Bionomics of phlebotomine sandflies at a peacekeeping duty site in the north of Sinai, Egypt.

A longitudinal entomological survey for sandflies was conducted from 1989 to 1991 at a focus of enzootic cutaneous leishmaniasis in Northeast Sinai, Egypt, within the border region monitored by multinational peacekeepers. Standardized sampling with CDC light traps, oiled paper "sticky traps", and human landing collection was employed to determine monthly trends in species composition, density, sex ratio, and reproductive status of vector sandflies. Each collection method independently defined sandfly seasonality as the period May-November in 1990, and March-October in 1991. Plebotomus papatasi was the only anthropophagic species found and comprised more than 94% of the sandfly population. Two population peaks (May, July) were observed for this species in both survey years. Density of P. papatasi in underground bunkers was higher than outside but inflated by a greater proportion of male flies. During 1990, the proportion of gravid P. papatasi increased progressively during the 5 months period from May to September and averaged 29.5% and 29.7% for interior and exterior collections, respectively. Density of P. papatasi was greater during 1991, but proportions of gravid flies were significantly lower in each survey month and averaged 14.9% and 12.3% for interior and exterior collections, respectively. Seasonal rates of Leishmania-infected P. papatasi averaged 0.8% and 0.9% in 1989 and 1990, but fell to zero in 1991, suggesting an unstable focus of Leishmania major transmission. Proportions of gravid flies may be a valid indicator of the physiological age and epidemiologic importance of the vector sandfly population at this focus. The strong correlation of sticky trap indices to human-landing/biting rates shows that this is an accurate, inexpensive, and no-risk alternative to human bait collections.

Fractionation of organ extracts of Culex pipiens mosquitoes for the isolation of active components that impair biological parameters of the insect.

The previous phase of the present study revealed that when crude extracts of Culex pipiens midgut, ovaries, and salivary glands are injected into New Zealand White (NZW) rabbits (Oryctolagus cuniculus), rabbits immunized with midgut extract exert the greatest negative impact on adult Cx. pipiens survival and fecundity. This study was conducted to further our understanding of the immunogenic nature of the aforementioned antigenic preparations, thus providing data for the ultimate goal of developing a vaccine against the numerous Cx. pipiens-vectored diseases that affect human populations throughout the world. Extracts of Cx. pipiens midgut, ovaries, and salivary glands were fractionated using Sodium Dodecyl Sulphate Polyacrylamide Gel Electrophoresis (SDS-PAGE). The high (> 80.0 to >106.0 kDa) and low (< 18.5 kDa) molecular weight (MW) fractions of midgut extract, high MW fractions (75.0 - <106.0 kDa) of salivary gland extract, and low MW fraction (27.5 kDa) of ovary extract were excised, and used to immunize rabbits. Following immunization, anti-sera from all immunized rabbits were assayed for antibody response using Enzyme-Linked Immunosorbent Assay (ELISA), Enzyme Immunoblot transfer (EIB), and Indirect Fluorescent Antibody Techniques (IFAT). These assays resulted in both high and low MW fractions of midgut extract, with special reference to the midgut extract low MW fraction (18.0 kDa), eliciting the strongest humoral responses in immunized hosts. When Cx. pipiens were fed on rabbits immunized with the low MW fractions of midgut extract, the fecundity and survival rates were significantly less than those of mosquitoes fed on rabbits immunized with the high MW fractions of midgut extract and control rabbits (P < 0.001). It is concluded that, the low MW fraction of midgut extract is highly immunogenic, and the antibody response of immunized rabbits contributes to a significant disturbance in the life cycle of Cx. pipiens and their progeny. This impairment of feeding behavior and reproduction, in turn, could interfere with pathogen transmission.

Identification of Culex pipiens Linnaeus (Diptera: Culicidae) immunogens recognized by host humoral immunity and their impact on survival and fecundity.

Insecticide use continues to be the primary control strategy to reduce insect vector populations. Concerns about insecticide resistance in target organisms, environmental degradation, and possible deleterious impact on human health have led researchers to seek a variety of alternative control strategies. We tested a relatively new method for controlling mosquitoes using host immune response. New Zealand White (NZW) rabbits (Oryctolagus cuniculus) were immunized with salivary gland (SGE), midgut (MGE), or ovary (OVE) extracts from female Culex pipiens L. Immunized rabbits were then exposed to unfed adult mosquitoes which were subsequently observed for changes in survival, fecundity, and hatch success. Parents that fed upon MGE- (P<0.001), SGE- (P<0.018) and OVE- (P<0.018) immunized rabbits experienced significantly higher mortality within 48 hours than parents fed on control rabbits. Midgut extract elicited the strongest effects upon survival (P<0.001), oviposition activity (P<0.001), and hatch success (P<0.001) in the parent generation. Survival (P<0.018), oviposition activity (P<0.001), and hatch success (P<0.001) were likewise strongly reduced in parents fed on SGE-immunized rabbits. Ovary extract-fed parents experienced less pronounced, but significant reductions, in survival (P<0.018) and hatch success (P<0.034). Surviving progeny were most strongly impacted by feeding upon MGE-immunized rabbits. Our study suggests that manipulating host immune response may be a suitable technique for reducing Cx. pipiens mosquito survival and fecundity, and subsequently the potential risk of disease transmission by this species.