The diminutive natural enemies of invasive soybean aphidin the LTER

Brewer, M.J., T. Noma, and M. Kaiser

Presented at the All Scientist Meeting (2003-09-12 )

Soybean aphid (Aphis glycines) comes from China and was first sighted in the United States in July of 2000. Severe damage to soybean plants by this aphid has already been documented. Previous to this invasion there were few aphids feeding on soybean. While many other infested states are importing natural enemies in a biological control effort, Michigan has held off. It may be that native and previously introduced natural enemies of aphids which are already established in our area can adapt to soybean aphid. However nobody to date has performed an extensive and thorough search for early adaptation to this invading species. Natural enemies of aphids can occur in a diversity of habitats. Alfalpha in particular is known to be home to several species of aphid predators and parasitoids. To what degree can native and previously introduced natural enemies adapt to a new invader?:

To detect the presence of parasitoids and predatory flies that have been able to adapt to soybean aphid as a source of prey/hosts. We also seek signs of early adaptation to this invading species and evidence that there are enough natural enemies that can adapt to SBA already in place in the LETR system to allow for effective biological control of SBA. We also hope to gather enough information to propose some possible methods for conserving and augmenting these natural enemies of SBA.

SBA natural enemies were sampled 3 times, June through September. 80 pots of soybean infested with SBA were placed in different treatments in a field setting at KBS LTER main experimental site in 20 sets of four. The pots were divided into four of KBS’s treatments: At each sampling period for 2 days, pots were exposed to parasitoids and predatory flies of the SBA. The parasitoids oviposited in aphids and the flies oviposited on aphid-infested soybean foliage of the pots. After the two days of exposure the soybean plants were clipped and placed in emergence canisters to trap emerging adult parasitoids and predatory flies. This technique is more labor intensive than simply collecting soybean plants from the field, but allowed us to sample other habitats such as alphalpha.

We have detected a diverse assemblage of native or previously introduced natural enemies attacking SBA. In general diptheran predators seem to be more abundant early in the season, and hymenopteran parasitoids seem to be more abundant later in the season. Individual braconid species seem to be much more habitat selective than the aphelinids and diptheran predators

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