INTERACTIONS AMONG THE RUSSIAN WHEAT APHID, PAECILOMYCES FUMOSOROSEUS AND THE CONVERGENT LADYBIRD

Authors: PELL, K - INST FOR ARABLE CROPS RES; Vandenberg, John

Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2002
Publication Date: 4/1/2002
Citation: PELL, K.K., VANDENBERG, J.D. INTERACTIONS AMONG THE RUSSIAN WHEAT APHID, PAECILOMYCES FUMOSOROSEUS AND THE CONVERGENT LADYBIRD. BIOCONTROL SCIENCE AND TECHNOLOGY. 2002. v. 12. p. 217-224.

Interpretive Summary: The Russian wheat aphid (RWA) is a worldwide pest of wheat and barley. It was first found in the United States in the mid-1980s. Since then, it has caused a combined direct and indirect economic impact in excess of $1 billion. The fungus Paecilomyces fumosoroseus has potential as a safe and effective biological control agent for this aphid, but information is needed about how it interacts in the field with other natural enemies of RWA. The convergent ladybird beetle is an efficient aphid predator widespread in the U.S. The interactions among RWA, the beetle and the fungus were tested in various ways. A low percentage of adult beetles became infected when exposed to very high fungus doses. Beetles will not feed on infected aphids and thus will not limit the spread of the fungus. Beetle adults successfully vectored the fungus, particularly when foraging in the presence of infected aphids. These findings will facilitate deployment of these two natural enemies as aphid control agents.

Technical Abstract: Paecilomyces fumosoroseus is under development as a mycoinsecticide for control of the Russian wheat aphid. Interactions with other natural enemies within the agro-ecosystem, such as Hippodamia convergens, require evaluation before its potential can be realized. In laboratory bioassays H. convergens adults were sprayed with suspensions of P. fumosoroseus conidia at different concentrations and mortality assessed. Although a small proportion of ladybirds succumbed to infection it is unlikely that they would be at risk from infection as a direct result of a spray application in the field. When provided with uninfected or P. fumosoroseus-infected aphid cadavers as prey, ladybirds consumed more uninfected aphids. The predators never consumed aphid cadavers from which the fungus was erupting or sporulating. Hippodamia convergens is, therefore, unlikely to be a significant intraguild predator of P. fumosoroseus. Predators contaminated with conidia of P. fumosoroseus were able to vector conidia to healthy aphid populations and initiate infection in a proportion of those aphids. The proportion of aphids becoming infected was greatest when the ladybirds became contaminated when foraging amongst sporulating cadavers. Depending on the contamination method, some ladybirds also succumbed to infection under these conditions.