Multifaceted effects of host plants on entomopathogenic nematodes

Authors: HAZIR, SELCUK - Adnan Mederes University; Shapiro Ilan, David; HAZIR, CANAN - Adnan Mederes University; LEITE, LUIS - Instituto Biologicio - Brazil; CAKMAK, IBRIHIN - Adnan Mederes University; Olson, Dawn

Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/16/2016
Publication Date: 2/24/2016
Citation: Hazir, S., Shapiro-Ilan, D.I., Hazir, C., Leite, L., Cakmak, I., Olson, D.M. 2016. Multifaceted effects of host plants on entomopathogenic nematodes. Journal of Invertebrate Pathology. 135:53-59.

Interpretive Summary: Overuse of chemical insecticides is harmful to humans and the environment, and therefore alternative environmentally friendly methods of insect pest control are desired. Beneficial nematodes are safe and natural bio-insecticides. These nematodes only attack insects. They enter the insects and kill them. Then the beneficial nematodes reproduce inside the dead insect, and thousands of new nematode progeny emerge to find new pests to attack. Interestingly, we discovered that the plant an insect feeds upon can affect the virulence (killing power) and reproduction of beneficial nematodes. Specifically, we observed that tobacco-fed corn earworm larvae were less susceptible to nematode infection than corn earworm larvae fed on tomato or eggplant. Probably, certain chemicals in the tobacco are inhibitive to the nematode life cycle. Surprisingly, even though tobacco-fed larvae are less conducive to nematode infection, the beneficial nematodes are more attracted to tobacco-fed larvae than larvae fed on other plants (like tomato or eggplant). The cause for this “fatal attraction” must be explored further. However, we also learned that the nematodes can overcome their problem - if the beneficial nematodes are reared on tobacco-fed larvae for multiple generations they can adapt and negative effects are no longer observed. Importantly, we conclude that the crop plant can affect beneficial nematode efficacy, and therefore the interaction between the plant, insect, and nematode should be considered when designing alternative pest management programs.

Technical Abstract: The success of parasites can be impacted by multi-trophic interactions. Here we investigate aspects of multi-trophic interactions in a system involving an entomopathogenic nematode (EPN), its insect host, and host plant. Novel issues investigated include the impact of tritrophic interactions on nematode foraging behavior, the ability of EPNs to overcome negative tritrophic effects through genetic selection, and interactions with a fourth trophic level (nematode predators). We tested infectivity of the nematode, Steinernema riobrave, to corn earworm larvae (Helicoverpa zea) in three host plants, tobacco, eggplant and tomato. Tobacco reduced nematode virulence and reproduction relative to tomato & eggplant. However, successive selection (5 passages) overcame the deficiency. Despite the loss in virulence and reproduction nematodes, first passage S. riobrave was more attracted to frass from insects fed tobacco than insects fed on other host plants. Therefore, we hypothesized the reduced virulence and reproduction in S. riobrave infecting tobacco fed insects would be based on a self-medicating tradeoff, such as deterring predation. We tested this hypothesis by assessing predatory success of (Sancassania polyphyllae and Sinella curviseta) on nematodes reared on tobacco-fed larvae versus those fed on Galleria mellonella, tomato fed larvae, or eggplant fed larvae. No advantage was observed in nematodes derived from tobacco fed larvae. In conclusion, our results indicated that insect-host plant diet has an important effect on nematode foraging, infectivity and reproduction. However, negative host plant effects, might be overcome through directed selection. We propose that host plant species should be considered when designing biocontrol programs using EPNs.