Oral activity of FMRFamide-related peptides on the pea aphid Acyrthosiphon pisum (Hemiptera: Aphididae) and degradation by enzymes from the aphid gut

Insect myosuppressins and myosuppressin analogues were tested for oral toxicity against the pea aphid Acyrthosiphon pisum (Harris) by incorporation into an artificial diet. Acyrthosiphon pisum myosuppressin (Acypi-MS) and leucomyosuppressin (LMS) had significant dose-dependent effects (0.1-0.5 mu g peptide/mu l diet) on feeding suppression, mortality, reduced growth and fecundity compared with control insects, but Acypi-MS was more potent than LMS. One hundred percent of aphids had died after 10 days of feeding on 0.5 mu g Acypi-MS/mu l diet whereas 40% of aphids feeding on 0.5 mu g LMS/mu l diet were still alive after 13 days. Myosuppressins were degraded by aphid gut enzymes: degradation was most likely due to a carboxypeptidase-like protease, an aminopeptidase and a cathepsin L cysteine protease. The estimated half-life of Acypi-MS in a gut extract was 30 min, whereas LMS was degraded more slowly (t(1/2) = 54 mm). No toxicity was observed when the analogues delta R-9 LMS and citrolline(9) Acypi-MS or FMRFamide were fed to the pea aphid. These findings not only help to better understand the biological effects of myosuppressins in aphids but also demonstrate the potential use of myosuppressins in a strategy to control aphid pests. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.