Abstracts Category : Other

Infestationof Rhyzopertha dominica first instars on different classes ofwheat

by Mario Andrada

The lesser grain borer, Rhyzopertha dominica (F.),females lay eggs loosely outside of wheat kernels. Larvae hatchingfrom eggs enter wheat kernels to complete immature development.Four laboratory experiments were conducted to understand the wheatkernel infestation by first instars of R. dominica at 28C and 65%r.h. The first experiment compared different kernel to first instarratios on sound hard red winter (HRW) wheat class, probability ofsuccessful infestation, and subsequent adult development asaffected by site of feeding on the kernels. Infested kernels weredissected 21 d after infestation to determine stage of developmentand larval weight. Development of larvae to adulthood was monitoredfor 50 d from time of infestation. Different kernel to first instarratios did not affect probability of infestation, entry sitepreferences, larval development and weight, and days to adultemergence. In the second experiment one first instar was placedwith a kernel on each of seven different wheat classes. Wheatkernels were artificially-damaged with a microdrill at the germ,endosperm, and brush end, and the sound kernels served as thecontrols. At 21 d, 82-90% of artificially-damaged HRW wheat kernelswere infested by larvae versus 12% for sound kernels. Five timesfewer hard white (HW) wheat sound kernels were infested by larvaecompared with infestation in soft white (SW) wheat kernels. Soundkernels of durum, soft red winter (SRW), hard red spring (HRS), andhard white spring (HWS) wheat classes were more resistant to larvalinfestation than artificially-damaged kernels. Majority of firstinstars preferred germ as the entry site on HRW, HWW, SRW, and HWSwheat classes. Germ entry promoted faster larval development,leading to heavier larvae, and higher kernel weight losses. Adultemergence was earlier by 3-7 d compared with other sites across all6 wheat classes, except for SWW class, where adult emergence wasnil at 50 d. In the third experiment, speed of larval developmenton artificially-drilled HRW wheat kernels on different kernelsites. Three-hundred kernels each were drilled near the germ,endosperm, and brush end, and one first instar was placed perkernel in a glass vial. Kernels from glass vials were dissectedevery 3 d for 30 d and larval head capsule was measured. Larvaldevelopment was fastest on the germ, followed by endosperm, andbrush end. In the fourth experiment short-term feeding by R.dominica adults on infestation by first instars on sound wheatkernels was determined. Two laboratory tests were conducted withsingle and grouped (10) kernels using either two adults or twofirst instars per kernel. Signs of feeding were monitored for 21 din single kernels and 7 d in grouped kernels. There was asignificant association between adult feeding and larvalinfestation responses in single and group kernel tests. Inconclusion, understanding factors that contribute to first instarestablishment in wheat kernels will have impacts in breedingvarieties that could be resistant and designingAdvisors/Committee Members: Subramanyam Bhadriraju.