Effects of Soybean Aphid Resistance on the Lady Beetle Harmonia axyridis Mediated by the Soybean Aphid Aphis glycines
Abstract
Plants can directly and indirectly influence the natural enemies of their herbivores. Such
trophic level effects apply to plants in natural and agronomic settings as well as to plants
bred for pest resistance and biological control of herbivores. The effects of host plant
resistance on herbivore natural enemies are highly variable, depending on the system.
Currently, there is great interest in breeding soybean for resistance to the soybean aphid
(Aphis glycines Matsumura). However, little is known about the effects of soybean aphid
resistance traits on soybean aphid natural enemies. This study looks at the indirect effects
of plant resistance to soybean aphid on the lady beetle Harmonia axyridis Pallas
(Coleoptera: Coccinellidae ), an important natural enemy of the soybean aphid, using seven
soybean varieties that exhibited variable resistance 1o the soybean aphid. Aphids were
collected from greenhouse-reared soybean plants and fed to beetles in the laboratory.
Harmonia. axyridis larval development time, adult mass, and fecundity over a month were
measured. Results indicated moderate and inconsistent indirect effects with highly
resistant plant varieties while some moderately-resistant plant varieties reduced adult
weight and egg production. My conclusion is that soybean aphid resistance is potentially
compatible with H. axyridis biological control, but care must be taken when selecting
varieties if there is more than one source of resistance or if plant resistance differentially
affects soybean aphids and their natural enemies.