Protective effect of Wolbachia in Anastrepha fraterculus (Diptera: Tephritidae) against the attack of the parasitoid Diachasmimorpha longicaudata (Hymenoptera: Braconidae).

CONTE, CLAUDIA A; NUSSENBAUM, ANA L; MILLA, FABIÁN; BOURTZIS, KOSTAS; CLADERA, JORGE L; SEGURA DIEGO F.; LANZAVECCHIA, SILVIA B.

Tapachula

Simposio; 10th International Symposium on Fruit lies of Economic Importance.; 2018

Background: The South American fruit fly Anastrepha fraterculus is widespread in the American continent and it is a quarantine pest in Argentina. Nowadays, only chemical control is applied against this pest. Diachasmimorpha longicaudata is a parasitoid of larval stages of tephritid flies that could potentially be applied as an environmentally friendly strategy to control A. fraterculus. In this regard, studies focusing on the identification of endosymbionts in this fly-parasitoid system are of relevance. The reproductive bacterium Wolbachia has been previously detected in A, fraterculus and it was found absent in D. longicaudata. In addition, two different strains of Wolbachia were recently described in a laboratory colony from Argentina. In the present work, we indirectly evaluated the role of Wolbachia on the immune response of A. fraterculus larvae against D. longicaudata eggs by means of a parasitism assay.Methods: A. fraterculus larvae infected with two different strains of Wolbachia (AfraCast2, AfraCast1) and A. fraterculus Wolbachia-cured lines (Rif-AfraCast2, Rif-AfraCast1), were exposed to virgin and sexually mature D. longicaudata females by the method of forced parasitism developed in the laboratory. Exposed larvae were conditioned in larval diet to continue their development. After all insects (flies and parasitoids) had emerged, they were counted and the percentages of parasitism were calculated. Not-emerging pupae were dissected for species determination. Wolbachia presence was evaluated by 16S rRNA PCR. The results were compared using a paired T-test. Results: The percentage of parasitism was significantly different between Rif-AfraCast2 and AfraCast2 (t = 2.901, p = 0.027, d.f. = 6). Wolbachia cured strains showed higher percentage of parasitism than infected strains (infected = 82.4 ± 6.5%, cured = 94.0 ± 5.1%). The percentage of parasitism between Rif-AfraCast1 and AfraCast1 showed a similar trend (infected = 87.0 ± 10.7%, cured = 91.5 ± 1.0%) but differences did not reach the level of significance (t = 0.841, p = 0.432, d.f. = 6).Conclusions: Our results suggest that Wolbachia has a protective effect to the larval stage of A. fraterculus when it is attacked by D. longicaudata, probably mediated by an enhancement in the immune system of the host larva which amplify its response against the parasitoid egg (i.e., encapsulation). However, physiological status of the host and changes in the beneficial microflora caused by the antibiotic treatment should be considered and further investigated. Currently, additional studies including the dissection of parasitized larvae and expression analysis of candidate genes involved in the immune response of the host are in progress.