A survey of indigenous natural enemies attacking Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) was conducted since its first detection in Italy (late 2008), both by collecting T. absoluta-infested materials (cultivated and wild host plants) and by using sentinel tomato plants (pre-infested by T. absoluta in the laboratory) in various sites with diverse ecological features. Plants were exposed in the field for one week, and were observed in order to collect parasitized T. absoluta instars which were kept in the laboratory until adult emergence. Subsequently some parasitoid species were reared in order to study their biological and behavioural traits on T. absoluta. Fourteen hymenoptera species were recovered, among these the most common ones were an ichneumonid, two braconid species and three eulophids (Zappalà et al., submitted). Three species were reproduced in the laboratory on T. absoluta as host. The braconid Bracon nigricans Szepligeti was successfully reared for more than fifty generations with no apparent adverse effects on the parasitoid biological performances. The subsequent works were focused on this species aiming to evaluate under laboratory conditions: potential host stage preference, daily fertility, development life tables, the longevity and fertility at various host densities and diet regimes. The braconid proved to be a gregarious, idiobiont, arrhenotokous ectoparasitoid of T. absoluta mature larvae (4th instar preferred). The survival of the young instars is negatively correlated with the gregariousness rate. Adults fed with a sugar-protein artificial diet lived longer and produced more progeny than those provided only T. absoluta host larvae. The parasitoid progeny was correlated to host densities, and the parasitism rate was higher at lower host densities. Because females should mate multiple times to be able to produce female progeny through their life span, sex-ratio mostly depended of male longevity (i.e. availability of males). Both females and males were reproductively active soon after emergence. Parasitoid females showed intense stinging activity before effectively starting to lay eggs on hosts. During this pre-oviposition activity, parasitoid females inject fluids, presumably venom, for paralyzing hosts and also assessing host suitability for offspring development (based on host size and/or host haemolymphatic kairomone recognition). Furthermore, host feeding behaviour was observed. The proportion of hosts that were permanently parasitized was stable in all the trials. Semi-field and field studies will be conducted in order to evaluate the efficacy of this braconid parasitoid as biological control agent of T. absoluta on tomato in Europe.
|Titolo:||Adaptation of indigenous parasitoids to the invasive tomato pest Tuta absoluta in Italy: biology and behaviour of the braconid wasp Bracon nigricans|
|Data di pubblicazione:||2011|
|Appare nelle tipologie:||4.1 Contributo in Atti di convegno|