Search

Volatile organic compounds from various plants have received popular interest as one of the vector control tools due to their eco-friendliness and insect-repellent activities. In this study, an excito-repellency assay system was used to examine the noncontact repellency, contact excitation, and knockdown (KD) effects of guava leaf (Psidium guajava L.) oil against Anopheles minimus (Theobald), Anopheles epiroticus (Linton & Harbach), and Culex quinquefasciatus (Say). The organic components of guava oil were identified by gas chromatography–mass spectrometry analysis with dl-limonene (17.4%), cymene (5.49%), and α-terpinene (5.20%) as the major constituents. At concentrations of 2.5 and 5.0%, 100% escape of An. minimus was recorded in the contact assay and 96–98% escape in the noncontact assay. Guava oil stimulated potent irritant (92% escape) and repellent (61–86% escape) effects against Cx. quinquefasciatus. A lower repellency action was observed against An. epiroticus (17–20% escape). No KD effect was observed for guava oil against An. minimus and Cx. quinquefasciatus at any concentration. However, An. epiroticus was more prone to KD effects, with the highest percentage KD (44% in nonescape group) observed with 5.0% guava oil in the noncontact assay. Mortalities of 35% and 11% were observed for An. epiroticus in the nonescape groups in the contact and noncontact assays, respectively. Concentrations of 1.0% and 2.5% guava oil led to

Mosquito control districts in the United States are limited to two main classes of adulticides, pyrethroids and organophosphates, to control mosquitoes. Two adulticides used to control domestic mosquitoes are Fyfanon EW (malathion, organophosphate) and DeltaGard (deltamethrin, pyrethroid). While the effect of these pesticides on European honeybees (Apis mellifera L., Hymenoptera: Apidae) has been investigated, effects on native pollinators need additional research. The purpose of this study was to investigate the acute nontarget effects of these pesticides on Bombus impatiens Cresson (Hymenoptera: Apidae), a native North American bumble bee species, and compare these effects to wild and laboratory strains of mosquitoes (Aedes aegypti (L.) and Culex quinquefasciatus Say, Diptera: Culicidae) through field and laboratory assays. Bombus impatiens was found to be resistant to Fyfanon EW (x̅ = 6.7% mortality at 50-µg malathion per bottle) at levels that caused significant mortality to study mosquitoes (86.2 ≥ x̅ ≥ 100% mortality) in laboratory bottle bioassays. Comparatively, B. impatiens demonstrated greater mortality to DeltaGard (93.3%) at 2.5-µg deltamethrin/bottle than any mosquito colony assayed (14.1 ≥ x̅ ≥ 87.0% mortality). Only DeltaGard was tested in field applications. In the field, we observed acute effects of DeltaGard on mosquitoes and B. impatiens at 25- and 75-m distance from a truck-mounted ultra-low volume fogger, although treatment effects were not significant for B. impatiens. Additional wild-caught nontarget mortality to DeltaGard field trials was also evaluated. This study indicated that common mosquito control adulticides do cause nontarget mortality to B. impatiens but that impacts are variable depending on pesticide and further studies are needed.

Mosquitoes are known to be vectors of numerous diseases leading to human morbidity and mortality at large scale in the world. Insecticide resistance has become a serious concern in controlling the insect vectors of public health importance. Dimethoate is an organophosphate insecticide used to control different insect pests including mosquitoes. Biological parameters of susceptible, unselected, and dimethoate-selected strains of Culex quinquefasciatus Say were studied in the laboratory to recognize resistance development potential and associated fitness cost. The dimethoate-selected strain showed 66.48-fold resistance to dimethoate compared with the susceptible strain after three continuous selections of generations. Realized heritability estimates of dimethoate resistance in Cx. quinquefasciatus yielded a value of 0.19. In dimethoate-selected strain, the biological traits including larval weight, survival from first instar to pupae, fecundity, number of next-generation larvae, relative fitness, net reproductive rate, intrinsic rate of natural increase, and biotic potential were significantly reduced as compared with the unselected strain. However, adult longevity, mean relative growth rate, weight of egg raft, female ratio, pupal duration, and emergence rate of the dimethoate-selected strain did not differ significantly compared with that of the unselected strain. This study provides useful information to devise retrospective management strategy for dimethoate resistance in Cx. quinquefasciatus.

Intensive exposure to insecticides has resulted in the evolution of insecticide resistance in the mosquitoes. We tested the bio-efficacy of two Culex quinquefasciatus Say (Diptera: Culicidae) laboratory strains differentially bio-responsive to pyrethroids to understand the comparative efficacy of different polyfluorobenzyle and conventional pyrethroid molecules and the role of piperonyl butoxide (PBO) in synergizing these molecules in increased tolerance of mosquitoes to these molecules. We have taken deltamethrin (α-cyano pyrethroid with phenoxybenzyl moiety); permethrin (phenoxybenzyl pyrethroid without an α-cyano group); transfluthrin, dimefluthrin, metofluthrin, and meperfluthrin (polyfluorinated benzyl compounds); and prallethrin (modified cyclopentadienone compound) for this study. We found higher bio-efficacy in dimefluthrin, metofluthrin, and meperfluthrin compared with transfluthrin against tested mosquito strains. We found that transfluthrin exhibited synergism with PBO, which supports the hypothesis that P450 enzymes could play a role in the detoxification process of transfluthrin, which was earlier not believed. However, other polyfluorobenzyl pyrethroids with a 4-(methoxymethyl) phenyl capping in the tetrafluorobenzyl ring (dimefluthrin, metofluthrin, and meperfluthrin) exhibit greater synergism with PBO compared with transfluthrin. Further study is required to understand the mechanism for higher synergistic ratios in polyfluorobenzyl pyrethroids with 4-(methoxymethyl) phenyl moiety and ascertain the possible involvement of novel mechanisms that may involve in developing resistance. This is the first report of comparative bio-efficacy of multiple polyfluorobenzyl pyrethroids and PBO synergism against mosquitoes.

