Title: Lima bean lady beetle interactions: spider mite mediates sublethal effects of its host plant on growth and development of its predator Authors
Submitted to: Arthropod-Plant Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 7, 2011
Publication Date: November 23, 2011
Citation: Riddick, E.W., Rojas, M.G., Wu, Z. 2011. Lima bean lady beetle interactions: spider mite mediates sublethal effects of its host plant on growth and development of its predator. Arthropod-Plant Interactions. 5(4):287-296. Interpretive Summary: The natural defenses that lima bean plants use to discourage insects and mites from feeding on their leaves may cause harm to natural enemies of plant pests. Spider mites cause economic damage to lima bean through their feeding on leaves. The lady beetle, Stethorus punctillum, is one of the most important natural enemies of spider mites. It is commercially available for reducing infestations of spider mites on vegetable, fruit, and nut crops in North America and Europe. To support efforts to produce this lady beetle commercially, our laboratory conducted experiments involving lima bean, two-spotted spider mite, and the lady beetle, S. punctillum. In this study, we show that natural defenses (cyanogenic compounds) in leaves of lima bean move up the food chain as spider mites extract nutrients from cells inside leaves. This movement of cyanogenic compounds is greater in one lima bean cultivar (Henderson) than in another (Fordhook). As a result, the lady beetle (S. punctillum) grows slower and is smaller-sized when eating spider mites on the Henderson cultivar. The cyanogenic compounds have no clear negative effect on the lifespan of lady beetle adults that eat spider mites on the Henderson cultivar. These compounds do not reduce the number of offspring that lady beetle females can produce. Identifying the ways that crop plants attempt to deter attacks from plant pests, and the potential effects that these defenses have on natural enemies of plant pests, is important to developing long-term, sustainable methods of protecting our crops.
Technical Abstract: Cultivated plants can have negative effects on natural enemies that attack spider mites. In this study, we tested the hypothesis that spider mites mediate effects of a lima bean, Phaseolus lunatus L., cultivar on the life history of a lady beetle Stethorus punctillum Weise. We provisioned laboratory arenas with two-spotted spider mites, Tetranychus urticae Koch, from planters containing Henderson Bush Bean or Fordhook 242 lima bean plants and monitored the growth, development, larval survival, fecundity, and adult lifespan of predators. We determined the protein content and the linamarin (a cyanogenic glycoside) content in foliage, spider mites, and predators. Predators took longer to develop and were smaller-sized when consuming mites from the Henderson foliage. There was no significant mite-mediated effect of cultivar on predator fecundity or lifespan. Although soluble protein was greater in foliage of the Henderson than the Fordhook cultivar, mites contained less protein when reared on the Henderson, and predators contained less protein when fed with mites from the Henderson. Linamarin content was greater in Henderson than Fordhook foliage, and greater in spider mites and predators in the Henderson treatment. Linamarin in Henderson foliage may reduce the ability of spider mites to utilize plant protein. As a result, prey quality is reduced and predators that feed on these prey (from the Henderson treatment) grow at a slower rate and are smaller-sized than their cohorts (from the Fordhook treatment). In conclusion, T. urticae mediates the effects of the Henderson cultivar on S. punctillum development but not fecundity or lifespan.