Effects of Regional Releases of Resistant Wheats on the Population Dynamics of the Cereal Leaf Beetle (Coleoptera: Chrysomelidae)1

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Abstract
During a 5-year pilot program, two pubescent (hereafter referred to as “resistant”) winter wheat varieties, ‘Fuzz’ (CI17412) and ‘Downy’ (CI17421), gradually replaced the less pubescent (hereafter referred to as “susceptible”) winter wheat varieties grown in a 4 mi square (6.4 km × 6.4 km) in Berrien County, Mich. As this shift in the proportion of resistant (pubescent) winter wheats planted in the area occurred, the population dynamics of the cereal leaf beetle, Oulema melanopus (L.), was monitored to evaluate the effects. Presence of adults in oats, susceptible wheat, and resistant wheat was unaffected by the increase in the proportion of wheat acreage sown with resistant wheat. As the proportion of wheat acreage sown with resistant wheat increased, adult CLBs were not forced into oats as expected, but utilized the resistant wheat by taking advantage of the within- and between-plant variation in pubescence. Leaf pubescence was associated with a significant reduction in oviposition in wheat; oviposition was highest in oats. In direct comparisons between resistant and susceptible wheats, no significant differences were observed in egg survival, egg parasitism by Anaphes flavipes (Foerster), or larval parasitism by either Tetrastichus julis (Walker) or Diaparsis temporalis Horstmann.