Monday, December 10, 2007 - 8:53 AM

Feeding on corn seedlings by predaceous coccinellid larvae

Susan E. Moser,, James D. Harwood,, and John J. Obrycki, University of Kentucky, Department of Entomology, S-225 Agricultural Science Center-North, Lexington, KY

Zoophytophagy is an omnivorous activity that occurs when a primarily carnivorous species feeds on plant material. Plant feeding by beneficial predators may have negative consequences if the plant material has been chemically treated, contains toxins, or was transgenically altered. Although common in predaceous Hemiptera, zoophytophagy is a rarely studied phenomenon in aphidophagous coccinellids. This study quantified the likelihood of feeding on Bt and non-Bt corn seedlings by 3rd and 4th instar coccinellid larvae, the regularity of feeding events by 4th instars, and the effect of leaf feeding on development time and adult size. Both 3rd and 4th instar Harmonia axyridis and Coleomegilla maculata consume leaf tissue and 4th instars were significantly more likely to feed on corn seedlings. C. maculata larvae ingested leaf tissue more frequently than H. axyridis. When given access to corn seedlings daily, development time of 4th instar C. maculata increased following Bt-hybrid corn treatments compared to non-Bt corn treatments. Zoophytophagous feeding behavior is thought to sustain predators during times of low prey availability, and leaf tissue feeding by coccinellids has typically been attributed to their need for water. However, in this study, tissue feeding regularly occurred even though coccinellid larvae had constant access to water and an ad libitum supply of aphids. We suggest that the likelihood of zoophytophagous feeding behavior is influenced by the physiological state of the individual, in addition to the environmental conditions. Furthermore, laboratory results suggest that the assumption that aphidophagous coccinellids are strictly predaceous may not be accurate.

Species 1: Coleoptera Coccinellidae Harmonia axyridis (multicolored Asian lady beetle)
Species 2: Coleoptera Coccinellidae Coleomegilla maculata