Seed infestation of Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) first instars on sound and artificially-damaged hard white winter and soft red winter wheat kernels

Little is known about wheat kernel infestation by first instars of Rhyzopertha dominica (F.), the lesser grain borer. Laboratory experiments were conducted to understand probability of infestation of wheat kernels by first instars and the resulting weight loss caused by developing larva within kernels. Fifty individual, sound, non-organic hard white winter (HWW) and soft red winter (SRW) wheat kernels were infested with one first instar of R. dominica at 28ºC and 65% r.h. Successful infestation was confirmed by dissecting kernels 21 days after infestation. Sound HWW wheat kernels had 10% infestation while SRW had 26%. Artificially-damaged kernels at the brush end, endosperm, and germ portions registered higher ranges of percentage of infestation for SRW (82-84%) classes compared with HWW (30-72%). First instars preferred the germ as site of entry for SRW and brush end for HWW. However, on both wheat classes, first instars entering through germ developed faster and were in the pupal stage compared with other entry sites. Mean larval head capsule width was greater when first instars entered through germ compared with other kernel portions. The weight loss measured at 50 days was 19-21% for HWW and SRW. These findings indicate that R. dominica first instars preferred germ as the site of entry, damaged wheat had higher infestation rates than sound kernels, and kernel weight loss was greater when larvae entered the germ portion because of faster development.

Key words: Wheat, lesser grain borer, first instar, nutritional ecology