Allomones confer resistance to Musa cultivar Pisanglilin against infestation by Odoiporus longicollis [Oliver] and characterization of Allomones

In bioassay guided extraction of pseudostem powder of Pisanglilin by organic solvents we found the larvicidal activity in acetone extract, whose column chromatography by methanol-chloroform mixture separated the extract into 9-fractions, of which the 8th fraction showed larvicidal activity. Subfractionation of the active fraction by column chromatography resulted in the isolation of two larvicidal molecules [Stigmasterol-3-O-glucoside (SOG) and Sulfoquinovosyl diacylglycerol (SQDG)]. Yield of SOG was 0.002 % and SQDG was 0.005 % and both were highly toxic to O. longicollis larvae with LD50 of 0.40 and 0.378 ppm, respectively. Larvae fed these compounds stopped feeding on third day and died within one week. SOG inhibited the amylase and protease activity of gut and induced histolysis in the mid gut. While SQDG inhibited the leucine amino peptidase and trypsin like serine protease activities, which decreased the content of total free amino acids. Imbalance in the activities of aspartate amino transferase and alanine amino transferase disrupted the aminoacid metabolism and the compound inhibited the activity of tyrosinase (an enzyme involved in cuticle development). SQDG toxicity caused accumulation of 20-hydroxyecdysone, the active moulting hormone in the hemolymph. Simultaneous action of two allomones present in Pisanglilin effectively resisted the attack of endophytic larvae in the pseudostem and thereby conferred resistance against infestation by O.longicollis. Preliminary study by intrapseudostem injection of Pisanglilin extract in susceptible M.paradisiaca cultivar Kappa, gave complete protection to it from attack by this pest, under field condition.

Transcriptomic Analysis Reveals Insect Hormone Biosynthesis Pathway Involved in Desynchronized Development Phenomenon in Hybridized Sibling Species of Tea Geometrids (Ectropis grisescens and Ectropis obliqua)

Ectropis grisescens and Ectropis obliqua are sibling species of tea-chewing pests. An investigation of the distribution of tea geometrids was implemented for enhancing controlling efficiency. E. grisescens is distributed across a wider range of tea-producing areas than Ectropis obliqua in China with sympatric distribution found in some areas. In order to explore reproductive isolation mechanisms in co-occurrence areas, hybridization experiments were carried out. Results showed they can mate but produce infertile hybrids. During experiments, the desynchronized development phenomenon was found in the hybridized generation of sibling tea geometrids. Furthermore, transcriptome analysis of those individuals of fast-growing and slow-growing morphs revealed that the insect hormone biosynthesis pathway was enriched in two unsynchronized development groups of hybrid offspring. More importantly, some genes regulating the synthesis of moulting hormone showed significantly up-regulated expression in fast-growing groups. Above all, metabolism of the juvenile hormone and synthesis of the ecdysone pathway were found to be crucially involved in the desynchronized development phenomenon. This research finding contributes to a better understanding of the mechanisms of insect development and reproductive isolation of two sibling species.

Ance, a Drosophila angiotensin-converting enzyme homologue, is expressed in imaginal cells during metamorphosis and is regulated by the steroid, 20-hydroxyecdysone

Ance is a single domain homologue of mammalian angiotensin-converting enzyme (ACE) and is important for normal development and reproduction in Drosophila melanogaster. Mammalian ACE is responsible for the synthesis of angiotensin II and the inactivation of bradykinin and N-acetyl-Ser-Asp-Lys-Pro, but the absence of similar peptide hormones in insects suggests novel functions for Ance. We now provide evidence in support of a role for Ance during Drosophila metamorphosis. The transition of larva to pupa was accompanied by a 3-fold increase in ACE-like activity, which subsequently dropped to larval levels on adult eclosion. This increase was attributed to the induction of Ance expression during the wandering phase of the last larval instar in the imaginal cells (imaginal discs, abdominal histoblasts, gut imaginal cells and imaginal salivary gland). Ance expression was particularly strong in the presumptive adult midgut formed as a result of massive proliferation of the imaginal midgut cells soon after pupariation. No Ance transcripts were detected in the midgut of the fully differentiated adult intestine. Ance protein and mRNA were not detected in imaginal discs from wandering larvae of flies homozygous for the ecd1 allele, a temperature-sensitive ecdysone-less mutant, suggesting that Ance expression is ecdysteroid-dependent. Physiological levels of 20-hydroxyecdysone induced the synthesis of ACE-like activity and Ance protein by a wing disc cell line (Cl.8+), confirming that Ance is an ecdysteroid-responsive gene. We propose that the expression of Ance in imaginal cells is co-ordinated by exposure to ecdysteroid (moulting hormone) during the last larval instar moult to increase levels of ACE-like activity during metamorphosis. The enzyme activity may be required for the processing of a developmental peptide hormone or may function in concert with other peptidases to provide amino acids for the synthesis of adult proteins.