Variation in organophosphate and carbamate insecticide resistance in relation to esterase activity in Culex (c.) quinquefasciatus Say, 1823 (Diptera: Culicidae)

We determined the existence of the resistance mechanism by means of the esterase enzymes in a Culex (C) quinquefasciatus stock established in the laboratory. Bioassays were performed with insecticides such as malathion and temephos (organophosphoric) and propoxur (carbomate); two cycles were completed during one year. Resistance to malathion was higher. The presence of esterase enzymes in this stock was determined by using synergits and starch gel and paper filter electrophoresis techniques.     

Effect of Wuchereria bancrofti (Cobbold infection on the biological activities of Culex pipiens L. (Diptera: Culicidae) in Egypt

The impact of moderate infection with Wuchereria bancrofti (Cobbold) (25 mf/50 microliters blood) on the biological activities of Culex pipiens L. were investigated. Data revealed that W. bancrofti parasites did not interfere significantly with the oviposition rate (81.97%, 80.228% in non-infected and infected mosquitoes, respectively), fecundity (73.56 +/- 4.56 and 74.23 +/- 5.05 eggs/female) duration of the gonotrophic cycle (6.34 +/- 0.29 and 6.05 +/- 0.26 days), or egg hatchability (88.06% and 90.07%) of infected mosquitoes. Furthermore adult survival to the extrinsic incubation period of infected females (91.8%), did not vary from that of non-infected ones (78.87%). It is suggested that the lack of variations is due to the relatively low level of microfilariae (mf) to which mosquitoes are generally exposed, as revealed by parasite burden. It is concluded that in Egypt the relationship of W. bancrofti to Cx. pipiens is that of a commensal rather than a parasite.     

Resistance to the Cry1Ac delta-endotoxin of Bacillus thuringiensis in the cotton bollworm, Helicoverpa armigera (Lepidoptera: Noctuidae)

Three laboratory strains of Helicoverpa armigera (Hübner) were established by mating of field-collected insects with an existing insecticide-susceptible laboratory strain. These strains were cultured on artificial diet containing the Cry1Ac protoxin of Bacillus thuringiensis using three different protocols. When no response to selection was detected after 7-11 generations of selection, the three strains were combined by controlled mating to preserve genetic diversity. The composite strain (BX) was selected on the basis of growth rate on artificial diet containing Cry1Ac crystals. Resistance to Cry1Ac was first detected after 16 generations of continuous selection. The resistance ratio (RR) peaked approximately 300-fold at generation 21, after which it declined to oscillate between 57- and 111-fold. First-instar H. armigera from generation 25 (RR = 63) were able to complete their larval development on transgenic cotton expressing Cry1Ac and produce fertile adults. There appeared to be a fitness cost associated with resistance on cotton and on artificial diet. The BX strain was not resistant to the commercial Bt spray formulations DiPel and XenTari, which contain multiple insecticidal crystal proteins, but was resistant to the MVP formulation, which only contains Cry1Ac. The strain was also resistant to Cry1Ab but not to Cry2Aa or Cry2Ab. Toxin binding assays showed that the resistant insects lacked the high affinity binding site that was detected in early generations of the strain. Genetic analysis confirmed that resistance in the BX strain of H. armigera is incompletely recessive.     

Bacillus thuringiensis subsp. konkukian (serotype H34) superinfection: case report and experimental evidence of pathogenicity in immunosuppressed mice

We present a case of severe war wounds infected by Bacillus thuringiensis serotype H34 and describe the experimental protocol used to demonstrate its ability to infect mice after cutaneous inoculation. This case is interesting because B. thuringiensis is considered to be a contaminant in laboratories and receives inadequate attention.     

Analysis of 66 kDa toxin from Bacillus thuringiensis subsp. kurstaki reveals differential amino terminal processing of protoxin by endogenous protease(s)

The endogenous protease(s) activated crystal toxin from Bacillus thuringiensis subsp. kurstaki was purified and examined. The purified toxin was homogenous, as demonstrated by two-dimensional polyacrylamide gel electrophoresis and contained 1.38 mumoles neutral sugar and 9 nmoles sialic acid per mg protein amino terminal amino acid sequence data revealed that the toxin is a cleavage product of 132 kDa protoxin with glutamic acid-30 of the deduced amino acid sequence of the crystal protein (Schnepf, H.E., Wong, H.C. and Whiteley, H.R. (1985) J. Biol. Chem. 260: 6264-6272) at the amino terminus.     

Mosquito fauna (Diptera:Culicidae) from Falcon State, Venezuela. I. New records and current checklist

A Markov model was used to assess the cost-benefit ratios of six strategies of screening older drivers for mental status, beginning at age 65. Probabilities of motor vehicle collisions (MVCs), injuries, and fatalities were obtained from national data. Dementia prevalence, test characteristics, and costs were obtained from the literature. Costs included lost wages, car ownership, alternative transportation, and injuries. Using a relative risk of MVC for those with dementia of 5 and a 5% annual discounting rate, the average cost per driver ranged from $51,600 (no testing) to $58,400 (testing every five years). The benefit was < one day of life gained, and the benefits of screening cost approximately 2.8 million dollars per life-year gained. Increasing the relative risk from 5 to 20 substantially improved the cost-benefit of mental status screening. However, mental status screening of older drivers would also be cost-beneficial if physician referral costs were lowered to $60 per evaluation. The authors conclude that a dementia screening program for older drivers would be cost-beneficial if physician evaluations were limited or their cost lowered to < or = $60.     

