Synergism Between Natural Enemies and Biopesticides: a Test Case Using the Stinkbug Perillus bioculatus (Hemiptera: Pentatomidae) and Bacillus thuringiensis tenebrionis Against Colorado Potato Beetle (Coleoptera: Chrysomelidae)

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Sublethal effects of Bacillus thuingiensis on pests could synergize with natural enemies through extended larval development and reduced defense against predators. Mortality ranged from 18 to 76% for 4th instar Colorado potato beetles feeding on potato foliage dipped in M-Trak at 0.2-3.2 m1/liter H2O. Survivors resumed feeding in 48 h, but feeding was prolonged and time to pupation was extended 33-46%. Predation success by small nymphs of Perillus bioculatus was 40-77% on 4th instar potato beetle larvae that survived M-Trak exposure compared to only 3-40% on healthy 4th. instars. Thus, susceptibility to predation as well as extended development of larvae constitute mechanisms by which B. t. tenebrionis could synergize with predators in increasing mortality. This prediction was tested in 1994-1995 using field releases of P. bioculaturs followed by applications of low doses of B. t. tenebrionis. At rates of 1-4 per plant in both years, P. bioculatus destroyed 17-55% of potato beetle eggs compared to 1.6- 4.9% in control plots. In 1994, potato beetle larval mortality could not be related to rates of either control or their combination due to early P. bioculatus dispersal at low larval prey density. However, interaction between P. bioculatus and B. t. tenebrionis was significant in 1995 in combinations of P. bioculatus (1-2 per plant) and Novodor (2 liters/ha), the interactive effect causing 31% more larval mortality than expected from simple additive effects. The 2-yr field results indicate that synergism of B. tllllringiell8is with the egg-larval predator P. bioculatus in killing potato beetle larvae would critically depend on enough beetle eggs escaping predation to locally retain the predator during larval development..

Document Type: Research Article

Publication date: October 1, 1998

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