninfas fueron más sus­ceptibles a M. anisopliae que los adultos. Se escogió el quinto instar para evaluar trece aislamientos de M. anisopliae, de los cuales los más promisorios fueron el 9206, 9236 y el 9501 con mortalidades del 62, 84 y 70%, respectivamente. El aislamiento 9236 mos­tró mayor control de los insectos tratados; con éste se determinó la DL511 de 1.19x 108 conidias viables ml-', con límites de confian­za entre 5.91x103 3.36x109 y tiempo letal entre 4.7 y 8 días. Otra metodología consis­tió en utilizar suelo esterilizado como sustrato tratado con los tres mejores aislamientos en formulación granulada, se detectó que el ais­lamiento 9206 fue superior a lés aislamien­tos 9236 y 9501 con niveles de control de 63.9, 57.2, y 54.5%, respectivamente. Se des­taca el aislamiento 9206 porque fue el más efectivo en el hábitat de la chinche.

El Cyrtomenus bergi, la chinche subterránea de las raíces o chinche de la viruela de la yuca, apareció a comienzos de la década del 80 como una nueva plaga del cultivo de la yuca (Manihot esculenta,) en las principales zonas productoras de Colombia. El daño de este in­secto afecta directamente la calidad del pro­ductó comercial tanto para consumo humano como industrial, aun con bajos niveles de in­festación. El reconocimiento de nematodos nativos asociados con C. bergi se realizó como una alternativa al control químico y cultural. De las ocho localidades se obtuvo un 100% de recuperación de nematodos entomopató­genos. En Manizales, Pereira y Santander de Quilichao se identificaron razas geográficas de la especie Heterorhabditis bacteriophora Poinar, recuperadas tanto del suelo como de chinches muertas en el campo, bajo condicio­nes diversas de clima y características físicas y químicas de suelo. A los nematodos aisla­dos de las localidades restantes se les asignó un código para posteriores referencias mien­tras se establece su identificación.

Se evaluó el potencial del nematodo entomó­geno Steinernema carpocapsae para el con­trol de Cyrtomenus bergi en el laboratorio. Con todos los estados del insecto se evaluaron tres metodologías: a) cajas Petri (100x15m.m) con papel filtro y suelo sin esterilizar, un insecto por unidad y una dosis de 6'788.800 nemato­dos/ml. Los resultados confirman que C. bergi fue parasitado por S. carpocapsae a los 5 y 8 días después de inoculados; b) en el segundo experimento se utilizaron cajas Petri con pa­pel filtro y vasos plásticos (7x7x10cm) con suelo sin esterilizar y 10 insectos de un solo estado por unidad y tres dosis de nematodos 2.000, 4.000 y 6.000 nematodos/ml. No se ob­servó una tendencia clara en el parasitismo des­pués de 2 y 8 días de inoculado; e) en un tercer ensayo se utilizaron vasos plásticos (3,5 x 4 x 4,5cm' con 10 g de arena esterilizada, con un contenido de humedad estándar de 3%, un sólo insecto por unidad y cinco dosis 2.000, 4.000, 6.000, 8.000 y 10.000 nematodos/ml. Los re­sultados mostraron que el adulto fue el estado más susceptible a todas las dosis, con un 58,61% de parasitismo después de 10 días; los menos susceptibles resultaron ser el I y II instares; con 17 y 31%, respectivamente. Un experimento adicional se realizó utilizando la metodología descrita anteriormente con seis dosis de nematodos. El análisis Probit mostró que la dosis para obtener el 50% de parasitis­mo era de 193 nematodos/ml después de 10 días de la inoculación. Los vasos plásticos con arena estéril y con un contenido estándar de humedad fue la unidad experimental más ade­cuada. Los resultados muestran que S. carpo­capsae es un agente potencial para el control biológico de C. bergi.