The susceptibility of adults and larvae from four field populations of Culex pipiens pallens (Coguillett) (Diptera: Culicidae) in China to deltamethrin, beta-cypermethrin, and permethrin was investigated using the World Health Organization standard susceptibility test methods. One to 2 d old nonblood fed female mosquitoes emerged from pupae resulting from wild-caught larvae (F1 laboratory reared adults) were exposed to various doses of the pyrethroids. The larval bioassay was conducted using a range of concentrations to determine the LC50 values. Using allele-specific polymerase chain reaction, the frequency of the kdr resistance gene was determined in each population. The bioassay data indicated that deltamethrin was the most active larvicide in all four populations with resistance ratios (RR) of 1.6-3.9-fold. This was followed by beta-cypermethrin with RR of 1.1-3.3-fold, while larvae from three mosquito populations from Beijing, Jinan, and Kaifeng had developed resistance to permethrin with RR of 12.6-, 24.0-, and 18.8-fold, respectively. The overall RR of larvae for all insecticides in ascending order was Changchun < Beijing < Kaifeng < Jinan; and ranking of the adult mortality was Changchun < Jinan = Kaifeng < Beijing. For the three pyrethroids tested, the correlation coefficient among the three test methods on the four populations and one lab strain was quite weak. The R value was 0.113-0.320 when we compared kdr detection for kdr% with LC50, -0.565 to -0.793 when kdr% versus adult mortality test, and -0.750 to 0.505 for LC50 versus adult mortality. Permethrin showed the best correlation (R = -0.793) between kdr frequency and adult mortality. This indicates that levels of susceptibility changes to an insecticide should not be based on a single method of assessment.

Coffee husk waste (CHW) discarded as bio-organic waste, from coffee industries, is rich in carbohydrates. The current study emphasizes the management of solid waste from agro-industrial residues for the production of biopesticides (Bacillus sphaericus, and B. thuringiensis subsp. israelensis), to control disease transmitting mosquito vectors. An experimental culture medium was prepared by extracting the filtrates from coffee husk. A conventional culture medium (NYSM) also was prepared. The studies revealed that the quantity of mosquitocidal toxins produced from CHW is at par with NYSM. The bacteria produced in these media, were bioassayed against mosquito vectors (Culex quinquefasciatus, Anopheles stephensi, and Aedes aegypti) and it was found that the toxic effect was statistically comparable. Cost-effective analysis have revealed that, production of biopesticides from CHW is highly economical. Therefore, the utilization of CHW provides dual benefits of effective utilization of environmental waste and efficient production of mosquitocidal toxins.

The sensitivity of the second, third (L3), and fourth (L4) instars of Culex pipiens L. and Ochlerotatus sticticus (Meigen) to two larvicides, temephos and Bacillus thuringiensis variety israelensis (Bti) was tested with and without molting occurring in the experiments. In the first experiment for both tested mosquito species, LC50 values increased from the second to the fourth instar when tested against temephos, whereas for Bti the opposite trend was observed. The highest LC50 value was found for fourth instars of Cx. pipens (0.00405 mg/liter) against temephos and for second instars of Oc. sticticus (0.267 mg/liter) against Bti. The determined LC50 values for the second and third instars of both species decreased with an increased number of molted larvae in the experiments with temephos. For the experiments with Bti molting did not have any significant influence on LC50 values, except a small increase in toxicity during the L3/L4 molt of Oc. sticticus. These findings could help assess and define larviciding, as well as influence the quantity of larvicides needed for an efficient treatment.

Laboratory and field bioassay studies were conducted in southeast Queensland, Australia, on the efficacy of VectoLex Control Granule (CG; active ingredient [AI]:50 Bacillus sphaericus [B.s.] International Toxic Units [ITU]/mg) and VectoLex Water Dispersible Granule (WDG) (AI: 650 B.s. ITU/mg) formulations against third-instar larvae of Culex annulirostris Skuse, Culex quinquefasciatus Say, Culex sitiens Wiedemann, Ochlerotatus rigilax (Skuse), Ochlerotatus. notoscriptus (Skuse), and Aedes aegypti (L.). The Gompertz model for log-linear mortality data were used to determine laboratory 48-h LC95 values. As with foreign evaluations, the B.s. formulations were most effective against Culex spp., with the WDG 10-100 times more effective than the CG on an ITU/mosquito basis. Consequently, Cx. annulirostris and Cx. quinquefasciatus were selected as target species for small-plot field evaluation of WDG efficacy over time. Weekly cohorts of caged third-instar Cx. annulirostris were exposed to replicated low (250 g/ha), medium (500 g/ha), and high (1,000 g/ha) dosages of WDG. Concurrent assessment of Cx. quinquefasciatus mortality outside the cages was also conducted. In water with high organic content, the low rate produced99% Cx. annulirostris mortality at 48 h, decreasing to 79% at week 3 and no control at week 4. The medium and high rates resulted in 100% Cx. annulirostris mortality for 2 wk posttreatment, decreasing to 95% at week 3, and no control at week 4. The WDG was equally effective against Cx. quinquefasciatus. Treatment did not affect water quality or nontarget shrimp and fish species survival.

