Weak larval competition between the invasive mosquito Aedes japonicus japonicus (Diptera: Culicidae) and three resident container-inhabiting mosquitoes in the laboratory.

The spread of exotic mosquito species into new environments can introduce shifts in mosquito populations and potentially alter public health risks to mosquito-borne diseases. The successful establishment of exotic species may occur due to their competitive advantage over other cohabitating species. We hypothesized that the recently introduced exotic mosquito Aedes japonicus japonicus (Theobald) would be a more effective competitor than Aedes atropalpus (Coquillett) and Aedes triseriatus (Say), and an equal competitor to Culex pipiens (L.) based on larval abundance data within tire habitats. Impacts of competition were measured using the larval developmental rate and survival of larvae, adult mortality, wing length, and sex ratio. We found that intraspecific competition acted strongest against Ae. japonicus versus the other three resident mosquito species by delaying larval development and increasing adult mortality. Interspecific competition was generally weak and significant main effects were only detected for species and density. Overall, our results show that larval competition between Ae. japonicus and the three resident species was weak when present, indicating that other ecological or behavioral factors may be influencing the invasion success for Ae. japonicus in North America.

The effect of three environmental conditions on the fitness of cytochrome P450 monooxygenase-mediated permethrin resistance in Culex pipiens quinquefasciatus.

BACKGROUND: The evolution of insecticide resistance and persistence of resistance phenotypes are influenced by the fitness of resistance alleles in the absence of insecticide pressure. Experimental determination of fitness is difficult, but fitness can be inferred by measuring changes in allele frequencies in appropriate environments. We conducted allele competition experiments by crossing two highly related strains of Culex pipiens quinquefasciatus mosquitoes. One strain (ISOP450) was permethrin resistant (due to P450-mediated detoxification) and one was a susceptible strain. Allele and genotype frequencies were examined for 12 generations under three environmental conditions: standard laboratory, temephos exposure (an insecticide to which the P450 detoxification mechanism in ISOP450 confers no resistance and which is commonly used in mosquito control programs) and cold temperature stress (mimics the colder temperatures within the habitat of this mosquito). RESULTS: A fitness cost was inferred for the P450 mechanism in the standard laboratory environment. A greater cost was associated with the temephos exposed environment, suggesting the temephos placed an additional stress on the P450 resistant mosquitoes. No observed cost was associated with the P450 resistance locus in the cold temperature environment, but there was a significant heterozygote advantage. In all environments the fitness of the resistant homozygotes was the lowest. CONCLUSION: The cytochrome P450-mediated permethrin detoxification resistance in Cx. p. quinquefasciatus can have an associated fitness cost in the absence of permethrin, relative to a susceptible allele. The strength of the cost varies depending on the environmental conditions. P450-mediated resistance is expected to decrease over time if the permethrin application is relaxed and to decrease at an even faster rate if permethrin is replaced with temephos. Additionally, these results indicate that a P450 resistance allele can persist (especially in heterozygotes) in colder temperatures and could potentially be carried into the Culex pipiens hybrid zone.

Development of multifunctional metabolic synergists to suppress the evolution of resistance against pyrethroids in insects that blood feed on humans.

