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Biological control of Diatraea saccharalis is regarded as one of the best examples of successful classical biological control in Brazil. Since the introduction of the exotic parasitoid, Cotesia flavipes, from Pakistan at the beginning of the 1970s, decrease in D. saccharalis infestation in sugarcane fields has been attributed to the effectiveness of this agent. Recently, the native Tachinidae fly parasitoids (Lydella minense and Paratheresia claripalpis) have also been implicated in this success. However, quantitative data confirming the actual contribution of these agents to the control of D. saccharalis are rather limited. The purpose of this study was to investigate the dynamics of the interactions between D. saccharalis and its parasitoids, emphasizing the temporal patterns of parasitism. To investigate this question, a large data set comprising information collected from two sugarcane mills located in the state of Sao Paulo, Brazil (Barra and Sao Joao sugarcane mills), was analysed. Basically, the data set contained monthly information about the number of D. saccharalis larvae and their parasitoids in each sample (man-hour per sample), the sugarcane varieties cultivated, the age of the sugarcane plants (only at the Sao Joao sugarcane mill) as well as the sugarcane cut at sampling time. The data were collected from March 1984 to March 1997 and from May 1982 to December 1996 for the Barra and Sao Joao sugarcane mills, respectively. Temporal inverse density-dependent parasitism was predominant for both parasitoid species with respect to all spatial scales. Although the temporal pattern of parasitism was not directly density dependent, it was evident that the tachinids and C. flavipes presented positive numerical responses according to variations in D. saccharalis densities through time.

Biological control of Diatraea saccharalis is regarded as one ofthe best examples ofsuccessf ul classical biological control in Brazil. Since the introduction ofthe exotic parasitoid Cotesia flavipes, the decrease of D. saccharalis infestation in sugarcane fields has been attributed to the effectiveness of this agent. Recently, the native tachinid fly parasitoids (Lydella minense and Paratheresia claripalpis) have also been implicated in the success. Here, we investigated the spatial and temporal population interactions between C. flavipes and the tachinid flies, and provide a critical analysis ofthe biological control practice, f on the undesirable effects ofintroductions ofexotic natural enemies. To investigate these questions, a large data set comprising information from two sugarcane mills located in the state ofSao Paulo, Brazil (Barra and Sao Joao Mills), was analysed. Analysis ofthe correlation between C. flavipes and tachinid fly population densities through time revealed that such populations were inversely correlated in the Sao Joao Mill and not correlated in the Barra Mill. Logistic regressions were computed to investigate the proportion ofsites occupied by the parasitoid species at both mills as a f oftime. An increasing trend in the proportion ofsites occupied by C. flavipes was observed, with a concomitant decrease ofthe sites occupied by tachinid flies. This effect was more intense in the Sao Joao Mill. Thus, there is a convincing possibility that constant releases of C. flavipes decreased the tachinid fly populations, resulting in an undesirable effect ofbiological control practice.

Departmento de Ecologia Instituto de Biociencias Universidade Estadual Pailista, Rio Claro, SP

Centro Para Estudos de Insetos Sociais Instituto de Biociencias Universidade Estadual Paulista (UNESP), Rio Claro, Sao Paulo

Horizontal and vertical frequency distribution of larvae in three species of Calliphoridae were studied. Correlation between horizontal and vertical dispersion and larval size was also assessed. The experiment was monitored depositing vials with larvae at one end of a cardboard box covered with wood shavings. Chrysomya megacephala and C. putoria reached 2.9 m from the starting portion of the box. Co. macellaria reached only 2.0 m from the starting portion of the box. The majority of pupae of the three species were found at 4 and 5 cm depth from the surface of the box. Correlation coefficients between pupal size and horizontal and vertical migration were usually very low, and apparently no clear pattern emerges from this data set. This study revealed variation in the dispersion patterns although the two Chrysomya species are more similar in their postfeeding larval behaviour compared to Co. macellaria.

Mapping and collection of ants in cocoa trees in a 1 ha plot in the south of Bahia, Brazil, revealed three dominant species of the ant mosaic : Wasmannia auropunctata, Ectatomma tuberculatum and Azteca chartifex spiriti. A. chartifex demonstrated a larger influence in the cocoa plantation due to its spatial and temporal (1 y) stability in the same cocoa trees, and its capacity for territorial expansion. The management of A. chartifex for controlling insect pests of cocoa is strongly recommended. Considerations of temporal permanence of mosaic dominant ants should be a necessary criteria for ant management in tropical tree crops.

