Submitted to: Biocontrol
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/11/2010
Publication Date: 8/29/2010
Citation: Riddick, E.W., Wu, Z. 2010. Lima bean – lady beetle interactions: hooked trichomes affect survival of Stethorus punctillum larvae. Biocontrol. 56:55-63. Interpretive Summary: The mite-eating lady beetle Stethorus punctillum is one of the most important natural enemies commercially available for augmentation biological control of pest mites, such as the two-spotted spider mite Tetranychus urticae. We found that epidermal hairs (hooked trichomes) on Lima bean (Phaseolus lunatus) plants had a detrimental effect on the survival of S. punctillum larvae but not adults. Both nymphs and adults of the pest mite T. urticae were unaffected. This study shows that trichome-based resistance in Lima bean has more of an effect (albeit, negative) on a mite-eating predator than on a plant-feeding mite.
Technical Abstract: We tested the hypothesis that Lima bean Phaseolus lunatus L. (Henderson cultivar) trichome density affects the survival of the acariphagous lady beetle Stethorus punctillum Weise. When isolated throughout larval development, 10% or less of S. punctillum larvae reared on two-spotted spider mite Tetranychus urticae Koch on small P. lunatus leaves survived until pupation. Trichome density (i. e., number of hooked trichomes per cm) was greatest on the underside of small leaves and least on large leaves, indicating that survival rate increased as trichome density decreased. Hooked trichomes impaled S. punctillum larvae more often at the apex of the abdomen than at any other body part. Hooked trichomes also trapped S. punctillum adults, but they always managed to free themselves. Hooked trichomes did not trap or impale spider mite nymphs or adults. This study highlights the discriminate effect of Lima bean trichomes on a predacious lady beetle and an herbivorous mite.