The production of Bacillus thuringiensis subsp. israelensis (deBarjac) (Bti) as a biopesticide is not cost-effective using existing fermentation technology. In this study, we explored the use of several less expensive alternative culture media (potato, common sugar, and Bengal gram) for the growth and production of Bti. Growth was obtained in all tested media and was comparable to that obtained in conventional medium (Luria-Bertani). Toxicity assays showed that the toxin produced from the novel growth media were effective in killing larvae of Culex quinquefasciatus, Anopheles stephensi, and Aedes aegypti and toxicity was comparable to that produced from Luria-Bertani medium. These observations suggest that potato can be used as a cheap source of culture medium for the production of Bti toxin in mosquito control programs.

The toxicity of an emulsifiable formulation of pirimiphos methyl (Actellic 25EC) on Anopheles gambiae s.s. Giles, Culex quinquefasciatus Say (Diptera: Culicidae), and predator fish Poecilia reticulata Peters (Pisces: Poeciliidae) was investigated. Acute toxicity tests were carried out to determine the effect of the larvicide on mosquito larvae and fish species. To investigate the nontarget effects on P. reticulata, fish of similar size (3.5 +/- 0.2 cm) were randomly selected and exposed for 28 d, under static renewal bioassay, to sublethal concentrations of the larvicide capable of killing 30 and 70% of Cx. quinquefasciatus. The 24 h LC50 value of pirimiphos methyl on the test organisms ranged between 20.44 and 697.30 microg liter(-1). The ultrastructural changes observed in the intestinal cells of P. reticulata were characterized by degenerating cell membranes with gradual loss of gray area in pycnotic nucleus at lower concentration. Marked damage was found at higher concentration including distinct loss of gray areas in cytosol, absence of cristae, numerous ruptures, and several dead cells. Pirimiphos methyl was toxic to a predatory fish species, and for its relevance in vector control and crop protection, warrants cumulative assessment to establish its comprehensive ecological risk, and the dosage required for field larviciding.

The aim of this study was to explore a cost-effective method for the mass production of Bacillus thuringiensis (Bt) by solid-state fermentation. As a locally available agroindustrial byproduct, spent mushroom substrate (SMS) was used as raw material for Bt cultivation, and four combinations of SMS-based media were designed. Fermentation conditions were optimized on the best medium and the optimal conditions were determined as follows: temperature 32 degrees C, initial pH value 6, moisture content 50%, the ratio of sieved material to initial material 1:3, and inoculum volume 0.5 ml. Large scale production of B. thuringiensis subsp. israelensis (Bti) LLP29 was conducted on the optimal medium at optimal conditions. High toxicity (1,487 international toxic units/milligram) and long larvicidal persistence of the product were observed in the study, which illustrated that SMS-based solid-state fermentation medium was efficient and economical for large scale industrial production of Bt-based biopesticides. The cost of production of 1 kg of Bt was approximately US$0.075.

Bacillus thuringiensis (Bt) (Berliner) strain LLP29 produces a crystal protein Cyt1Aa6 toxic to mosquito vectors of human diseases. However, the susceptibility of Culex quinquefasciatus (Say) in the current study was 8.25 times higher than that of Aedes albopictus (Skuse) with this single protein Cyt1Aa6 purified from LLP29. To understand the mechanism of the novel mosquitocidal protein, the binding characteristic of brush border membrane vesicles from the two tested mosquitoes was investigated. Enzyme-linked immunosorbent assay showed that Cyt1Aa6 bound to the two mosquitoes' brush border membrane vesicles. However, the titer of Ae. albopictus was a little higher than that of Cx. quinquefasciatus, with 3.21 and 2.91, respectively. Ligand Western blot analysis showed Cyt1Aa6 toxin specifically bound to the same three proteins (i.e., 68, 54, and 26 kDa) in the two mosquitoes, but one another protein, approximately to 37 kDa, could just be detected in Cx. quinquefasciatus. However, little difference was found in the test of immunohistochemistry. Cyt1Aa6 was detected in the midguts of both mosquitoes with histopathological changes. It would of great importance to the knowledge of the novel toxin against to Cx. quinquefasciatus and Ae. albopictus.

1 tables 3 graph.; International audience; Resistance mechanisms of a strain (PRAIAS) of northern house mosquito, Cu-lex pipiens L., collected in Portugal in 1993, and highly resistant to organophosphates and carbamates, were investigated by comparing the resistance characteristics to 3 organophos-phorous (temephos, chlorpyrifos, malathion) and 1 carbamate (propoxur) insecticides in the presence or absence of synergists; and by determining the possible occurrence of overpro-duced esterases or insensitive acetylcholinesterase (AChE). The reference strain MSE from southern France, with an insensitive AChE, was included in all analyses for comparison. For organophosphorous insecticides, resistance in PRAIAS was caused by an insensitive AChE and an increase in oxidative metabolism. although the 2nd mechanism has only a marginal effect. For propoxur, the insensitive AChE was the only resistance mechanism detected. Biochemical properties of both the French and Portuguese insensitive AChEs were similar. We cannot exclude the possibility that PRAIAS and MSE strains possess exactly the same insensitive AChE allele.