The dispersion patterns of the larval planidia of Ormia depleta was studied in circular arenas. After placing 25 larvae in the center of the arena, their angle of distribution and distance travelled was recorded 15 min later. No innate directional orientations were evidenced, nor was evidence found for either positive or negative orientation to point sound and light sources. In all cases, dispersion was bimodal, with most dispersing only 1 cm, and a much smaller peak found at 10 cm. The bimodality of dispersal distances may be a response to the sexual behavior of its host, mole crickets of the genus Scapteriscus. Zusammenfassung Zur Larvenausbreitung beim Parasitoiden Ormia depleta (Towns.) (Dipt., Tachinidae) Das Ausbreitungsmuster der Larven der Maulwurfsgrillen-Tachine Ormia depleta wurde im Labor auf runden (mit feuchtem Filterpapier bedeckten) Flachen untersucht. Nach Placierung von je 25 Larven im Zentrum der Arena wurden 15 Min. spater der Ausbreitungswmkel und die zuruckgelegte Entfernung registriert. Es wurden weder eine endogene Richtungsorientierung, noch eine positive oder negative Orientierung gegenuber Ton- und Lichtquellen festgestellt. In allen Fallen war die Ausbreitung bimodal mit einem absoluten Ausbreitungsmaximum von nur 1 cm; ein viel geringeres Maximum lag bei 10 cm. Die Bimodalitat der Ausbreitung konnte eine Antwort auf das Sexualverhalten des Wirtes, einer Maulwurfsgrille der Gattung Scapteriscus, sein.

In an institutional setting in Brazil, the pharaoh’s ant, Monornorium phuruonis was found to be the dominant and most abundant ant present throughout the year. The only other regularly collected ant was the exotic Tupinomu melunoce hufum. However, M. phuruonis dominated bait station visitations, although locally concentrated, wit[ other species restricted to regions in which M. phuruonis was not found.

The colonization characteristics of two neighboring populations of Monomorium pharaonis in human structures in Brazil were compared. No differences in the seasonality of colonizations into fixed trap nests between the two populations were found. However, one population had higher frequencies of colonizations with accompanying queens than the other. This resulted in the other population producing new queens at a higher frequency than the other. There was a clumping of colonization attempts at specific points, which shows that colonization may be predictable. These findings may be of importance in control programs for M. pharaonis in structures. Zusammenfassung Zur Dynamik der Ansiedlung und Weibchen-Produktion bei Monomorium pharaonis (L.) (Hym., Formicidae) in Brasilien Es wurden die Ansiedlungsmerkmale von zwei benachbarten Populationen von Monomorium pharaonis im menschlichen Siedlungsbereich in Brasilien vergleichend untersucht. In der Saisonalitat der Ansiedlung wurde zwischen den beiden Populationen kein Unterschied festgestellt. Jedoch hatte eine Population eine hohere Frequenz der Koloniebildung mit den zugehorigen Koniginnen als die andere. Daraus resultierte bei der anderen Population eine Produktion neuer Koniginnen in hoherer Frequenz als in der ersten. Es gab eine Konzentration der Ansiedlungsversuche an spezifischen Stellen, woraus sich eine Vorhersehbarkeit der Ansiedlung ergibt. Diese Ergebnisse konnen fur die Bekampfung der Pharao-Ameise von Bedeutung sein.

The immature development of pharaoh's ant, Monomorium pharaonis, workers was studied in a naturally collected Brazilian population. Three larval instars were confirmed by measuring maximal cephalic widths in cohorts of known age. Minimum egg to adult duration was 25 days, while the maximum duration was 54 days, both of which are larger than those reported for European populations. Larval instar development is cyclical at the colony level, suggesting reproductive bursts followed by lower reproductive activity of the queens. Zusammenfassung Larvenstadien und Entwicklung einer brasilianischen Population der Pharao-Ameise, Monomorium pharaonis (L.) (Hym., Formicidae) Die Entwicklung der Pharao-Ameise, Monomorium pharaonis, wurde anhand einer in Brasilien gesammelten Population untersucht. Mittels Messung der maximalen Kopfkapselbreiten wurden 3 Larvalstadien festgestellt. Die minimale Ei-Adulten-Entwicklungszeit wurde mit 25 Tagen ermittelt, wahrend die Maximaldauer 54 Tage betrug. Beide Werte sind groser als die von europaischen Populationen bekannten. Die Larvalentwicklung verlauft im Kolonie-Bereich zyklisch, woraus hervorgeht, das Phasen starkerer Produktionskraft der Koniginnen mit solchen geringerer Produktion abwechseln.

