Evaluation of the nematodes Steinernema feltiae and Thripinema nicklewoodi as biological control agents of western flower thrips Frankliniella occidentalis infesting chrysanthemum.

摘要

In greenhouse studies, we evaluated a commercial formulation of the entomopathogenic nematode S. feltiae and the inoculative release of the thrips-parasitic nematode T. nicklewoodi against western flower thrips (WFT), F. occidentalis infesting potted chrysanthemums (Dendranthema grandiflora [D. morifolium]). Foliar sprays of S. feltiae applied at 1.25-2.5x103 infective juveniles (IJ) ml-1 and 1000-2000 l ha-1 at 3-day intervals alone (targeting feeding stages) or in combination with soil applications (simultaneously treating non-feeding stages in the soil at the same rates) decreased but did not provide adequate control of thrips in flowering plants artificially infested with a dense population. Similar nematode treatments applied for 4-5 applications at 6-day intervals in 2 batches of initially clean chrysanthemums failed to prevent unacceptable damage to flowers and leaves from a dense natural infestation within the greenhouse. Although some IJ survived up to 48 h within flowers and flower buds, few nematode-infected thrips (larvae and adults) were recovered. In studies with T. nicklewoodi (which is not amenable for mass production), the inoculative releases of two parasitized hosts per plant enabled the nematode to become established within existing WFT populations under greenhouse conditions. However, relatively poor transmission and slow speed of kill (nematode primarily suppresses populations through host sterilization) prevented low level inoculations, being effective over a single crop cycle. Further studies showed that transmission of T. nicklewoodi persisted for 9 host generations, infected up to 83% of adult thrips and provided long-term suppression of discrete caged populations, but only after uneconomically high thrips densities had been reached..