Functional characterization of a novel, highly expressed ion-driven sugar antiporter in the thoracic muscles of Helicoverpa armigera.

Sugar transporters (STs), which mainly mediate cellular sugar exchanges, play critical physiological roles in living organisms, and they may be responsible for sugar exchanges among various insect tissues. However, the molecular and physiological functions of insect STs are largely unknown. Here, 16 STs of Helicoverpa armigera were identified. A phylogenetic analysis classified the putative HaSTs into 12 sub-families, and those identified in this study were distributed into 6 sub-families. Real-time polymerase chain reaction indicated that the 16 HaSTs had diverse tissue-specific expression levels. One transporter, HaST10, was highly expressed in thoracic muscles. A functional study using a Xenopus oocyte expression system revealed that HaST10 mediated both H+ -driven trehalose and Na+ -driven glucose antiport activities with high transport efficiency and low affinity levels. A HaST10 knockout clearly impaired the performance of H. armigera. Thus, HaST10 may participate in sugar-supply regulation and have essential physiological roles in H. armigera.

Interaction of fipronil and the red imported fire ant (Solenopsis invicta): Toxicity differences and detoxification responses.

Fipronil (FIP), a phenyl-pryazole pesticide, has been widely used for crop protection due to its broad insecticidal spectrum, especially for urban insect management. FIP also serves as the active ingredient of major baits used for the control of the red imported fire ant (RIFA; Solenopsis invicta). Although a vast majority of laboratory-based research has been performed using worker ants as a model, limited information is available regarding the toxicity of FIP in individuals from different castes and developmental stages. In this study, we investigated the interaction between FIP and this important pest, including FIP toxicity and transformation, RIFA enzyme activity and responses to FIP exposure. The topical and feeding toxicity of FIP in five adult castes, worker larvae and worker pupae were determined and compared. Topical toxicity assays showed that there were significant differences in FIP toxicity among adult workers (LD50 = 1.17 µg/g), larvae (LD50 = 1891.00 µg/g) and pupae (LD50 = 23981.00 µg/g). Although, no obvious differences in topical toxicity were observed among the adult castes, the differences in feeding toxicity were significant. For example, the LC50 value for the workers was 3.96-fold lower than that for soldiers at 24 h, and the LC50 value was slightly lower for male alates than for female alates at day 3 and day 4, respectively. The activities of detoxification enzymes in individuals of different castes and developmental stages were investigated with or without FIP treatment. Cytochrome P450 activity was approximately 24-fold higher in larvae than in workers, and adult workers exhibited 4-fold higher FIP-induced cytochrome P450 activity than individuals from other adult castes. In addition, in vitro experiments demonstrated that FIP was transformed into FIP-sulfone, and this process may be primarily mediated by RIFA P450(s).

Comparative transcriptomic analysis of larval and adult Malpighian tubules from the cotton bollworm Helicoverpa armigera.

Malpighian tubules (MTs) are usually considered the key excretory and osmoregulatory organs of insects. However, increasing evidence has suggested that MTs perform many more functions than just osmoregulation. Until now, the molecular and physiological functions of MTs in the cotton bollworm (Helicoverpa armigera), a very important agricultural pest, are largely unknown. In this study, the transcriptomes of H. armigera MTs from larvae, male adults and female adults were sequenced using RNA-Seq technology, and comparative analyses of transcriptomes between two life stages (larval and adult) and between adult sexes were conducted. We generated a total of 84 643 high-quality unigenes, and identified a large number of abundant transcripts putatively encoding proteins involved in diuresis, detoxification, immunity, carbohydrate transport and metabolism, development and reproduction. We found that the expression pattern of unigenes was relatively similar between female and male adult MTs, but different between larval and adult MTs. Our data suggest that insect MTs may take multiple physiological functions as versatile organs. The extensive alterations in gene expression in MTs occurred from larvae to adults reflect an ecological adaptation to different feeding habits. Sexual dimorphism in the cotton bollworm is somewhat indicated by the transcriptional difference of genes related to carbohydrate metabolism, detoxification, immunity and reproduction in the MTs of male and female adults.