Mutations of esterase 3 confer two forms of organophosphate resistance on contemporary Australasian Lucilia cuprina. One form, called diazinon resistance, is slightly more effective against commonly used insecticides and is now more prevalent than the other form, called malathion resistance. We report here that the single amino acid replacement associated with diazinon resistance and two replacements associated with malathion resistance also occur in esterase 3 in the sibling species Lucilia sericata, suggesting convergent evolution around a finite set of resistance options. We also find parallels between the species in the geographic distributions of the polymorphisms: In both cases, the diazinon-resistance change is absent or rare outside Australasia where insecticide pressure is lower, whereas the changes associated with malathion resistance are widespread. Furthermore, PCR analysis of pinned specimens of Australasian L. cuprina collected before the release of organophosphate insecticides reveals no cases of the diazinonresistance change but several cases of those associated with malathion resistance. Thus, the early outbreak of resistance in this species can be explained by the preexistence of mutant alleles encoding malathion resistance. The pinned specimen analysis also shows much higher genetic diversity at the locus before organophosphate use, suggesting that the subsequent sweep of diazinon resistance in Australasia has compromised the scope for the locus to respond further to the ongoing challenge of the insecticides.Lucilia cuprina ͉ Lucilia sericata ͉ mutation ͉ convergent evolution ͉ organophosphates O ne of the major unresolved issues in our understanding of adaptive evolutionary change is the extent to which the acquisition of newly beneficial traits proceeds by the selection of existing (preadaptive) rare variants, rather than waiting on new mutations to arise once the selection pressure is imposed. These two scenarios could have very different consequences for the nature of the acquired adaptation, its rate of uptake, and the fate of genetic variation in the chromosomal region surrounding the selected locus. Direct evidence discriminating the two possibilities in natural populations of eukaryotes has been lacking because the critical data needed must include samples that have not been exposed to the selection pressure.The phenomenon of insecticide resistance is proving an informative model for studying microevolutionary processes in eukaryotes because it represents a rapid contemporary acquisition of a major new biochemical phenotype and it generally has a relatively simple genetic basis. The rapidity with which resistance often follows the first use of new pesticides has prompted much speculation about preadaptation at the relevant loci (1, 2). However, many cases have also been recorded where resistant genotypes have fitness costs in the absence of insecticide (3, 4), which would seem at odds with the preadaptation hypothesis. In this paper, we present evidence that tests the hypothesis direct...

The antibacterial properties of secretions aseptically collected from larvae of the greenbottle fly Lucilia sericata (Meigen) (Diptera: Calliphoridae) were examined. These investigations revealed the presence of small (<1 kDa) antibacterial factor(s) within the larval secretions, active against a range of bacteria. These include the Gram-positive Staphylococcus aureus, both methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive Staphylococcus aureus (MSSA), Streptococcus pyogenes and to a lesser extent the Gram-negative Pseudomonas aeruginosa. These secretions were shown to be highly stable as a freeze-dried preparation and, considering the activity against organisms typically associated with clinical infection, may be a source of novel antibiotic-like compounds that may be used for infection control and in the fight against MRSA.

Complementary nuclear (28S rRNA) and mitochondrial (COI + II) gene markers were sequenced from the blowflies, Lucilia cuprina and Lucilia sericata, from Europe, Africa, North America, Australasia and Hawaii. Populations of the two species were phylogenetically distinct at both genes, with one exception. Hawaiian L. cuprina possessed typical L. cuprina-type rRNA, but had L. sericata-type mitochondrial (COI + II) sequences. An explanation for this pattern is that Hawaiian flies are hybrids and comparison of observed levels of sequence divergence to possible introduction events, e.g. Polynesian colonization, suggests that Hawaiian L. cuprina may be evolving rapidly. Moreover, the monophyly of these flies also suggests that the L. sericata mtDNA haplotype was apparently fixed in Hawaiian L. cuprina by lineage sorting, indicating a population bottleneck in the evolutionary history of these island flies.

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