Submitted to: Southern Nursery Association Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 2/8/2000
Publication Date: N/A
Citation: Interpretive Summary: The movement of the Japanese beetle to uninfested areas of the US is a great concern because it can be spread through several avenues including the movement of nursery stock. The effect of some of present day insecticide treatments on natural enemies of Japanese beetle is not known, although studies have shown that broad-spectrum insecticides applied to turfgrass can reduce beneficial invertebrates like the Spring Tiphia. This wasp has recently been found in Ohio, North Carolina, Indiana and Tennessee where it develops externally on a Japanese beetle grub ultimately killing and consuming it. The wasps search for grubs in the late spring, which could coincide with applications of the insecticides Marathon (imidacloprid) and Mach2 (halofenozide) that target early instars of the Japanese beetle. Our objectives were to see if exposure to either chemical insecticide would affect the ability of the wasps to parasitize Japanese beetle grubs, or the ability of the wasp larvae to form cocoons. We found that exposing Japanese beetle grubs or wasp adults to either Marathon or Mach2 did not have a negative impact on the parasites laying eggs or the development of wasp larvae to the cocoon stage. These results are important to the nursery industry in its efforts to develop both IPM programs for insect suppression and quarantine treatments to allow movement of plant products. New chemistry insecticides which eliminate Japanese beetle larvae, but do not have a negative effect on natural enemies, are important in conserving parasite populations.
Technical Abstract: No information is available on the effect on natural enemies of the Japanese beetle, Popillia japonica, from new insecticides such as Marathon (imidacloprid) or Mach2 (halofenozide) being used for control of the early instars of white grubs. Previous studies have shown that broad-spectrum insecticides applied to turfgrass can reduce the abundance and diversity of beneficial invertebrates and predators. The Spring Tiphia, Tiphia vernalis (Hymenoptera: Tiphiidae), is a wasp that searches for grubs in the late spring, which could coincide with applications of the insecticides that target early instars of Japanese beetle. Our objective was to determine if exposure to either Marathon or Mach2 would affect the ability of T. vernalis to parasitize Japanese beetle grubs or the ability of the parasite larvae to develop. Overall, exposing either the beetle grubs or Tiphia adults to either Marathon or Mach2 for 4 days did not have a negative impact on parasitisation. These results, although preliminary, indicate that neither Marathon or Mach2 would prevent parasitism of the Japanese beetle, nor development of the Tiphia parasite to the cocoon stage. More tests are necessary to determine the effect of insecticide exposure for longer periods of time as well as the effect on the emergence of Tiphia adults.