A parasitoid wasp allied with an entomopathogenic virus to control Tuta absoluta

Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is a major threat to worldwide tomato production, and sustainable management methods are needed. Betabaculovirus phoperculellae (PhopGV) and the parasitoid wasp Necremnus tutae Ribes & Bernardo (Hymenoptera: Eulophidae) were identified as promising biocontrol agents of this pest. Since the virus is most effective against first instar larvae, whereas the parasitoid targets older ones, combining both agents could result in increased pest control. We conducted a replicated semi-field experiment to evaluate the control efficacy of N. tutae and PhopGV when used alone and in combination against T. absoluta and their compatibility over an entire growth period. Combining the two agents achieved the highest larval (−24 %) and crop damage (−29 %) reduction cumulated over the entire experiment. However, there was no significant additive effect of the two agents. At the end of the trial, which coincided with the emergence of the third generation of T. absoluta adults, using the virus alone resulted in the strongest reduction of adult density (−78 %), followed by the virus-parasitoid combination (−59 %). No negative effect of the virus was recorded on the parasitoid population. Our results demonstrate the compatibility and potential of N. tutae and PhopGV to reduce population growth and crop damage of T. absoluta under semi-field conditions. While more research is needed, our findings provide important insights into an innovative combination of biocontrol agents, thereby contributing to more sustainable agriculture.

Methods
The data were collected from a semi-field study in Switzerland during the summer growing seasons 2021. Four treatments with seven replicates were set up in a randomized block design in two greenhouses using walk-in (1.50m x 1.75m x 2.50m W x L x H), thrips-proof cages: 1) T. absoluta only as control; 2) T. absoluta and parasitoids (N. tutae); 3) T. absoluta and baculovirus (PhopGV); 4) T. absoluta, parasitoids, and baculovirus. Adult T. absoluta were released in each cage, which contained tomato plants. In the parasitoid and the combined treatment, parasitoids were released. In the virus and the combined treatment, the virus was sprayed on the plant in a water solution. Every week for three generations, T. absoluta larvae and adults were monitored.