Developmental Activities and Behavior of the Rice Weevil Inside Wheat Kernels12

Abstract

Fifty-five wheat kernels infested by Sitophilus oryzae (L.) were X-rayed daily to study egg-to-adult development and behavior within the kernels. Enlarged photographic prints (2530) prepared from the radiographs were examined to determine larval instars. Larval-tunnel widths in the daily radiographs were measured, as were head-capsule widths of other larvae from dissected kernels. Four increases in tunnel width occurred, each followed by 1–4 days of static tunnel width (assumed to be time of molting). Four corresponding increases in width of the larval head capsule were observed confirming results obtained by radiographing. The mean tunnel widths for the 4 instars were 0.31, 0.51, 0.83, and 1.34 mm; the means for stadia 1 through 4 were 3.9, 5.4, 4.7, and 5.1 days, respectively. Prepupa, pupa, and pre-emerged adult stages averaged 1, 5.2, and 4.6 days, respectively. The mean life cycle (including 4 days for oviposition) was 37 days. Of 23 adults which developed, 12 had pupal chambers on 1 side of the kernel, with most or all tunneling on that side, 7 constructed pupal chambers parallel to the crease but occupied portions of both kernel halves, and 4 located pupal chambers diagonally across the crease.