Gynandromorphism in mosquitoes is an infrequent phenomenon which may have useful applications in mosquito physiology, embryology, and genetics, and it could also provide valuable material for the development of non chemical control methods. To study the bilateral sexual expression on the thorax of a damaged, wild-caught northern house mosquito, Culex pippins L., 1758 gynandromorph, statistical discriminant analysis was required. The genotype sex of each wing was assessed by comparing it with a large database of 1,490 C. pipiens individuals for 4 sexually dimorphism wing vein parameters. Both wings were classified as female; therefore, it was concluded that the thorax boundary line was not oblique but rather transverse. The importance of database-linked statistical identification is also discussed.

The southern house mosquito, Culex quinquefasciatus Say, is a competent vector of human disease and an important target of mosquito abatement programs. However, these management programs have been compromised by development of insecticide resistance. In the current study, susceptibilities to naled and resmethrin, two adulticides used in mosquito abatement, were monitored using a topical and contact bioassay, respectively, in five field- collected populations of C. quinquefasciatus (MARC, HOOD1, HOOD2, MINLOVE, and THIB). Frequencies of resistance, measured as survival after treatment with discriminating concentrations (i.e., sufficient to kill90% of a reference susceptible strain) were high (88.0-96.8%) in all field collections treated with naled, but were variable (3.3-94.2%) with resmethrin. In addition, esterase activities in mosquitoes from these collections were quantified using alpha-naphthyl acetate and ranged from 1.08 to 3.39 micromol alpha-naphthol produced min(-1) mg prot(-1). Heightened activities were associated with decreased insecticide susceptibility in HOOD1, THIB, and MINLOVE but not HOOD2. Esterases were visualized using native polyacrylamide gel electrophoresis, and intra- and interstrain differences in banding patterns were detected. In addition, esterases from MINLOVE mosquitoes were more numerous and intensely staining when compared with those from a laboratory-susceptible strain. Finally, naled synergized the toxicity of resmethrin in populations with decreased insecticide susceptibility and increased esterase activity by 2.5-(MINLOVE) to three-fold (THIB). Results from this study will allow management strategies for populations of C. quinquefasciatus to be optimized, and provide a foundation for further studies exploring use of esterase inhibitors as synergists of pyrethroid toxicity.

To investigate insecticide resistance levels and dynamic changes of carboxylesterase polymorphism with time in resistant populations of mosquitoes in the Culex pipiens complex, four field populations were collected in September 2006. The resistance levels of fourth-instar larvae to organophosphate (dichlorvos, parathion, and chlorpyrifos), carbamate (fenobucarb and propoxur), and pyrethroid (permethrin and tetramethrin) insecticides were determined by bioassay. Larvae had a low but significant resistance to organophosphate and carbamate insecticides but no significant resistance to pyrethroid insecticides. Starch gel electrophoresis revealed the presence of the overproduced esterases B1, A2-B2, A8-B8, A9-B9, and All-B11. The frequency of each overproduced esterases varied depending on its regional localities. Compared with previous surveys, the polymorphism of amplified esterase alleles in Beijing populations increased, although the resistance level to organophosphate insecticides declined.

The sensitivity of the second, third (L3), and fourth (L4) instars of Culex pipiens L. and Ochlerotatus sticticus (Meigen) to two larvicides, temephos and Bacillus thuringiensis variety israelensis (Bti) was tested with and without molting occurring in the experiments. In the first experiment for both tested mosquito species, LC50 values increased from the second to the fourth instar when tested against temephos, whereas for Bti the opposite trend was observed. The highest LC50 value was found for fourth instars of Cx. pipens (0.00405 mg/liter) against temephos and for second instars of Oc. sticticus (0.267 mg/liter) against Bti. The determined LC50 values for the second and third instars of both species decreased with an increased number of molted larvae in the experiments with temephos. For the experiments with Bti molting did not have any significant influence on LC50 values, except a small increase in toxicity during the L3/L4 molt of Oc. sticticus. These findings could help assess and define larviciding, as well as influence the quantity of larvicides needed for an efficient treatment.

Esterase activity is monitored in mosquitoes and other arthropod species because high levels of these enzymes can be associated with pesticide resistance. In the 1950s, G. Gomori devised a colorimetric method to detect esterase activity based on their capacity to hydrolyze aryl-esters. We modified this method for use in microtiter plates. Mosquito homogenates (Culex quinquefasciatus Say and C. pipiens L.) from strains susceptible and resistant to insecticides were allowed to hydrolyze alpha-naphthyl acetate in the presence of Triton X-100 and a specific acetylcholinesterase inhibitor. The alpha-naphthol product was detected colorimetrically by a diazo-coupling reaction with Fast Garnet GBC salt. Triton X-100 improved the extraction of esterases and maintained the azo compound in solution. The linear range of the method was 2-20 nmoles of alpha-naphthol; this high sensitivity permitted accurate determinations in 1/30 portions of single adult mosquitoes from the strain with the lowest esterase activity. To avoid variations due to changes in temperature and duration of assay, results were normalized to equivalent enzyme activity units obtained in a spectrophotometer at 25 degrees C. Depending on the number of homogenate dilutions required, performance of the assay in microplates allowed the simultaneous analysis of 20-80 samples. Female mosquitoes showed higher enzyme activity than males when expressed in nmoles/min per mosquito, but differences were reduced when results were expressed as specific activity (nmoles/min per mg protein). A mosquito strain resistant to organophosphates due to the presence of high levels of esterases showed about 200 times more esterase activity than a susceptible strain or a strain resistant due to insensitive acetylcholinesterase.