Susceptibility of three laboratory strains of Aedes albopictus (Diptera: Culicidae) to Japanese encephalitis virus from Taiwan

An 11-year-old boy developed florid reactive periostitis several years after minor trauma. The symptoms responded initially to antibiotics, but after cessation, rapidly recurred and progressed, requiring a ray amputation to relieve the pain and to achieve a functional hand. The reactive periostitis affected the volar aspect of two adjacent phalanges with sparing of the intervening joint, confirming that this is a reactive process rather than a benign neoplasm.     

Development of Wuchereria bancrofti in Culex pipiens L. (Diptera: Culicidae) exposed in the larval instar to sublethal dosages of insecticides and one insect growth regulator and their influence on reproduction of filaria-infected mosquitoes

The effects of exposure of Culex pipiens larvae to sublethel concentrations of larvicides on uptake, development of Wuchereria bancrofti, survival rate and reproduction of filaria-infected mosquitoes were investigated. Fourth instar larvae of Cx. pipiens were exposed to LC40 of the surfactant Triton X-100, the insect growth regulator DPX alone or combined with LC10 of the surfactant and permethrin alone or combined with LC10 of the surfactant. Adults that survived insecticide treatments and controls were infected by allowing them to feed on microfilaremic volunteers. Significant reduction in the uptake of microfilaria was observed in groups treated with Triton X-100 alone or combined either with permethrin or DPX when compared to control. The overall infection and infective rates were significantly reduced in mosquitoes treated with Triton X-100 either alone or combined with permethrin. Treatment with Triton X-100 and DPX prolonged the extrinsic incubation period (EIP) and retarded the development of filarial larvae, while permethrin either alone or combined with Triton X-100 and DPX combined with Triton X-100 shortened the EIP. All larvicides reduced the number of infective larvae (L3)/mosquito and induced deformities among he different parasite stages, especially in mosquitoes treated with combination of permethrin and Triton X-100 or mixture of DPX and Triton X-100 where 36% and 54.9% respectively of L3S were deformed. In treated mosquitoes, a low percentage of L3S was detected in the head and proboscis region while the majority was trapped in the thoracic region. The survival rates of mosquitoes were reduced in cases treated with permethrin, DPX and Triton X-100 while treatment with mixture of DPX and Triton X-100 induced higher rate of mortalities when compared to control. Egg production of filaria- infected Cx. pipiens was significantly reduced in mosquitoes treated with DPX and Triton X-100. It was observed that the addition of Triton X-100 to DPX or to permethrin significantly reduced egg production. The results suggest that sublethal concentrations of larvicides especially Triton X-100 applied to 4th instar larvae of Cx. pipiens could effectively interfere with the development of W. bancrofti in Cx. pipiens and reduced the survival rate and fecundity of the vector.     

Functional maturation of the primate fetal adrenal in vivo: 3. Specific zonal localization and developmental regulation of CYP21A2 (P450c21) and CYP11B1/CYP11B2 (P450c11/aldosterone synthase) lead to integrated concept of zonal and temporal steroid biosynthesis

Previous studies in the primate fetal adrenal gland have indicated that the gland is comprised of three functional zones: 1) the inner fetal zone (FZ), which has the enzymes necessary for dehydroepiandrosterone sulfate (DHEAS) production beginning early in gestation; 2) the transitional zone (TZ), which possesses enzymes necessary for cortisol production; and 3) the outer, definitive zone (DZ), which appears to function as a reservoir of progenitor cells that may populate the remainder of the gland and does not acquire a steroidogenic phenotype with the capacity to produce mineralocorticoids until near term. The enzymes CYP21A2 (P450 21 hydroxylase, or P450c21), CYP11B1 (11beta hydroxylase or P450c11) and CYP11B2 (aldosterone synthase) are necessary for glucocorticoid and mineralocorticoid synthesis but have not been localized previously in an ontogenic manner in the primate fetal adrenal gland. Therefore, we used immunocytochemistry (ICC) to assess specific zonal localization and developmental regulation of CYP21A2 and CYP11B1/CYP11B2 in the human (13-24 weeks' gestation) and rhesus monkey (109 d-term) fetal adrenal gland. In the fetal rhesus, ICC was performed with and without metyrapone administration to the fetus to assess the effects of endogenously increased fetal ACTH. In the human fetal adrenal, CYP21A2 immunoreactivity (IR) was present in only a few isolated cells in the DZ but was detectable in almost all cells in the TZ and FZ. In the fetal rhesus, CYP21A2-IR was present in cells throughout the DZ and TZ and, to a lesser degree, in the FZ. Staining intensity increased with advancing gestational age and was up-regulated in the DZ and TZ, but not the FZ, of the metyrapone-treated fetuses. In the human fetal adrenal gland, CYP11B1/CYP11B2-IR was absent in the DZ but present in the TZ and FZ. In the fetal rhesus monkey adrenal, CYP11B1/CYP11B2-IR was present in all cells of the TZ and FZ but was absent from the DZ until near term. After metyrapone, CYP11B1/CYP11B2-IR was induced in the DZ and was up-regulated in the TZ and FZ. Taken together, these data indicate that in the primate fetal adrenal gland, the FZ has the capacity to synthesize DHEA and DHEAS beginning early in development, the TZ has the capacity to synthesize cortisol after midgestation, and the DZ has the capacity to synthesize mineralocorticoids, but not until near term. The spatial localization of steroid metabolizing enzymes and steroid products in the human and rhesus monkey fetal adrenal suggests analogies of the three functional zones of the fetus (DZ, TZ, and FZ) to their adult counterparts (zona glomerulosa, zona fasciculata, and zona reticularis) and their steroid products (mineralocorticoids, glucocorticoids and androgens, respectively), although the reason for the presence of CYP11B1/CYP11B2- and CYP21A2-IR in the FZ remains to be elucidated.