Ant predation of natural field populations of larval sugarcane borers, Diatraea saccharalis, was evaluated by using insecticidal check techniques, and through survivorship studies of artificial high-density infestations, in plantations in Brazil. Areas of ant suppression had higher levels of D. saccharalis than unsuppressed areas, although both types of areas normally had extremely low D. saccharalis populations. Artifical infestations of D. saccharalis yielded significantly lower larval survivorship in unsuppressed areas than in suppressed areas. Fire ants (Solenopsis spp.) were always the most abundant ant. This study has demonstrated that ants are important pest predators in Brazilian sugarcane fields.

Departamento de Ecologia Instituto de Biociencias Universidade Estadual Paulista, 13506-900 Rio Claro, SP

In many situations, it is difficult to evaluate the location of nests of ants, especially in tropical systems, or to determine which trail system corresponds with which nest, as in the case of high-density populations of leaf-cutting ants, Atta spp. Fragments of colored drinking straws coated with an attractant, generally vegetable oil and/or a starchy carbohydrate, are carried by ants and following removal of the attractant are deposited in middens, allowing determination of the origin of foraging workers. Zusammenfassung Eine einfache Methods zur Lokalisierung von Nestern bei nahrungssuchenden Ameisen am Beispiel von Atta spp. (Hym., Formicidae) Da es manchmal, insbesondere in den Tropen schwierig ist, Ameisennester genau zu lokalisieren oder Ameisenstrasen bestimmten Nestern zuzuordnen, wird hier eine einfache Methode dargestellt. Teile von farbigen Strohhalmen, die mit Frasstimulantien bestreut werden (Pflanzenol und Kohlehydrate) werden von Atta spp. gerne verschleppt. Anhand der verschleppten Nahrungspartikel kann die Herkunft der nahrungssuchenden Ameisen bestimmt werden.

Transplants of incipient colonies of the fire ant, Solenopsis invicta into areas in which mature colonies had been eliminated did not result in higher rates of success than in areas in which mature colonies were present. However, for both types of sites, Pogonomyrmex (Ephebomyrmex) nagelli colonies were found in cleared sites used for transplants, with the number of translocated P. nagelli nests higher in areas which had not been treated with Mirex for S. invicta colony reduction. These results suggest that small colonies may be displaced by larger colonies of other species. Zusammenfassung Versuche zur Verpflanzung junger Kolonien von Solenopsis invicta Bur. (Hym., Formicidae) in Brasilien Verpflanzungen junger Kolonien der Feuerameise, Solenopsis invicta, in Gebiete, in denen reife Kolonien dieser Spezies fehlten, erbrachten keine hoheren Erfolgsraten als bei Ubertragung in bereits mit reifen Solenopsis-Kolonien besiedelte Gebiete. Jedoch wurden in beiden Ubertragungsgebieten reife Pogonomyrmex (Ephebomyrmex) nagelli-Kolonien gefunden, deren Zahl dort hoher war, wo kein Mirex zur Solenopsis-Bekampfung angewandt worden war. Diese Ergebnisse zeigen, das kleine Solenopsis-Kolonien von groseren Kolonien anderer Ameisenarten verdrangt werden konnen.

After exposure of Solenopsis saevissima colonies maintained in plastic trays to phorid attack in the field, and subsequent transfer of colonies to covered plastic buckets, we confirmed that P. wasmanni and P. litoralis are indeed parasitoids of fire ant workers. The period from attack to emergence of phorid adults ranged from 35 to 46 days. Adult phorids were maintained live in glass vials with sugar water as a food source for 5 days. These results indicate that Pseudaceton can be reared for biological control release programs with minimal difficulty. Furthermore, parasitized workers could be easily transferred from South America to quarantine laboratories within the egg to adult emergence time period.

