The modulation effect of the Steinernema carpocapsae - Xenorhabdus nematophila complex on immune-related genes in Drosophila suzukii larvae.

Larvae of the invasive pest Drosophila suzukii are susceptible to the Steinernema carpocapsae - Xenorhabdus nematophila complex and an assessment of the immune-regulatory system activation in this insect was performed to understand the response to the nematode infection. The expressions of 14 immune-related genes of different pathways (Imd, Toll, Jak-STAT, ProPO, JNK, TGF-ß) were analyzed using qRT-PCR to determine variations after nematode penetration (90 min and 4 h) and after bacterial release (14 h). Before the bacteria were present, the nematodes were not recognized by the immune system of the larvae and practically none of the analyzed pathways presented variations when compared with the non-infected larvae. However, after the X. nematophila were released, PGRP-LC was activated leading to the gene upregulation of antimicrobial peptides of both the Toll and Imd pathways. Interestingly, the cellular response was inactive during the infection course as Jak/STAT and pro-phenoloxidase genes remained unresponsive to the presence of both pathogens. These results illustrate how D. suzukii immune pathways responded differently to the nematode and bacteria along the infection course.

Compatibility of entomopathogenic nematodes with fipronil.

The survival and infectivity of infective juveniles (IJs) of three species of entomopathogenic nematodes, Steinernema carpocapsae Weiser, S. arenarium (Artyukhovsky) (Rhabditida: Steinernematidae) and Heterorhabditis bacteriophora Poinar (Rhabditida: Heterorhabditidae), were determined after exposure to different concentrations (250, 500, 1000 and 2000 ppm) of fipronil, an insecticide acting on the GABA receptors to block the chloride channel. Heterorhabditis bacteriophora was very tolerant to all concentrations of fipronil, with the highest mortality of 17% being observed at 2000 ppm of fipronil after 72 h exposure. Steinernema carpocapsae showed a similar response, with the highest mortality of 11.25% of IJs being observed after 72 h exposure to 2000 ppm of fipronil. Steinernema arenarium was, however, more sensitive to fipronil, and at 2000 ppm mortality rates of 94.6% and 100% were observed after 24 and 72 h, respectively. Fipronil had negligible effects on the infectivity of the three nematode species tested. The IJs which survive exposure to all concentrations of fipronil tested can infect and reproduce in Galleria larvae. The moderate effects on entomopathogenic nematodes of a lower fipronil concentration (250 ppm) and the field rates (12-60 ppm) of fipronil used as insecticide, suggest that direct mixing of entomopathogenic nematodes and fipronil at field rates is a viable integrated pest management option.

Natural Occurrence of Entomopathogenic Nematodes (Rhabditida: Steinernematidae and Heterorhabditidae) in Spanish Soils

Entomopathogenic nematodes (Steinernematidae and Heterorhabditidae) were surveyed in Spanish soils using the Galleria baiting technique. A total of 750 soil samples were taken from 150 sites representing different regions and habitat types (cropland, woodland, and pasture). Entomopathogenic nematodes were recovered from 35 sites; 33 sites were positive for the occurrence of steinernematids and 2 sites for heterorhabditids. Five distinct morphological types of steinernematids were recovered: Steinernema feltiae (Filipjev), Steinernema carpocapsae (Weiser), Steinernema affinis (Bovien), and two other Steinernema spp. Heterorhabditis bacteriophora Poinar was the only species of this family isolated in this survey. S. feltiae was the most common species found (23 sites). There was not a significant association between sampling time (spring/autumn) and frequency of nematode recovery. Nematodes were isolated from coastal areas (0 m elevation) to high altitude areas (2000 m). Annual median temperature and rainfall had little association with the presence of nematodes. Soil moisture and temperature regimes are more important factors in determining the prevalence of these entomopathogenic nematodes. They were associated with soils with udic moisture regimes and cryic temperature regimes. Nematodes were more frequently recovered from cropland soils than from woodland and pasture soils, but differences between habitat type were not significant.