Laboratory bioassays were conducted on the efÞcacy of a water-dispersible granule (WG) formulation of Bacillus thuringiensis variety israelensis (VectoBac WG; active ingredient (AI): 3,000 Bti international toxic units (ITU)/mg) against third instars of six common Australian mosquito species, Aedes aegypti (L.), Ochlerotatus vigilax (Skuse), Ochlerotatus notoscriptus (Skuse), Culex sitiens Wiedemann, Culex annulirostris Skuse, and Culex quinquefasciatus Say. The normal model for log-linear mortality data was used to determine laboratory 48-h LC50 and LC95 values. The target mosquito species tested were extremely sensitive to the VectoBac WG formulation, with the most sensitive species (Cx. annulirostris and Cx. quinquefasciatus ,L C 95 value of 0.019 ppm) being twice as susceptible as the most tolerant (Oc. notoscriptus ,L C 95 value of 0.037 ppm). Cx. annulirostris was selected as a target species for a small-plot evaluation of VectoBac WG and VectoBac 12 aqueous solution (AS) ((AI): 1,200 Bti ITU/mg) efÞcacy over time, in freshwater in southeastern Queensland, Australia. Replicated cohorts of caged third instars were exposed weekly to six concentrations of WG formulation (0.004 Ð 0.13 ppm) and three concentrations of the 12AS formulation (0.04 Ð 0.13 ppm). In water with high organic content, treatment concentrations of 0.008 ppm WG and 0.04 ppm 12AS and above produced signiÞcant larval control (96%) at 48 h posttreatment, with no residual control at week 1. Water quality was not affected by treatment with either formulation.

The toxicity of boric acid solutions to adult Anopheles quadrimaculatus Say, Culex nigripalpus Theobald, and Aedes albopictus Skuse was evaluated in the laboratory. Median lethal concentrations (LC50 in %) at 24-h exposure for male and female An. quadrimaculatus were 0.317 and 0.885, respectively; for Cx. nigripalpus, 0.273 and 0.560, respectively; and for Ae. albopictus, 0.174 and 0.527, respectively. The LC50 values at 48-h exposure for male and female An. quadrimaculatus were 0.101 and 0.395, respectively; for Cx. nigripalpus, 0.098 and 0.255, respectively; and for Ae. albopictus, 0.078 and 0.244, respectively. In laboratory tests, access for 48 h to sucrose (10%) water containing 1% boric acid (boric acid bait) resulted in 98% mortality in blood fed, gravid, and parous Ae. albopictus. When offered a choice between boric acid bait and sucrose water, 52% of male and 33% of female Ae. albopictus ingested sufficient boric acid bait in 24 h to cause death; after 48 h, respective percent mortalities were 88 and 58%. In outdoor tests, in a walk-in screened cage (156 m3) containing 1,250 female Ae. albopictus, mosquito biting rates on the exposed forearm of a human subject in 3-min exposure were reducedor = 78% for the boric acid bait treatment, compared with a sucrose water control.

Bacterial insecticides play an increasingly important role in mosquito control. To establish guidelines for detecting resistance at an early stage, information on natural variation in susceptibility of insect populations to these insecticides is needed. Between 1990 and 1993, the susceptibility of Culex pipiens L. complex to Bacillus thuringiensis subsp. israelensis de Barjac and/or Bacillus sphaericus Neide was determined in 31 collections from California. These collections were undertaken before the widespread use of B. thuringiensis subsp. israelensis and before the registration of B. sphaericus in California. Seven collections from the Mediterranean island of Cyprus, where no microbial insecticides have been used, also were tested. The 1990-1991 California collections exhibited limited variation in susceptibility to B. thuringiensis subsp. israelensis. LC50 and LC95 values spanned about a three-fold and four-fold range, respectively. The 1993 Cyprus collections exhibited both higher mean LC values, and greater variability in those values, than the California collections. The LC50s for the Cyprus collections varied over a 10-fold range, whereas the LC50s varied over a 12.5-fold range. Variation in susceptibility to B. sphaericus among the 1991 California collections was about five-fold at the LC50 and LC95. No significant geographic variation in susceptibility to B. thuringiensis subsp. israelensis was observed among regions within California. Although variation in susceptibility was limited among California collections, the greater variability observed among the Cyprus collections and between the Cyprus and California collections illustrates the importance of establishing regional baselines to monitor accurately for changes in susceptibility.

