Time and frequency of applications of entomopathogenic nematodes and their persistence for control of western flower thrips Frankliniella occidentalis

Post application persistence of two entomopathogenic nematode (EPN) species, Heterorhabditis bacteriophora strain HK3 and Steinernema carpocapsae strain DD136, was studied against soil-dwelling late second instar larvae (L2) of western flower thrips (WFT) Frankliniella occidentalis (Thysanoptera: Thripidae). The nematodes were applied at 200 and 400 infective juveniles (IJ) cm−2, and L2 WFT were introduced at 0 (same day), 3, 6, 9 or 12 days after nematode application (DANA). Heterorhabditis bacteriophora caused higher thrips mortality than S. carpocapsae in most of the tests and both species persisted for at least 6 days, causing WFT mortality of up to 76 and 37.8%, respectively. In a separate experiment, H. bacteriophora and S. feltiae (Filipjev) Sylt were applied at 200 and 400 IJ cm−2 once (10, 15, or 20 days) or twice (10 and 15, 10 and 20, or 15 and 20 days) after introduction of ten female and two male WFT adults onto bean plants (Phaseolus vulgaris). An early repeated application (10 and 15 days after adult WFT release) of H. bacteriophora at 200 IJ cm−2 resulted in significantly lower numbers WFT than a single applications at 400 IJ cm−2 indicating that better WFT control can be achieved if the same concentration is split over time. However, an early application (10 days after adult WFT release) of H. bacteriophora at 400 IJ cm−2 controlled WFT better than late applications, indicating that time of EPN application is additionally very crucial in WFT control. For S. feltiae, higher WFT mortality was recorded when nematodes were repeatedly applied on days 10 and 15 than in any other applications at a given concentration. Thus, an early application of an efficient and relatively more persistent nematode species, e.g., H. bacteriophora HK3, at a lower concentration but in a repeated manner, can result in higher thrips control than a single application at the higher concentration.