Transcriptome Responses to Defined Insecticide Selection Pressures in the German Cockroach (Blattella germanica L.).

Cockroaches are important global urban pests from aesthetic and health perspectives. Insecticides represent the most cost-effective way to control cockroaches and limit their impacts on human health. However, cockroaches readily develop insecticide resistance, which can quickly limit efficacy of even the newest and most effective insecticide products. The goal of this research was to understand whole-body physiological responses in German cockroaches, at the metatranscriptome level, to defined insecticide selection pressures. We used the insecticide indoxacarb as the selecting insecticide, which is an important bait active ingredient for cockroach control. Six generations of selection with indoxacarb bait produced a strain with substantial (>20×) resistance relative to inbred control lines originating from the same parental stock. Metatranscriptome sequencing revealed 1,123 significantly differentially expressed (DE) genes in ≥two of three statistical models (81 upregulated and 1,042 downregulated; FDR P < 0.001; log2FC of ±1). Upregulated DE genes represented many detoxification enzyme families including cytochrome-P450 oxidative enzymes, hydrolases and glutathione-S-transferases. Interestingly, the majority of downregulated DE genes were from microbial and viral origins, indicating that selection for resistance is also associated with elimination of commensal, pathogenic and/or parasitic microbes. These microbial impacts could result from: (i) direct effects of indoxacarb, (ii) indirect effects of antimicrobial preservatives included in the selecting bait matrix, or (iii) selection for general stress response mechanisms that confer both xenobiotic resistance and immunity. These results provide novel physiological insights into insecticide resistance evolution and mechanisms, as well as novel insights into parallel fitness benefits associated with selection for insecticide resistance.

Screening of 57 Candidate Double-Stranded RNAs for Insecticidal Activity Against the Pest Termite Reticulitermes flavipes (Isoptera: Rhinotermitidae).

RNA interference insecticides have received increasing attention in recent years due to their classification as a reduced-risk biopesticide and their proposed faster path to registration compared with conventional synthetic insecticides. The goal of this study was to synthesize and compare efficacy of 62 double-stranded RNAs (dsRNAs) from 31 target genes against the pest termite species, Reticulitermes flavipes (Kollar) (Isoptera: Rhinotermitidae). Fifty-seven dsRNAs of ~125 base pairs each were successfully synthesized. First-tier screens using a combination immersion/feeding assay revealed 10 top candidates and also that dsRNAs coming from synthesis reactions with 80-90× yields were the most effective. Follow-up studies using uptake enhancers in combination with top candidate dsRNAs were unsuccessful. Subsequent concentration range feeding assays on the top candidates revealed two lead termiticidal dsRNAs (3' Hexamerin-2 and 3' Glycosyl Hydrolase Family [GHF] 9-2 cellulase) and another that enhanced feeding (5' GHF9-2 cellulase). Testing a matrix of combinations of these three dsRNAs revealed ultimately that the most consistently effective dsRNA combination was the 3' Hexamerin-2 + 3' GHF9-2 cellulase dsRNA combination. These results provide new information on candidate termiticidal dsRNAs and some apparent factors that have a bearing on their efficacy. Despite these successes, further research and development will be necessary to move dsRNA termiticides from pest management theory to real-world application.

Unique features of a global human ectoparasite identified through sequencing of the bed bug genome.

The bed bug, Cimex lectularius, has re-established itself as a ubiquitous human ectoparasite throughout much of the world during the past two decades. This global resurgence is likely linked to increased international travel and commerce in addition to widespread insecticide resistance. Analyses of the C. lectularius sequenced genome (650 Mb) and 14,220 predicted protein-coding genes provide a comprehensive representation of genes that are linked to traumatic insemination, a reduced chemosensory repertoire of genes related to obligate hematophagy, host-symbiont interactions, and several mechanisms of insecticide resistance. In addition, we document the presence of multiple putative lateral gene transfer events. Genome sequencing and annotation establish a solid foundation for future research on mechanisms of insecticide resistance, human-bed bug and symbiont-bed bug associations, and unique features of bed bug biology that contribute to the unprecedented success of C. lectularius as a human ectoparasite.

Toxicity of Turmeric Extracts to the Termite Reticulitermes flavipes (Blattodea: Rhinotermitidae).

Turmeric is an important spice crop with documented human health benefits associated with chemicals called curcuminoids. In this study, the termite Reticulitermes flavipes (Kollar) was exposed to different solvent extracts of turmeric to investigate potential termiticidal properties. Treating termites with hexane extracts of purified lab-grade curcuminoids had no effect on termites. However, in continuous exposure assays, the LC(50) for hexane extracts of crude turmeric powder was 9.6 mg, or 1.0 mg starting material per square centimeter of filter paper substrate. These active components were soluble in a range of polar and apolar solvents, but only hexane could selectively fractionate active components away from the inactive curcuminoids. The active constituents of turmeric separated by thin layer chromatography (TLC) fluoresced in short-wave UV light but were not visible in long-wave UV light. By re-extracting TLC-separated bands in hexane and performing bioassays and gas chromatography-mass spectrometry, we demonstrated that termiticidal components of turmeric are extractable as a blend containing mainly ar-turmerone, turmerone, and curlone. This determination is consistent with findings of preceding work by other researchers that investigated insecticidal properties of turmeric in other pest insects.