Laboratory evaluations were conducted in southeastern Queensland, Australia, to determine the toxicities of two organophosphate compounds (temephos and pirimiphos-methyl), an insect growth regulator (s-methoprene), and an entomopathogenic bacterium (Bacillus thuringiensis variety israelensis de Barjac [B.t.i.]) to Culex annulirostris (Skuse), an Australian freshwater mosquito vector of arboviruses, and to Caradina indistincta Calman, a co-habiting nontarget shrimp species. S-methoprene and B.t.i. were safest for Cx. annulirostris control with lethal dose ratios (LC95 nontarget/LC95 target) of 3,300 and 846,000, respectively. In contrast, lethal dose ratios for temephos and pirimiphos-methyl were 0.05 and 0.00005, respectively, suggesting that they are environmentally unsuitable. Based on their high lethal dose ratios, s-methoprene and B.t.i. are recommended for control of larval Cx. annulirostris in Australian freshwater habitats.

A larval population of Culex quinquefasciatus Say from an urban area (Coque) of Recife, Brazil, submitted to selection with Bacillus sphaericus Neide for a 26-mo trial, was 10 times less susceptible to B. sphaericus and slightly more susceptible to Bacillus thuringiensis israelensis, compared with untreated populations. The low-level resistance to B. splaericus was unstable in the absence of selection pressure. The LC50 of B. sphaericus to the Coque population declined gradually and attained a susceptibility level similar to that observed in a laboratory control colony 16 mo after the treatment period was interrupted. In parallel to the recovery of B. sphacricus susceptibility, Coque larvae also were as susceptible as laboratory larvae to B. thuringiensis israe/ensis.

Amplification of the esterase B1 gene of Culex quinquefasciatus Say results in high titers of an esterase enzyme that confers resistance to organophosphate insecticides. Esterase activity of individuals was measured in samples from an organophosphate resistant strain (Tem-R), a susceptible strain (S-Lb), and their reciprocal F1 progeny. Within-strain variation, as measured by coefficients of variation, was fairly consistent between sexes within strains and among strains (average, 12%). On average, individuals from the Tem-R strain had about 120 times the esterase activity of individuals from the S-Lab strain. The mean esterase activities of the F1 strains were significantly higher than the average of the Tem-R and S-Lab strain mean esterase activities, suggesting enhanced expression of the amplified esterase B1 genes in F1 individuals. Reciprocal F1 strains did not differ significantly in esterase activity or resistance, indicating that maternal effects do not influence either of these measures in these strains. The levels of esterase activity of the strains are discussed in relation to their resistance.

5-31183, 2-[1-methyl-2-(4-phenoxyphenoxy) ethoxyl pyridine, was highly effective in inhibiting normal development of mosquito larvae into adults in laboratory and field trials. Late fourth instars were the most sensitive stage. Mortality occurred in the pupal stage and, at lower doses, resulted in formation of abnormal adults. In highly polluted water, 5-31183 adsorbed onto organic matter and its biological activity persisted for 2 mo after application of 0.11 kg (AI)/ha (0.1 lb/acre). Its persistence in water in the absence of organic matter declined as temperature and sunlight exposure simultaneously increased. Its persistence in relatively “clean” field waters and soil was of short duration. No long-term bioaccumulation problem was apparent following dynamic or static exposures to fish. Nontarget aquatic organisms that coexist in mosquito breeding habitats were not affected adversely by treatments which were effective against mosquitoes. These results indicate efficacy against mosquito larvae, a high degree of safety to associated nontarget organisms, and chemical persistence properties that appear to be compatible with the environment.

The joint toxicity of coprecipitated, free-acid, nondispersible and dispersible formulations of erythrosin B and fluorescein was studied on fourth-instar Culex pipiens quinquefasciatus Say. When used alone or in combination, the dispersible formulation was more toxic than its nondispersible counterparts. The dispersible 1:1 and 1:3 (erythrosin B: fluorescein) combinations were more toxic and faster acting than any of the components used alone. The nondispersible coprecipitated formulation failed to enhance toxicity. However, the dispersible combinations showed synergistic action, with the 1:1 combination exhibiting a greater degree of synergism than the 1:3 combination. The 24-h dark incubation treatment increased the toxic effects of the coprecipitated dispersible formulation and erythrosin B used alone, but suppressed the toxicity of fluorescein.

The esterase patterns of insecticide-resistant and susceptible strains of Culex pipiens fatigans Wiedemann, Culex pipiens pipiens L., C. tarsalis Coquillett, and Anopheles albimanus Wiedemann, were investigated by starch gel electrophoresis. At least one highly active esterase is present in every organophosphate-resistant Strain of Culex spp. A highly active esterase B2, catalyzing the hydrolysis of β-naphthylacetate and being suppressible by DEF® ( S,S,S -tributyl phosphorotrithioate) is most probably associated with organophosphorus multiresistance in C. p. fatigans from California, Esterase B2 has no equivalent in chlorpyrifos-resistant C. p. pipiens from France. Interspecific and interstrain differences in esterase patterns and their relationship to resistance are discussed.

