EFFECTS OF Manduca sexta ALLATOSTATIN AND AN ANALOGUE ON THE PEACH-POTATO APHID Myzus persicae (HEMIPTERA: APHIDIDAE) AND DEGRADATION BY ENZYMES IN THE APHID GUT

摘要

The oral toxicity of the C-type allatostatin, Manduca sexta allatostatin (Manse-AS) and the analogue delta R~3 delta R~5 Manse-AS, where R residues were replaced by their D-isomers, were tested against the peach-potato aphid Myzus persicae by incorporation into an artificial diet. Both peptides had significant dose-dependent effects on mortality, growth, and fecundity compared with control insects. The analogue, delta R~3 delta R~5 Manse-AS, had an estimated LC_(50) of 0.31 mu g/mu ldietandwasmorepotentthanManse-AS(estimatedLC50 of 0.58 mu g/mu l diet). At a dose of 0.35 mg delta R~3 delta R~5Manse-AS/mu l diet, 76% of the aphids were dead after 6 days and all were dead after 10 days. In comparison, three times the dose of Manse-AS was required to achieve 74% mortality after 8 days and 98% mortality after 16 days. The degradation ofboth peptides by extracts prepared from the gut of M. persicae was investigated. The estimated half-life of Manse-AS, when incubated with the gut extract from M. persicae, was 31min. Degradation was due to a cathepsin L-like cysteine protease, carboxypeptidase-like activity, endoprotease activity with glutamine specificity, pyroglutamate aminopeptidase activity, andpossibly trypsin-like proteases. The half-life of the delta R~3 delta R~5 Manse-AS analogue was enhanced (73min) with the D-isomers of R appearing to prevent cleavage around the R residues by cathepsin L-like cysteine proteases or from trypsin-like proteases. The greater stability of the analogue may explain its increased potency in M. persicae. This work demonstrates the potential use of Manse-AS and analogues, with greater resistance to enzymatic attack, in aphid control strategies.