Immune Response of Drosophila suzukii Larvae to Infection with the Nematobacterial Complex Steinernema carpocapsae–Xenorhabdus nematophila

Abstract

Entomopathogenic nematodes have been proposed as biological agents for the control of Drosophila suzukii, an invasive pest of small-stone and soft-skinned fruits. Larvae of the fly are susceptible to Steinernema carpocapsae infection but the reaction of immune defenses of the host are unknown. To determine the immune response, larvae were infected with S. carpocapsae and Xenorhabdus nematophila to evaluate the effector mechanisms of both humoral and cellular processes. The symbiont bacteria presented an inhibitory effect on the phenoloxidase cascade with a low level of melanization. Besides, X. nematophila activated the synthesis of putative antimicrobial peptides on the hemolymph of infected larvae. However, those peptides presented a lower antimicrobial activity compared to hemolymph from larvae infected with non-symbiont bacteria. Xenorhabdus nematophila avoided also the phagocytosis response of hemocytes. During in vitro and in vivo assays, S. carpocapsae was not encapsulated by cells, unless the cuticle was damaged with a lipase-treatment. Hemocyte counts confirmed differentiation of lamellocytes in the early phase of infection despite the unrecognition of the nematodes. Both X. nematophila and S. carpocapsae avoided the cellular defenses of D. suzukii larvae and depressed the humoral response. These results confirmed the potential of entomopathogenic nematodes to control D. suzukii.

Susceptibility of Drosophila suzukii larvae to the combined administration of the entomopathogens Bacillus thuringiensis and Steinernema carpocapsae

“…D. suzukii larvae native to Catalonia (NE Spain) were reared on a specific diet in laboratory 60 and maintained in a climate chamber at 25 °C, 45% relative humidity (RH), with a 12:12 h photoperiod. For each assay, only healthy larvae at the first stage (L1) of growth were used.…”

Drosophila suzukii Susceptibility to the Oral Administration of Bacillus thuringiensis, Xenorhabdus nematophila and Its Secondary Metabolites

“…D. suzukii larvae native to Catalonia (NE Spain) were reared on a specific diet [ 8 ] and housed in a climatic chamber at 25 °C and 45% relative humidity, with a 12:12 h photoperiod. Only healthy larvae in comparable growth stage (L1) were used for mortality trials and bioassays.…”

“…These nematocomplexes at the infective juvenile (IJ) stage can penetrate the target insect inside the infested fruit [ 6 , 7 ]. In some studies, in which immune defenses of the insect target have also been investigated [ 8 , 9 ], nematodes have been shown to be quite effective, although semi-field and field studies are very scarce [ 10 ]. Moreover, the isolated bacteria symbionts, Xenorhabdus spp.…”

The Two Faces of Nematode Infection: Virulence and Immunomodulatory Molecules From Nematode Parasites of Mammals, Insects and Plants

“…This immunomodulatory mechanism is swift enough to allow for the infection of not just the nematode, but its mutualistic bacterial co-infector Photorhabdus luminescens , which would otherwise be killed by its insect host. In a similar manner, S. carpocapsae suppresses the immune response of its Drosophila host, allowing for the propagation of the endosymbiotic bacteria Xenorhabdus nematophila ( Garriga et al, 2020 ). Shortly after infection, and before the bacteria is released from the gut of the infected nematode, there is a significant reduction in total insect hemocytes, suggesting that the nematode itself is capable of suppressing the host immune system, to the benefit of its endosymbiotic bacteria.…”