Aphis gossypii (Glover) (Hemiptera: Aphididae) is a highly invasive pest that feeds primarily on phloem resulting in severe economic loss to growers. A. gossypii has cosmopolitan distribution with broad host range, polyphenism, parthenogenetic mode of reproduction, vectoring abilities, and host alteration which has profound influence on its management. Odorant-binding proteins (OBPs) in insects are involved in olfaction, playing a key role in orienting the insect for feeding or oviposition. Recent studies revealed that OBP2 is found in both sensilla trichodea and sensilla basiconica and is preferentially binds to plant volatiles, thus playing crucial roles in host-seeking, detection of oviposition attractants, etc., However, information about the role of OBP2 in A. gossypii (AgOBP2) is still unavailable. In this study, we cloned and characterized OBP2, ortholog from A. gossypii, and the full-length AgOBP2 complementary DNA (cDNA) consisted of 859 bp with an open reading frame of 732 bp. Phylogenetic analysis resulted in grouping of AgOBP2 protein with members of the tribe Aphidini. Further, diet-mediated delivery of double-stranded RNA for AgOBP2 induced silencing, which was evaluated at 48 and 96 h. The reverse transcriptase real-time quantitative polymerase chain reaction (RTq-PCR) results revealed that the level of AgOBP2 messenger RNA (mRNA) was significantly reduced (55-77 %) in dsAgOBP2 treatment after 96 h as compared to the untreated control. The same was reiterated by the electrophysiological responses in the aphids which was reduced (>50 % at 0.25 μg/μl concentration) as compared to the untreated control. Thus, our results showed the potential of gene silencing, possibly to interfere with the odorant perception of A. gossypii for RNAi-mediated pest management. The results from our study provided the first evidence that AgOBP2 play crucial roles in host-seeking, detection of oviposition attractants, etc.; as a result, we suggests that OBP2 could potentially serve as a practicable target for RNAi-mediated gene silencing in hemipteran insect pest control.
Autodetection is an olfactory behavioural process where the females of some species respond to their own pheromonal blends. Through electroantennogram studies it has been proved that the gravid females of Helicoverpa armigera (Hubner) respond to their pheromone blend consisting of Z-11-hexadecenal and Z-9-hexadecenal in the ratio 97 : 3. Male antennae respond more strongly than virgin female antennae. However, antennae of gravid females elicit strong response than unmated males. Also, males showed strong responses in cross-wind flying in wind tunnel experiments, when sex pheromone blends were used. Virgin females and gravid females showed poor response in wind-tunnel studies. The ovipositional experiment where gravid females were allowed to oviposit in the presence and absence of pheromone odours indicated that there was no difference in the number of eggs laid. Through morphological studies, it has been proved that the females also possess sensilla trichoidea, destined to perceive the pheromone blends, though lesser in number than the males. These results support the hypothesis that autodetection of sex pheromones exists in females of H. armigera and is thought to function as a mechanism to induce dispersal under high population densities.
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