Chemical basis for asymmetric mating isolation between strains of screwworm fly,Cochliomyia hominivorax

Identification of compounds in an HPLC fraction from female extracts that elicit mating responses in male screwworm flies,Cochliomyia hominivorax

When hexane extracts of mature screwworm females were chromatographed on a silica gel column, mating stimulant activity was concentrated in a fraction that eluted with hexane-ether (94∶6, v/v). Separation of this fraction with HPLC (acetonitrile-acetone; 60∶40, isocratic) resulted in a chromatogram of some 20 peaks. Only peaks 4-11 elicited mating responses. Peaks 5-10 had most of the activity, with peak 8 producing the highest response. Sixteen compounds were characterized from peak 8 by gas chromatography-mass spectrometry: six unbranched secondary acetates (C31H62O2); seven previously unreported methyl-branched secondary acetates (C32H64O2); one unbranched ketone (C31H62O); and one methyl-branched ketone (C32H64O). The isomeric acetates were not completely resolved from each other by capillary gas chromatography (CGC) on methyl silicone columns. The sixteenth compound was an aldehyde (C30H60O) that was present only in occasional peak 8 preparations. These compounds and several derivatives were characterized by capillary gas chromatography-mass spectrometry (CGC-MS). The position of the acetate group was ascertained by conversion to a keto group or by replacement of the acetate with a methyl group. Pheromone activity was not observed in peaks trapped either from CGC or by recombination of the trapped CGC peaks from HPLC peak 8. This apparent loss of activity from CGC peaks or from TLC cannot currently be explained.

Enabling technologies to improve area-wide integrated pest management programmes for the control of screwworms

The economic devastation caused in the past by the New World screwworm fly Cochliomyia hominivorax (Coquerel) (Diptera: Calliphoridae) to the livestock industry in the U.S.A., Mexico and the rest of Central America was staggering. The eradication of this major livestock pest from North and Central America using the sterile insect technique (SIT) as part of an area-wide integrated pest management (AW-IPM) programme was a phenomenal technical and managerial accomplishment with enormous economic implications. The area is maintained screwworm-free by the weekly release of 40 million sterile flies in the Darien Gap in Panama, which prevents migration from screwworm-infested areas in Columbia. However, the species is still a major pest in many areas of the Caribbean and South America and there is considerable interest in extending the eradication programme to these countries. Understanding New World screwworm fly populations in the Caribbean and South America, which represent a continuous threat to the screwworm-free areas of Central America and the U.S.A., is a prerequisite to any future eradication campaigns. The Old World screwworm fly Chrysomya bezziana Villeneuve (Diptera: Calliphoridae) has a very wide distribution ranging from Southern Africa to Papua New Guinea and, although its economic importance is assumed to be less than that of its New World counterpart, it is a serious pest in extensive livestock production and a constant threat to pest-free areas such as Australia. In the 1980s repeated introductions and an expansion of Old World screwworm populations were reported in the Middle East; in the 1990s it invaded Iraq and since late 2007 it has been reported in Yemen, where a severe outbreak of myiasis occurred in 2008. Small-scale field trials have shown the potential of integrating the SIT in the control of this pest and various international organizations are considering using the release of sterile insects as part of an AW-IPM approach on a much wider scale. Wohlfahrtia magnifica (Schiner) (Diptera: Sarcophagidae) is a screwworm of temperate regions, which, although of limited agricultural importance, has invaded several new locations in the past few years. This special issue reports on the results of a 6-year project funded by the Joint Food and Agriculture Organization of the United Nations/International Atomic Energy Agency (FAO/IAEA) Programme of Nuclear Techniques in Food and Agriculture entitled 'Enabling Technologies for the Expansion of the SIT for Old and New World Screwworm'. A major goal of the project was to better understand population genetic variation in screwworms as an aid to the identification of isolated populations. The project also addressed issues related to genetic sexing, cuticular hydrocarbons, population dynamics, genetic transformation and chromosome analysis.

Candidate sex pheromones of the New World screwworm Cochliomyia hominivorax

Five novel homologous acetate derivatives of long-chain secondary alcohols and a related ketone were tested for their efficacy as contact mating stimulants for Cochliomyia hominivorax Coquerel (Diptera: Calliphoridae). Full copulatory behaviour at a high percentage was found in tests with racemic 6-acetoxy-19-methylnonacosane at 2.5-20 microg using fertile males from three strains. Males of two strains responded nearly as well to 7-acetoxy-15-methylnonacosane, but an older strain first colonized in 1992 did not respond to this compound. Few or no copulatory responses were obtained to the other secondary alcohol acetates and a related ketone. These two acetate derivatives are the first sex pheromones identified in a calliphorid fly. The threshold of response was also tested, but could not be pinpointed.

Analysis of genetic control of mating behavior in screwworm (Diptera: Calliphoridae) males through diallel crosses and artificial selection

The mode of genetic control of male screw-worm (Diptera: Calliphoridae) mating behavior was examined using diallel cross and artificial selection. Diallel crosses showed strong dominance effects, with hybrids being uniformly more successful in copulation than their more inbred parental strains. Weaker additive and reciprocal effects were also noted. Environmental (replicate) effects were highly significant. Regression of array variances and covariances indicated that epistatic interactions or unequal allele distribution during gametogenesis may have occurred and that high courtship propensity polygenes show dominance over low propensity genes. Artificial selection on males from outbred strains from Guatemala and Belize resulted in a decreased number of mating attempts for lines selected for reduced activity, but mating attempts in lines selected for high mating activity did not increase. A combination of inbreeding during the selection cycles as well as selection for recessive traits would explain this response. The two types of experiments were in general agreement, indicating significant dominance and environmental influence on male mating behavior with weaker additive and possible maternal effects.