Suppression of aphids by augmentative release of larvae of flightless Harmonia axyridis

The release of the larvae of flightless ladybird beetles could extend the duration of effective control because of the longer presence of adult stages, and the per individual production cost for juvenile stages is lower than that for adult stages. A preliminary release experiment was conducted to assess the effectiveness in controlling two aphid species, Aphis gossypii and Aulacorthum solani, using second instars of a flightless strain of Harmonia axyridis. The number of A.gossypii was suppressed in greenhouses that contained the flightless strain compared with greenhouses that contained the wild-type strain. In one of two replicates, more flightless adults were observed on the plants for longer than wild-type adults. However, it was not clear whether the extension of the residence period contributed to the effectiveness in controlling aphids directly, because the population of ladybirds in the greenhouses consisted of both larvae and adults during parts of the experimental period. In flightless H.axyridis, the release of larvae was more effective in suppressing A.solani than the release of adults. These results suggest that it may be more effective to release larvae of flightless H.axyridis than wild-type larvae or flightless adults.