Nursery, Greenhouse, and Landscape News

Japanese Beetles Avoid Fungus-treated Soil

Although pathogens such as Metarhizium anisopliae can cause high levels of insect mortality in laboratory experiments, population control from field applications are often less effective. Previous work has shown that soil physical properties can affect the persistence and spatial interactions of soil insects and fungal pathogens in soil. Japanese beetle females discriminate among oviposition sites differing in soil texture, soil moisture, and organic matter, and the grubs are capable of moving throughout the soil in response to many factors. How the fungus affects beetle behavior in turf and soil had not been studied before.

The effect of mycelial and conidial formulations of M. anisopliae on the survival and behavior of Japanese beetle larvae and ovipositing adults was explored in several greenhouse experiments. Changes in grub feeding site selection on sod roots, movement patterns and survival in fungus-inoculated soil were examined. The effect of fungus particles on oviposition was also studied in the lab.

The application of mycelial particles in soil affected the behavior of both larval and adult beetles. Grubs avoided soil that contained high concentrations of the fungus for up to 3 weeks after application. There was minimal movement of the fungus in the soil, so the grubs could easily move to untreated areas, resulting in low mortality.

However, incorporation of fungus increased egg laying by adult beetles. Females presented with a choice between soil with and without fungal mycelium consistently deposited more eggs in soil containing the fungus. This increased egg laying may help to offset later grub mortality that would presumably occur in fungus-containing soil.

Although soil physical properties may indirectly affect fungal performance, these results may help explain some of the inconsistency in results that often occur when fungal pathogens are used to control insects in the field.

Source:

Villani, M. G., S. R. Krueger, P. C. Schroeder, F. Consolie, N. H. Consolie, L. M. Preston-Wilsey, and D. W. Roberts. 1994. Soil application effects of Metarhizium anisopliae on Japanese beetle (Coleoptera: Scarabaeidae) behavior and survival in turfgrass microcosms. Environ. Entomol. 23(2): 502-513.

A Tachinid Fly Parasite of Japanese Beetle

Istocheta (=Hyperecteina) aldrichi is a tachinid fly native to central and northern Japan that parasitizes adult Japanese beetles. It was first introduced in the United States in 1922.

I. aldrichi overwinters in a puparium within the body of the dead host in the soil. The adult flies appear from mid-June to mid-July in New Jersey and feed on aphid honeydew and nectar. The females attach an egg on the thorax of newly emerged beetles. Each female can deposit up to 100 eggs over a 2 week period. The egg hatches in 24 hours and the maggot burrows into the body cavity of the beetle to feed internally. The larvae kill the beetles in about 5-6 days (compared to the 4-6 week life span of a non-parasitized adult), during which time the beetles bury themselves in the ground.

Because the fly kills the beetle so rapidly, a large portion of the female beetle population, especially those emerging early, are killed before they are able to deposit their first eggs. However, because the fly is not well synchronized with its host in the U.S. -- the flies emerge several weeks before the beetles do-- I. aldrichi only affects the first emerging beetles and disappears long before the peak of beetle emergence is reached.

During the 1930's and 40's this fly was of only minor importance, but by the late 1970's was found to be parasitizing about 20% of the adult Japanese beetles in Connecticut.

- Susan Mahr, University of Wisconsin


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