Non-target effects of exotic entomopathogenic nematodes?

Abstract: Entomopathogenic nematodes (EPN) have proven effective for the control of soildwelling life stages of agricultural insect pests. Steinernema feltiae, a globally ubiquitous EPN, is one such effective species. However, despite extensive surveying, it has not been found in southern Africa. Consequently, it was imported into South Africa to test its efficacy, particularly against the false codling moth, Thaumatotibia leucotreta, an important pest of citrus and other crops. This was met with opposition from a sector of agricultural scientists in South Africa, due to its perceived potential on-target effects. Their concern was twofold: potential displacement of populations of indigenous EPN; and its impact on non-target arthropods. Despite this, S. feltiae was applied on a trial basis in a few citrus orchards and found to effectively suppress the target pest, with efficacy sometimes surpassing that of the indigenous species, Heterorhabditis bacteriophora. Persistence was recorded for up to 7 months after application. However, surveys conducted at all sites more than a year later, revealed no further occurrence of S. feltiae. Furthermore, three independent surveys revealed the absence of naturally occurring EPN in 83 %, 93 % and 95 % of sampled agricultural soils, thus minimizing opportunities for displacement. Non-target effects against soil-dwelling arthropods were tested by pitfall trapping for 4 weeks before and after application of S. feltiae and H. bacteriophora. No significant decline in the numbers of individuals trapped from 16 different arthropod groupings was recorded. These findings underscore the already documented safety of exotic EPN.