During 1984, collections of 6 species of the genera Scapteriscus and Neocurtilla mole crickets were performed in the state of Sāo Paulo, Brazil. The 6 species differed significantly in terms of numbers of individuals manually excavated or trapped with sound, light or pitfall traps. Moreover, for all species, the frequency of fungal, microbial and nematode infections varied significantly among collection techniques. The evaluation of natural mortality factors is thus shown to rely heavily upon the behavior of each species, and care is needed to assess the relative importance of natural mortality in field populations. Zusammenfassung Fangmethoden fur Maulwurfsgrillen der Gattungen Neocurtilla und Scapteriscus und deren Einflus auf die Einschatzung ihrer naturlichen Pathogene in Brasilien 1984 wurden in Sao Paul, Brasilien, Freilandfange von 6 Arten der Maulwurfsgrillen der beiden Gattungen Neocurtilla und Scapteriscus durchgefuhrt. Die 6 Arten unterschieden sich signifikant hinsichtlich der Anzahl der Individuen, die mit der Hand ausgegraben oder mit Gerausch-, Licht-oder Fangfallen gefangen wurden. Daruber hinaus variierte die Haufigkeit von Pilz-, Mikroorganismen- und Nematoden-Infektionen signifikant in Abhangigkeit von der Fangmethode. Es konnte gezeigt werden, das die Bewertung der naturlichen Mortalitatsfaktoren von der Verhaltensweise der jeweiligen Art abhangt, und das bezuglich der Schatzung der naturlichen Mortalitat im Freiland Vorsicht geboten ist.

Following the nuptial flight, colonization patterns of queens of the leaf-cutting ant, Atta bisphaerica, were studied by means of belt transects. Queen density on the ground following swarming varied from 500 to 13500 queens/ha. Colonization attempts were greater in areas occupied by mature colonies of conspecifics, probably due to disturbance caused by large colonies. However, queen execution by conspecifics was also greater in areas of mature colonies. Approximately 89% of all founding queens were executed, and another 3% were initially lost to predators on the ground in areas with mature colonies. Losses to predators were 59% during the pre-claustral phase in queens in areas of no mature colonies. Zusammenfassung Koloniebildungsmuster der Blattschneider-Ameise, Atta bisphaerica Forel: Ein Nachweis der Populationsregulation Die dem Hochzeitsflug folgenden Koloniebildungsversuche der Atta bisphaerica-Koniginnen wurden mit Hilfe von streifenformigen Transekten untersucht. Die Koniginnendichte auf dem Boden nach dem Schwarmflug variierte zwischen 500 und 13 500 Koniginnen/ha. Versuche, eine Kolonie in Gebieten zu grunden, in denen bereits Kolonien der gleichen Art vorhanden waren, waren haufiger als in bisher unbesiedelten Gebieten. Jedoch wurden Koniginnen in solchen Gebieten auch haufiger durch Artgenossen getotet. In bereits durch Blattschneider-Ameisen besiedelten Gebieten wurden ungefahr 89 % aller gefundenen Koniginnen getotet und weitere 3 % geraubert. In Gebieten, in welchen bisher keine Kolonien vorhanden waren, betrug der Verlust durch Rauber in der Vor-Einschliesungsphase 59 % der Koniginnen.

In Paraguayan and Brazilian pastures with the grass-cutting ants, Atta bisphaerica, A. capiguara, A. laevigata and A. vollenweideri present, cattle were found to limit their grazing activity to areas in which grass-cutting ants were not actively cutting. Cattle confined to areas in which grass-cutting ants were actively cutting grazed significantly less and walked significantly more than cattle confined to areas free of cutting ants. Forage offered to cattle in which workers of grass-cutting ants were placed was consumed significantly less than control treatments, suggesting that the thoracic spines, which are well-developed in Atta spp., may be adaptive in the defense of vegetative resources against large mammalian herbivores, as well as serve other assumed adaptive functions. These results suggest that the impact of grass-cutting ants on Neotropical cattle production is much more complex than estimates of their grazing potential indicate. Zusammenfassung Abhangigkeit der Aktivitat von grasendem Vieh von grasschneidenden Ameisen (Atta spp.) im Suden der neotropischen Region Es wurden auf paraguayaischen und brasilianischen Weiden, die von den Grasschneider-Ameisen Atta bisphaerica, A. capiguara, A. laevigata und A. vollenweideri besiedelt waren, beobachtet, das das Vieh nur an solchen Stellen weitete, wo die Ameisen nicht aktiv waren. Wurden die Weidetiere gezwungen an Stellen zu grasen, wo Atta-Ameisen grasschneidend aktiv waren, frasen sie signifikant weniger und liefen mehr umher als Tiere an ameisenfreien Stellen. Dargereichtes Futter, in dem sich grasschneidende Ameisen belanden, wurden vom Vieh in geringen Mengen als ameisenfreies Futter angenommen. Dies deutet darauf hin, das die Atta-Ameisen ihren gut entwickelten Thorakal-Dorn zur Verteidigung des Grases gegen die herbivoren Sauger einsetzen. Die Ergebnisse zeigen, das die Wirkung grasschneidender Ameisen auf die Viehzuchtung der neotropischen Region uber die Verminderung der Grasmenge hinausgeht.