Although Bacillus thuringiensis Berliner var. kurstaki was active against the mosquitoes Aedes aegypti L. and Culex quinquefaciatus Say, it was less active than. B. thuringiensis var. israelensis . The LC50’s (±95% confidence mterval) for B. thuringiensis var. israelensis and B. thuringiensis var. kurstaki against A. aegypti were 0.054 μg/ml (0.042–0.066) and 210.0 μg/ml (139.0–281.4), respectively. Against C. quinquefasciatus , the LC50’s for B. thuringiensis var. israelensis and B. thuringiensis var. kurstaki were 0.11 and >2.2 μg/ml, respectively. Unlike that of previous reports, B. thuringiensis var. israelensis was effecttve against Trichoplusia ni (Hubner), Heliothis zea (Boddie), H. virescens (F.) and comparable to previous commercial products formulated from B. thuringiensis var. thuringiensis and B. thuringiensis var. galleriae , (and it was only one-third to one-tenth less active than current commercial formulations of B. thuringiensis var. kurstaki). The LC50's for B. thuringiensis var. israelensis against T. ni, H. zea , and H. virescens were 109.6, 19.3, and 27.6 μg/ml, respeclively. Corresponding values for B. thuringiensis var kurstaki against T. ni, H. zea, and H. virescens were 15.9, 2.0, and 7.8 μg/ml, respectively.

A broad spectrum of resistance to organophosphorus insecticides has evolved in Culex pipiens quinquefasciatus (= fatigans) Say in California’s San Joaquin Valley. Resistance levels determined on F1 larvae following control failures by chlorpyrifos, involve Abate® ( O, O′ -(thiodi- p -phenylene) O, O, O′O′ -tetramethyl phosphorothioate) at a level of 116.7 times the normal LC50, chlorpyrifos 52.2×, fenthion 48.9×, methyl parathion 24×, malathion 16.4×, and parathion 12.9×. Such multiresistance had appeareel earlier in 2 other major species, Aedes nigromaculis (Ludlow) and Culex tarsalis Coquillett, and is related to the multitude of chemicals employed in mosquito control and agriculture. Resistance in larvae is almost entirely overcome by the synergist DEF ( S, S, S -tributyl phosphorotrithioate) but is unaffected by piperonyl butoxide. Thus, hydrolytic esterases and not mixed function oxidases are implicated as primary resistance mechanisms. Certain synthetic pyrethroids, derivatized carbamates, insect growth regulators, and a biodegradable DDT analogue have demonstrated high activity against the resistant population.

Field and laboratory tests of 2,2,4-trimethyl-1,3-pentanediol (TMPD) as a personal repellent were conducted against the black salt-marsh mosquito, Aedes taeniorhynchus (Wiedemann), in Grand Cayman Island, British West Indies; snowpool Aedes and Culiseta in Alaska; Culex and Anopheles in Jamaica, West Indies; blackflies (Simuliidae) in New York; the chigger Eutrombicula alfreddugesi (Oudemans) and the oriental rat flea, Xenopsylla cheopis (Rothschild), in Florida; and the lone star tick, Amblyomma americanum (L.), in North Carolina. Deet was used as a comparative standard, The results indicated that TMPD at strength equal to deet rates in effectiveness approximately 0.66–1.05 when deet is 1.00.

Many phosphorus esters were evaluated as synergists for malathion against resistant strains of the house fly, Musca domestica L., and the mosquito Culex tarsalis Coquillett. Several were tested as synergists for parathion against parathion-resistant house flies. S, S, S -and O, S, S -trialkyl and mixed alkyl phosphorothioates and phosphorothioates synergized malathion and/or parathion against both insect species. With mosquitoes, butyl-containing esters were most effective; with flies esters containing isopropyl, propyl, or butyl groups were strongly synergistic. S, S -dialkyl O -or S -phenyl phosphorothioites also were active. O, O, O -triphenyl phosphorus compounds synergized malathion against both species; their S, S, S -triphenyl analogs were much less active. In general, tolyl and other substituted phenyl phosphates were malathion synergists against resistant mosquitoes only. The materials synergizing malathion against resistant insects differed considerably from those known to potentiate the toxicity of malathion to mice or to cause ataxia in chickens.

During a 2-year study (1969-70), Psorophora confinnis (Lynch-Arribalzaga), Anopheles quadrimaculatus Say, and A. crucians Wiedemann populations caused statistically significant and economically damaging reductions in the average daily gain of feedlot steers. Steers on a high-energy-level ration (20% roughage) and steers on a low-energy-level ration (60% roughage) that were protected from mosquito attack gained significantly more ( P ‘0.01) during certain periods than steers on the same rations exposed to mosquito attack in 1969 and 1970. During these periods of loss in weight-gain efficiency, 6.8-114.7 blood-fed mosquitoes/ft2 wall were observed in the unscreened barn from 30 to 120 min after official sunset. Steers on the low-energy-level ration which were protected from mosquito attack gained in 1969 18.2 lb/head and sold for $5.78/head and in 1970 gained 45.5 lb/head and sold for $13.12/head more than unprotected steers on the same ration. Mosquito attack did not reduce the economic value of the steers on the high-energy level ration in 1969 and reduced their value only by $0.35/head in 1970 No overall significant difference was found between the average daily feed intake of the steers which were exposed to mosquito attack and those protected by screen wire. Larger numbers of blood-fed mosquitoes were observed in the barn 60, 90, and 120 min after official sunset than at 30 minutes after sunset ( P ‘0.01). However, the rate of increase from 90 to 120 minutes after official sunset was much less than that observed during the 1st 90 minutes.

