Mispatterning in the ommatidia of Apis mellifera pupae treated with a juvenile hormone analogue

Lethal and Sublethal Effects of Pyriproxyfen on Apis and Non-Apis Bees

Pyriproxyfen is a juvenile hormone mimic used extensively worldwide to fight pests in agriculture and horticulture. It also has numerous applications as larvicide in vector control. The molecule disrupts metamorphosis and adult emergence in the target insects. The same types of adverse effects are expected on non-target insects. In this context, the objective of this study was to evaluate the existing information on the toxicity of pyriproxyfen on the honey bee (Apis mellifera) and non-Apis bees (bumble bees, solitary bees, and stingless bees). The goal was also to identify the gaps necessary to fill. Thus, whereas the acute and sublethal toxicity of pyriproxyfen against A. mellifera is well-documented, the information is almost lacking for the non-Apis bees. The direct and indirect routes of exposure of the non-Apis bees to pyriproxyfen also need to be identified and quantified. More generally, the impacts of pyriproxyfen on the reproductive success of the different bee species have to be evaluated as well as the potential adverse effects of its metabolites.

Influence of the insecticide pyriproxyfen on the flight muscle differentiation of Apis mellifera (Hymenoptera, Apidae)

The Brazilian africanized Apis mellifera is currently considered as one of the most important pollinators threatened by the use of insecticides due to its frequent exposition to their toxic action while foraging in the crops it pollinated. Among the insecticides, the most used in the control of insect pragues has as active agent the pyriproxyfen, analogous to the juvenile hormone (JH). Unfortunately the insecticides used in agriculture affect not only the target insects but also beneficial nontarget ones as bees compromising therefore, the growth rate of their colonies at the boundaries of crop fields. Workers that forage for provisions in contaminated areas can introduce contaminated pollen or/and nectar inside the beehives. As analogous to JH the insecticide pyriproxyfen acts in the bee's larval growth and differentiation during pupation or metamorphosis timing. The flighty muscle is not present in the larvae wingless organisms, but differentiates during pupation/metamorphosis. This work aimed to investigate the effect of pyriproxyfen insecticide on differentiation of such musculature in workers of Brazilian africanized honey bees fed with artificial diet containing the pesticide. The results show that the bees fed with contaminated diet, independent of the insecticide concentration used, show a delay in flight muscle differentiation when compared to the control.

Wide mutational spectrum of a gene involved in hormone action and insecticide resistance in Drosophila melanogaster

The Methoprene-tolerant (Met) bHLH-PAS gene in Drosophila melanogaster is involved in the molecular action of juvenile hormone (JH), and mutants result in resistance to the toxic and morphogenetic effects of JH and JH agonist insecticides such as methoprene. A detailed study of Met mutants can shed light on the poorly understood action of JH as well as the molecular basis of Met resistance to JH insecticides. Nine mutant alleles bearing point mutations in Met were examined for penetrance and expressivity of three phenotypic characters: resistance, defective oogenesis, and a novel eye defect. The collection ranged from two weak alleles having less severe phenotypes to strong alleles with severe phenotypes similar to that of a null allele. The point mutations were located in both conserved and nonconserved domains. Both the eye defect, seen as severely malformed ommatidial facets in the posterior margin of the compound eye, and the oogenesis phenotype are nonconditional, whereas expression of the resistance phenotype requires treatment with JH or JH analogs (JHAs) during early metamorphosis. A proposed basis for all the phenotypic characters centers on MET action as a transcriptional regulator of ecdysone secondary-response target genes during metamorphosis. Disruption of MET function either by mutation or by JHA presence during early metamorphosis results in transcriptional misregulation of different target genes, resulting in the pathology seen in either instance. The variety of amino acid changes in MET that resulted in resistance may portend a rapid rise in resistance in response to increased use of JH insecticides in field insect populations.

Microscopy of the Drosophila facet eye: vademecum for standardized fixation, embedding, and sectioning

We describe here a standardized method for histological processing of the Drosophila compound eye. Primary fixation with 2.5% glutaraldehyde, obligatorily supplemented with 0.1% household detergent regularly yielded the best structural preservation, as compared with that of other, more complicated fixation protocols tested. Notably, it proved indispensable not only to cut off the fly's head to facilitate the penetration of the reagents but also to open the chitinous head capsule. For this, we locally pierced the cuticle between the eyes, leaving the head structurally almost intact, a prerequisite for precisely aligning the head for microtomy. We developed a two-step re-embedding procedure allowing for exact and reproducible orientation of the fly heads. Thus, highly comparable series of cross sections through a representative number of ommatidia were obtained. The feasibility of our embedding and sectioning approach is finally demonstrated by three-dimensional reconstructions of the middle segments of the R1, R7, and R8 photoreceptor cells. We present reconstructions from structurally modified ommatidia, as seen after RNAi-mediated depletion of the endosomal adaptor protein p14, and from normal ommatidia corresponding to the wildtype.