BackgroundHoney bees are exposed to phytochemicals through the nectar, pollen and propolis consumed to sustain the colony. They may also encounter mycotoxins produced by Aspergillus fungi infesting pollen in beebread. Moreover, bees are exposed to agricultural pesticides, particularly in-hive acaricides used against the parasite Varroa destructor. They cope with these and other xenobiotics primarily through enzymatic detoxificative processes, but the regulation of detoxificative enzymes in honey bees remains largely unexplored.Methodology/Principal FindingsWe used several approaches to ascertain effects of dietary toxins on bee susceptibility to synthetic and natural xenobiotics, including the acaricide tau-fluvalinate, the agricultural pesticide imidacloprid, and the naturally occurring mycotoxin aflatoxin. We administered potential inducers of cytochrome P450 enzymes, the principal biochemical system for Phase 1 detoxification in insects, to investigate how detoxification is regulated. The drug phenobarbital induces P450s in many insects, yet feeding bees with phenobarbital had no effect on the toxicity of tau-fluvalinate, a pesticide known to be detoxified by bee P450s. Similarly, no P450 induction, as measured by tau-fluvalinate tolerance, occurred in bees fed xanthotoxin, salicylic acid, or indole-3-carbinol, all of which induce P450s in other insects. Only quercetin, a common pollen and honey constituent, reduced tau-fluvalinate toxicity. In microarray comparisons no change in detoxificative gene expression was detected in phenobarbital-treated bees. However, northern blot analyses of guts of bees fed extracts of honey, pollen and propolis showed elevated expression of three CYP6AS P450 genes. Diet did not influence tau-fluvalinate or imidacloprid toxicity in bioassays; however, aflatoxin toxicity was higher in bees consuming sucrose or high-fructose corn syrup than in bees consuming honey.Conclusions/SignificanceThese results suggest that regulation of honey bee P450s is tuned to chemicals occurring naturally in the hive environment and that, in terms of toxicological capacity, a diet of sugar is not equivalent to a diet of honey.

Background: The molecular mechanisms of Plasmodium invasion in mosquito midguts are not well understood. Results: The mosquito midgut peritrophic matrix protein FREP1 binds Plasmodia. Blocking parasite-FREP1 interactions or ablating FREP1 expression reduced P. falciparum infection in mosquitoes. Conclusion: FREP1 functions as a critical host factor that mediates Plasmodium invasion in mosquito midguts. Significance: Targeting FREP1 may inhibit Plasmodium transmission to mosquitoes and the spread of malaria.

Honeybees (Apis mellifera) and their resource-rich nests are hosts to a wide range of saprophytic fungi, including species that produce mycotoxins. The toxicity of aflatoxin B1 (AB1) and ochratoxin A (OTA), products of Aspergillus species often found in honeybee hives, was evaluated and LC 50 values for both toxins were calculated. Workers can tolerate a wide range of concentrations of both OTA and AB1. At low concentrations, AB1 (1 µg/g and 2.5 µg/g diet) and OTA (1 µg/g) did not have any apparent toxic effects on bees. Enhancement of the toxicity of AB1 by piperonyl butoxide (PBO), a known inhibitor of cytochrome P450 monooxygenases, indicates a role for P450s in AB1 detoxification in honeybees. Extracts of propolis, a complex mixture of plant-derived chemicals, including many flavonoids and other phenolic compounds, similarly ameliorated aflatoxin toxicity and delayed the onset of mortality. Collectively, these results suggest that tolerance of AB1 by honeybees may be due to P450-mediated metabolic detoxification. Propolis may serve a hitherto unrecognized role in honey bee health by enhancing the activity of P450 enzymes involved in mycotoxin detoxification. honeybee / aflatoxin B1 / ochratoxin A / cytochrome P450 monooxygenases / piperonyl butoxide / propolis

Gene duplication provides essential material for functional divergence of proteins and hence allows organisms to adapt to changing environments. Following duplication events, redundant paralogs may undergo different evolutionary paths via processes known as nonfunctionalization, neofunctionalization, or subfunctionalization. Studies of adaptive evolution at the molecular level have progressed rapidly by computationally analyzing nucleotide substitution patterns but such studies are limited by the absence of information relating to alterations of function of the encoded enzymes. In this respect, evolution of the Papilio polyxenes cytochrome P450 monooxygenases (P450s) responsible for the adaptation of this insect to furanocoumarin-containing host plants provides an excellent model for elucidating the evolutionary fate of duplicated genes. Evidence from sequence and functional analysis in combination with molecular modeling indicates that the paralogous CYP6B1 and CYP6B3 genes in P. polyxenes have probably evolved via subfunctionalization after the duplication event by which they arose. Both enzymes have been under independent purifying selection as evidenced by the low dN/dS ratio in both the coding region and substrate recognition sites. Both enzymes have maintained their ability to metabolize linear and angular furanocoumarins albeit at different efficiencies. Comparisons of molecular models developed for the CYP6B3 and CYP6B1 proteins highlight differences in their binding modes that account for their different activities toward linear and angular furanocoumarins. That P. polyxenes maintains these 2 furanocoumarin-metabolizing loci with somewhat different activities and expression patterns provides this species with the potential to acquire P450s with novel functions while maintaining those most critical to its exclusive feeding on its current range of host plants.