A new carbamate, RE-11775 ( m-sec -butylphenyl N -methyl- N -(phenylthio) carbamate), has been found which has unusually high toxicity to mosquito larvae. Laboratory and field evaluations demonstrate that it has the potential of being used operationally for control of the larval and adult stages of susceptible and organophosphorus-resistant strains of Aedes nigromaculis (Ludlow). Preliminary studies indicate that RE-11775 also has the potential for controlling susceptible and organophosphorus-resistant strains of Culex spccies. This new carbamate is relatively safe and no adverse properties became apparent during the present tests.

A method is described for evaluating the performance of light traps. The mosquito collections of light traps operated within a few feet of each other showed important differences, especially when the mosquitoes were present in large numbers. These differences were eliminated when the traps constantly changed position. There was no evidence that moving traps caught fewer mosquitoes than stationary traps. Lighted traps caught more mosquitoes than unlighted traps although the latter caught substantial numbers of Culex but not Aedes mosquitoes. The light intensity of the bulb illuminating a trap was directly related to the numbers of individuals of a species taken by that trap, except in the case of C. p. quinquefasciatus females. In fact the number of mosquitoes appeared to be directly proportional to the light intensity, with the exception noted. No repellency was noted at the highest intensities tested. Results with C. p. quinquefasciatus females were not yet clear-cut but females of this species appear to show a low attractance to light on dark nights but not on light ones. The effect of moonlight on females of this species is so pronounced that unlighted traps probably give a much better indication of abundance than lighted ones.

Larvae of 5 susceptible strains and of a highly DDT-resistant strain of the southern house mosquito, Culex pipiens quinquefasciatus Say (= C.p. fatigans Wiedemann), metabolized DDT to DDE (2,2-bis ( p -chlorophenyl)-1,1-dichloroethylene) and 4 strains also produced TDE. Of the susceptible strains, 3 had a high metabolic activity and produced both DDE and TDE and 2 were less active and produced only DDE. Preliminary evidence suggests that the TDE is produced by dechlorination. It was not possible to correlate DDT-resistance with dehydrochlorination, but the resistant strain seemed to be characterized by decreased absorption of DDT and increased excretion of metabolites.

Chemical, physical and biological properties of a new residual insecticide namely Bayer S-1752 (29 493) ( O,O -dirnethyl O-(4-methylthio- m -tolyl)phosphorothioate) are described. Under laboratory conditions residues of S-1752 were tested on glass plates and sun-dried mud against flies ( Musca domestica L.), triatomids ( Rhodnius prolixus Stahl) and mosquitoes ( Culex p. quinquefasciatus Say). Varying exposure and observation times according to the testing animals were used. The results showed that the duration of persistence of S-1752 depends upon the absorptivity of the treated surface. No difference in efficacy of S-1752 was found against susceptible or DDT-resistant house flies.

Most of the homologous series of primary lymphatic amines (long alkyl chains) proved highly effective against eggs of Anopheles albimanus Wireman, but only one of these (solely Maine) proved effective against eggs of the southern house mosquito, Culex pippins quinquefasciatus Say. A beta Maine (beta penta decane amine) also proved effective at 10 ppm concentration against the former species but not against the latter. Species specificity may be attributed to the variations in chorion and micropylar structures and their functioning in the 2 species. Age of eggs as well as duration of treatment period influenced level of susceptibility of eggs to oleyl amine and Neopynamin® (2,2-dimethyl-3-(2-methylpropenyl)cyclopro-panecarboxylic acid ester with N -(hydroxymethyl)-1-cyclo-hexene-1,2-dicarboximide). The younger eggs (1-8 hours old) were more susceptible than older eggs. Longer treatment period (48 hours) produced higher kill of the eggs than a shorter treatment period (24 hours). Exposure periods of shorter than 24 hours produced no marked effects. A kerosene-type petroleum oil (Toxisol J. A. (Jet Aviation grade)) killed eggs of C. p. quinquefasciatus at concentrations of 25 ppm or higher. At these higher concentrations the surface tension of water and/or eggs was lowered to such an extent that the egg rafts sank and mortality in these eggs was high. Mechanical sinking of egg rafts caused similar high mortality of eggs. Embryonic development in eggs treated with effective concentrations was generally retarded. Most of the embryos treated showed no differentiation or were found at the earlier stages of differentiation. However, some embryos in the treated eggs reached full maturity but were not able to emerge.

Grassy plots were treated with granular, wettable powder, and emulsifiable-concentrate formulations of 22 different insecticides to determine their residual life as larvicides. Larvae of Anopheles albimanus Wiedemann, Aedes taeniorhynchus Wiedemann, and Culex pipiens quinquefasciatus Say were used as test insects. Thirteen of the compounds gave satisfactory results for 6 or more weeks against at least one of the test species. Dursban® ( O, O -diethyl O -(3,5,6-trichloro-2-pyridyl) phosphorothioate) at 1 lb/acre was the most effective compound; fenthion at 2 lb/acre and Abate® ( O, O -dimethyl phosphorothioate O, O -diester with 4,4′-thiodiphenol) and Mobam® (benzo[b]thien-4-yl methylcarbamate at 4 lb/acre gave comparable results. At 0.5 lb/acre Dursban gave 6 and >12 weeks of 90% kills of A. taeniorhynchus and A. albimanus . Carbamates, such as propoxur, carbaryl, and Mobam were effective against one or more of the 3 species for >12 weeks when applied at rates of 2 to 4 lb/acre. Residual activity varied markedly with the dosage rate and species tested.