BACKGROUND: Pyrethroids are the insecticides of choice when exposure to humans is likely, such as occurs in vector and public-health-related control programs. Unfortunately, the pyrethroids share a common resistance mechanism with dichlorodiphenyltrichloroethane (DDT), knockdown resistance (kdr), and prior extensive use of DDT has predisposed the pyrethroids to cross-resistance via kdr. Given the widespread occurrence of kdr, the use of synergists with pyrethroids is considered to be prudent to guard against the selection of multiply resistant insects. RESULTS: 3-Phenoxybenzyl hexanoate (PBH) was synthesized as a multifunctional pyrethroid synergist that, besides being a surrogate substrate for sequestration/hydrolytic carboxylesterases, now also functions as a substrate for oxidative xenobiotic metabolism. The addition of PBH to permethrin-treated females of the ISOP450 strain of Culex pipiens quinquefasciatus resulted in a threefold increase in synergism, as judged by the synergistic ratio. Similarly, PBH synergized the action of deltamethrin sixfold on females of the common bed bug, Cimex lectularius, and was 2.8-fold more synergistic than piperonyl butoxide (PBO). CONCLUSIONS: PBH synergized the action of both type I and type II pyrethroids in a mosquito vector (Cx. p. quinquefasciatus) and in a public-health pest, C. lectularius, respectively, indicating a broad spectrum of action on blood-feeding insects. PBH appears to have residual properties similar to permethrin and is itself non-toxic, unlike PBO, and therefore should be compatible with existing pyrethroid formulations used for insecticide-treated nets and home/residential sprays.

Towards a semen proteome of the dengue vector mosquito: protein identification and potential functions.

BACKGROUND: No commercially licensed vaccine or treatment is available for dengue fever, a potentially lethal infection that impacts millions of lives annually. New tools that target mosquito control may reduce vector populations and break the cycle of dengue transmission. Male mosquito seminal fluid proteins (Sfps) are one such target since these proteins, in aggregate, modulate the reproduction and feeding patterns of the dengue vector, Aedes aegypti. As an initial step in identifying new targets for dengue vector control, we sought to identify the suite of proteins that comprise the Ae. aegypti ejaculate and determine which are transferred to females during mating. METHODOLOGY AND PRINCIPAL FINDINGS: Using a stable-isotope labeling method coupled with proteomics to distinguish male- and female-derived proteins, we identified Sfps and sperm proteins transferred from males to females. Sfps were distinguished from sperm proteins by comparing the transferred proteins to sperm-enriched samples derived from testes and seminal vesicles. We identified 93 male-derived Sfps and 52 predicted sperm proteins that are transferred to females during mating. The Sfp protein classes we detected suggest roles in protein activation/inactivation, sperm utilization, and ecdysteroidogenesis. We also discovered that several predicted membrane-bound and intracellular proteins are transferred to females in the seminal fluids, supporting the hypothesis that Ae. aegypti Sfps are released from the accessory gland cells through apocrine secretion, as occurs in mammals. Many of the Ae. aegypti predicted sperm proteins were homologous to Drosophila melanogaster sperm proteins, suggesting conservation of their sperm-related function across Diptera. CONCLUSION AND SIGNIFICANCE: This is the first study to directly identify Sfps transferred from male Ae. aegypti to females. Our data lay the groundwork for future functional analyses to identify individual seminal proteins that may trigger female post-mating changes (e.g., in feeding patterns and egg production). Therefore, identification of these proteins may lead to new approaches for manipulating the reproductive output and vectorial capacity of Ae. aegypti.

Is Apis mellifera more sensitive to insecticides than other insects?

BACKGROUND: Honey bees (Apis mellifera L.) are among the most important pollinators in natural and agricultural settings. They commonly encounter insecticides, and the effects of insecticides on honey bees have been frequently noted. It has been suggested that honey bees may be (as a species) uniquely sensitive to insecticides, although no comparative toxicology study has been undertaken to examine this claim. An extensive literature review was conducted, using data in which adult insects were topically treated with insecticides. The goal of this review was to summarize insecticide toxicity data between A. mellifera and other insects to determine the relative sensitivity of honey bees to insecticides. RESULTS: It was found that, in general, honey bees were no more sensitive than other insect species across the 62 insecticides examined. In addition, honey bees were not more sensitive to any of the six classes of insecticides (carbamates, nicotinoids, organochlorines, organophosphates, pyrethroids and miscellaneous) examined. CONCLUSIONS: While honey bees can be sensitive to individual insecticides, they are not a highly sensitive species to insecticides overall, or even to specific classes of insecticides. However, all pesticides should be used in a way that minimizes honey bee exposure, so as to minimize possible declines in the number of bees and/or honey contamination.