Assessing inoculative releases of Pseudapanteles dignus (Hymenoptera: Braconidae) for the biological control of Tuta absoluta (Lepidoptera: Gelechiidae)

Abstract

Augmentative biocontrol implemented through inoculative seasonal releases of one or more biological control agents has proven to be a reliable crop protection approach in greenhouse and open field crops. The South American tomato pinworm, Tuta absoluta, is a key tomato pest worldwide. In this context, the effectiveness of the American-native larval endoparasitoid Pseudapantales dignus in reducing T. absoluta populations, in a semi-field set-up under greenhouse crop conditions, was assessed. In individual plants enclosed in cages, five host (T. absoluta):parasitoid (P. dignus) relative densities (2:1; 4:1; 4:2; 10:3 and 10:5) were evaluated through inclusion techniques. Controls for each treatment were included. Parasitization was allowed for 48 h; then leaves with signs of moth injury were removed and taken to the laboratory for rearing the host larvae until its pupation or the formation of P. dignus cocoons. Percentages of parasitism were calculated for each treatment and compared using a generalized linear model (GLM) with binomial link function. Pseudapanteles dignus females failed to parasitize at a host density of 2 larvae per plant; meanwhile at the other host densities tested, it reached from 23 to 61% parasitism. The greater percentage of parasitism was observed at host:parasitoid relative densities of 10:3. This field experiment showed evidence that the efficiency of this biocontrol agent decreases at low host densities, probably influenced by a reduction in host localization stimuli. Besides, at higher P. dignus release rates, parasitism decreased due to self-limitation of adult females by mutual interference when searching for hosts. Pseudapantales dignus has a significant potential for use in biological control programs.