Cereal Leaf Beetle:1 Larval Feeding, Orientation, Development, and Survival on Four Small-Grain Cultivars in the Laboratory2

Abstract

‘Hudson’ barley, ‘Clintland 64’ oats, ‘Genesee’ wheat and CI 8519 wheat (density and length of whose trichomes were considerably greater than those of the other three cultivars) served as food for larvae of cereal leaf beetle, Oulema melanopus (L.). However, on CI 8519 wheat, developmental time was longer, larvae consumed less food, and fewer insects survived. Thus, CI 8519 wheat appears to act as a physical deterrent to the larvae. An analysis of the fecal material of the first and fourth instars feeding on CI 8519 showed that trichomes, though ingested, were not digested and that first instars had to bite through most of the trichomes about three times before they could feed on the nutritious adaxial cells; fourth instars ate 72.5% of the trichomes whole, so they reached adaxial surface with the first bite. Since undigested trichomes are not flexible, some larvae may die from trichomes that penetrate the midgut epithelium. The mean percentage of all food consumed by each instar was: (1) 3.9; (2) 12.0; (3) 32.4; and (4) 51.7. When first-stadium feeding equivalents were designated as 1.00 and used as a basis for comparing feeding by fourth instars on each host, fourth instars consumed 10.8× (Hudson barley), 12.5× (Clintland 64 oats or Genesee wheat) and 16.5× (CI 8519) more than the respective first instars. Correlations between feeding of males or females and the length of the adult elytra or the adult weight were poor, but insects that consumed most food had a tendency to weigh more.