HOST FINDING AND FEEDING BEHAVIOR OF WESTERN CORN ROOTWORM LARVAE (DIABROTICA, CHEMOTAXIS, INFESTATION)

SVEN PAVEL STRNAD, Purdue University

Abstract

Field and laboratory studies were conducted to determine the ability of corn rootworm larvae to locate and infest corn roots. Responses of first-instar western corn root to CO(,2) and N(,2) gas gradients were studied in a laboratory test arena. Larvae exhibited a positive chemotactic response to CO(,2) but not N(,2) or air. There was no indication that a kinesis of any type was involved because velocities and turning rates were not significantly different among treatments. Results indicate that newly hatched larvae may use CO(,2) to locate corn roots. Horizontal and vertical movement of first-instar western corn rootworms were studied in a 30-cm soil chamber filled with silt loam, sandy loam, or sand at various bulk densities. In all noncompacted soils, >80% of the larvae moved at least 25 cm toward the CO(,2) source. Increases in the soil bulk density inhibited larval movement to varying degrees. More upward rather than downward movement occurred. Results indicate that newly hatched WCR larvae move rapidly over long distances (>25 cm) in loosely packed soil and can direct this movement to a CO(,2) source. Movement is reduced in soil bulk densities approaching those in the field at planting time. The distribution of corn rootworm larvae in corn roots was mapped through the larval period in three different plantings of corn in 1984 and 1985. Two additional dates were sampled each year during the hatch period. The roots were carefully extracted by hand from the soil and boiled in a solution of lactophenol and acid fuchsin to fix and stain the larvae. First-instar larvae were found in the seminal roots as well as roots on the first 5 whorls. Significantly more first- and second-instars were oriented toward the root tip than the root base. Also, significantly more than 33% of the first and second instars were present in the distal third of a root. Second-instars tended to be closer to the plant base than the first-instar larvae, but not as close as the third-instar larvae. Over time, larvae tended to move into the roots of the newer whorls.

Degree

Ph.D.

Subject Area

Entomology

COinS