Neonate larvae of Monduca sexta were tested for susceptibility to five nuclear polyhedrosis viruses and three granulosis viruses using a droplet feeding assay. Autographa californica nuclear polyhedrosis virus (AcMNPV) and Erinnyis ello granulosis virus (EeGV) were found to infect and kill M. sexta larvae, with observed median survival times (ST 50 ) of 94.6 ± 1.7 (SE) and 184.7 ± 24.3 (SE) hr, respectively. M. sexta larvae were also infected with EeGV late in the third instar, bled 8 and 11 days later, and their hemolymph was examined by SDS-PAGE for viral infection-specific proteins. The EeGV-infected larvae showed the presence of an infection-specific protein of molecular weight ca. 33kDa.

Con el propósito de estudiar la viabilidad de un hongo encontrado en el CIAT-Palmira sobre poblaciones de Mononychelus tanajoa, (Bondar), dentro de un manejo integrado de plagas, se fijaron los siguientes objetivos: demostrar la patogenicidad del hongo u hon­gos asociados con los ácaros enfermos me­diante pruebas de inoculación del patógeno a individuos sanos; determinar la biología del patógeno e identificar el o los hongos asocia­dos con los ácaros enfermos. El trabajo se realizó bajo condiciones controladas adecua­das para reproducir los síntomas, cuatro tem­peraturas: 20, 24, 28 y 32°C y dos rangos de H.R.>65% y

El cultivo de la yuca es atacado por varias especies plagas, sobresaliendo en algunas regiones del mundo el piojo harinoso de la yuca, Phenacoccus he­rreni (Cox & Williams). En poblacio­nes de ésta especie, en cultivos de yuca del CIAT, fue observada la presencia de un depredador, el cual fue determi­nado corno Cleothera notata Mulsant. Esto motivó la realización de la eva­luación de su eficiencia, teniendo en cuenta algunos de los factores que se recomiendan para estos fines; por lo tanto se estudió el ciclo biológico a tres temperaturas diferentes (22, 25 y 30°C), la tasa reproductiva, el umbral mínimo de temperatura y el tiempo fisiológico o constante térmica, con el fin de ser comparados con los datos respectivos para la presa. Las anteriores observaciones fueron realizadas en con­diciones de laboratorio en cámaras am­bientales ajustadas a las temperaturas señaladas; los especímenes fueron colonizados y manejados en cajas pe­tri, utilizando como alimento y luga­res de oviposición, ovisacos de la presa. Se encontró que el insecto pasa por cuatro instares larvales y que la dura­ción promedia desde el inicio de la fase larval hasta el estado adulto es de 33,6; 27,2 y 22,1 días a las temperatu­ras 22, 25 y 30°C, respectivamente. La longevidad de la hembra a 22°C fue de 49 días, con un total de 31,6 huevos por hembra y una oviposición diaria de 0,74; a 25°C la longevidad de la hembra fue mayor de 70 días, con un total de 118 huevos por hembra y una oviposición diaria de 1,81. El porcen­taje de eclosión tuvo promedios de 47,8 y 74,97% a 22 y 25°C, respecti­vamente. El umbral mínimo de tempe­ratura fue de 17,82°C y la constante térmica o tiempo fisiológico fue de 373,2 grados -día.

Intensive investigations of genetic variation within and among populations of the whitefly, Bemisia tabaci, are under way in Israel and in Colombia. A polymorphic esterase (EST), which seems to be controlled by a Mendelian locus, has two alleles in sufficiently high frequencies to be useful as a genetic marker. The analysis of more than 10,000 individual adult whiteflies shows genetic differences among localities in the frequencies of the fast (F) and slow (S) alleles. These differences seem to be related to the intensity of insecticide use against the whitefly. The frequency of F is high in unsprayed areas and in control laboratory populations, but is close to zero in heavily-sprayed agricultural areas. The frequency of Fon cotton in agricultural areas is high in winter and spring, but decreases dramatically in the summer (coincidental with the onset of pest-control activities on cotton). A similar temporal pattern on untreated Lantana may be due to migration of adults from agricultural fields. There was no indication of differentiation of populations on different host plants. In Colombia, the difference in EST patterns in different States are very pronounced, suggestive of geographical races. Small samples from Florida, California and Kenya indicate that B. tabaci in different countries may be genetically distinct.