The western corn rootworm (WCR) Diabrotica virgifera virgifera LeConte is a major pest of corn that has evolved resistance to transgenic maize that produces insecticidal Cry toxins. The specific mode of action of Cry3Bb1 and mechanism of resistance in WCR are unknown. This study compared gene expression between Cry3Bb1-susceptible and Cry3Bb1-resistant WCR neonates, in the presence and absence of Cry3Bb1. RNA-Seq data were analyzed to identify differentially expressed transcripts between strains of WCR, providing candidate transcripts for resistance to Cry3Bb1. Constitutive and Cry3Bb1-induced differences between strains caused the differential expression of 608 transcripts after 8 hr. Differentially expressed transcripts between strains included ABC transporters, proteases and α-amylases, which known to be receptors or activators of Cry toxins and involved in resistance to Cry toxins in other insects. The response to Cry3Bb1 treatment resulted in approximately 5,000 differentially expressed transcripts in the susceptible strain and included the same annotation categories found between strains but also included metalloproteases, cadherins and signaling proteins. None of these annotations were identified digitalcommons.unl.edu R a u l t e t a l . i n J o u r n a l o f A p p l i e d E n t o m o l o g y ,2 0 1 8 2in the response of the resistant strain to Cry3Bb1, which was represented by only 12 transcripts. Tissue-specific expression analysis of selected transcripts revealed that an α-amylase and a protease were expressed in the midgut, the target organ of Cry toxins. A protease inhibitor and two ABC transporters were expressed outside the midgut, suggesting a limited role in resistance. Numerous polymorphic sites were identified from the RNA-Seq data that showed allele frequency differences between the resistant and susceptible strains. Analysis of these polymorphisms in a larger set WCR strains suggested that the differences were due to genetic drift rather than being associated with resistance to Cry3Bb1. Polymorphisms identified in genes with known roles in resistance to Cry toxins did not appear to differ in frequency between resistant and susceptible strains.

Aedes aegypti is a vector of viruses that negatively impact human health. Insecticide resistance complicates mosquito control efforts, but understanding the mechanisms of resistance can help to improve management practices. This study examined different factors that could influence the interpretation of toxicity bioassays and gene expression studies in A. aegypti, including sex and age, in the context of resistance to pyrethroids. Bioassays using a pyrethroid-resistant strain, Puerto Rico (PR), and a pyrethroid-susceptible strain, Rockefeller (Rock), of A. aegypti were conducted with females and males of three age groups to determine differences in mortality induced by deltamethrin. Overall, strain was the only factor with a significant effect on the LD50. Enzyme assays showed that cytochrome P450 monooxygenase activity in PR was constitutively higher than in Rock, and that pretreatment with the cytochrome P450 inhibitor piperonyl butoxide (PBO) followed by a topical application of deltamethrin (LD25) significantly increased mortality in both strains. Evaluation of the expression levels of seven CYP9J genes previously reported to be 1 digitalcommons.unl.edu

The use of synthetic insecticides to limit the spread of mosquito-borne disease faces a number of significant challenges, including insecticide resistance, concerns related to the environmental impact of widespread insecticide use, as well as slowed development of new insecticide chemistries. One important alternative to broadcast insecticides is the use of personal protection strategies to limit contact with vector species, including the use of spatial repellents that can employ synthetic pyrethroids or botanical products to effect control. A currently underexplored area of research involves the investigation of botanical products for their potential to serve as insecticide synergists when delivered as a vapor. This study describes the development of an assay that facilitates the screening of essential oils delivered as a vapor for enhancement of deltamethrin efficacy in both pyrethroid-susceptible and-resistant strains of the vector mosquito species Aedes aegypti. Deltamethrin efficacy was significantly increased following exposure to cinnamon (Cinnamomum cassia),

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