Efficacy of entomopathogenic nematodes against Tuta absoluta.
Background: The South American tomato pinworm, Tuta absoluta (Meyrick) is one of the most serious insect pests of tomato plants. Current control strategies for T. absoluta primarily involve the use of insecticides, but increasing resistance in field populations has prompted research on alternative control measures. Biological control with entomopathogenic nematodes (EPNs) can be an alternative or one component of an Integrated Pest Management programme. In foliar application, EPNs encounter many factors that affect their survival and efficacy. This paper reports investigations into some of these factors for several EPN species; relative humidity (RH), temperature, time required by EPNs to enter a leaf and number of applications in whole leaf bioassays on tomato leaves. Results: RH was the most important factor; EPNs efficacy and survival decreased as RH declined. Steinernema feltiae was the most effective species followed by Steinernema carpocapsae then Heterorhabditis bacteriophora. Steinernema carpocapsae survived better at low RH than S. feltiae. The two Steinernema species induced similar mortality at 25°C, but S. feltiae was more virulent at lower temperatures (15 and 20°C) while S. carpocapsae was more virulent at higher temperatures (30 and 35°C). First and second instar larvae of T. absoluta required more applications compared to third and fourth instar larvae. Conclusion: The species of EPN used to control T. absoluta requires careful selection in relation to the temperature and relative humidity environment of the crop to maximise efficacy.