Feeding behavior comparison of soybean aphid (Hemiptera: Aphididae) biotypes on different soybean entries

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), has become a major pest of soybean, Glycine max L. (Merr.), since it was first detected in Wisconsin in 2000. Three soybean aphid biotypes have already been documented in the United States in the first 10 years after its invasion. So far, there were a few studies done on feeding behavior of soybean aphid in United States. Electrical Penetration Graph (EPG) technique is a convenient and successful tool to study the feeding behavior of piercing and sucking insects in great detail. It is the first attempt to study the feeding behavior differences of biotype 1 and biotype 2 on soybean entries using the EPG technique. This study includes both resistant and susceptible entries from Kansas and Michigan. The starved aphids were attached to gold wire. The wired aphids then attached to a probing system, the whole system in turn attached to a computer. Aphids were placed on soybean plants at V1 stage and the circuit is completed when the aphids start probing. The experiments ran for 9 hrs each for the given channels. The graphs were saved on the computer hard disk, with 8 channels at a time. The result shows that the resistant and susceptible entries show significant differences in their EPG parameters, especially for the sieve element duration in both biotypes. But, no differences were found in any other probing phases between resistant and susceptible entries, except the number of potential drops (PDs) in biotype 2. Thus, it is concluded that resistance is largely associated with phloem tissues.