Biological control of leafminers: Mechanisms of ecological interactions between biocontrol agents

Interspecific interference and intraguild predation (IGP) between the biological control agents Steinernema carpocapsae and Diglyphus begini have been found. Nematode infective juveniles (IJs) were able to infect D. begini larvae in petri dishes and intact leaf mines. The presence of nematodes in mines with wasp eggs decreased the chance of wasp survival to adulthood. However, adult wasps were not susceptible to nematode infection, adult wasps detected and avoided ovipositing on nematode-infected leafminer larvae, and these nematode-infected larvae served as host-feeding sources for the wasps. In addition, leafminer larvae parasitized by the wasp had decreased susceptibility to nematode infection.; In field trials on gerbera under partial biological control by D. isaea, applications of IJs resulted in a significant decrease in live leafminers. Observed nematode infection of leafminer larvae was low, but a significantly higher percentage of mines were found to be empty in the nematode treatment than in the control, possibly due to rupture of the 1 st instar leafminers after nematode penetration. This would result in a higher nematode infection rate than initially observed. No nematode infection of parasitoid larvae was observed. These results demonstrate that the use of S. carpocapsae for leafminer control in the presence of Diglyphus parasitoids increases leafminer mortality and has no impact on the parasitoids.; Dipping leafminer-infested chrysanthemum plants a nematode suspension was more effective than spraying the plants. While spraying plants with the nematode suspension was not as effective as dipping, the level of control achieved by spraying varied with leafminer density. Spraying was more effective at higher leafminer densities, while there was no relationship between mortality and leafminer density for dipped plants.; The foraging behavior of S. carpocapsae has been described as “ambushing”, in that it rarely moves towards a host-source, but rather waits for a host. S. feltiae populations, on the other hand, tend to have a higher proportion of “cruisers”, which actively seek out hosts. Although a higher proportion of S. feltiae IJs than S. carpocapsae IJs would be expected to orient towards host-cues, the opposite was found to be true.