ABILITY OF OLDER CRYPTOLESTES-FERRUGINEUS (COLEOPTERA, CUCUJIDAE) LARVAE TO INFEST WHOLE CORN AND LONG-TERM POPULATION-GROWTH ON WHOLE CORN

The rusty grain beetle is a cosmopolitan pest of stored products, and may cause grain to spoil and heat. The ability of 2-week-old rusty gra in beetle larvae, Cryptolestes ferrugineus (Stephens), to complete dev elopment to the adult stage on undamaged corn kernels was compared wit h development on damaged kernels (undamaged kernels that are slit thro ugh the germ with a razor blade) and coarsely cracked corn at 30-degre es-C and 75% RH. Both the condition of the corn and infestation level (1 or 5 larvae per cage) significantly affected the proportion of samp les in which adults developed. More adults developed in samples contai ning damaged or coarsely cracked corn than in samples containing undam aged corn. More adults were produced in samples at the higher infestat ion level. The results indicate that older rusty grain beetle larvae c an complete development on sound grain, but more complete development on damaged grain. A long-term test of the ability of rusty grain beetl es to infest whole corn was also conducted. Ten adults and ten 2-week- old larvae were placed on 150 g each of. 1) undamaged kernels, 2) dama ged kernels, 3) kernels that were sifted to remove dockage but not oth erwise selected, and 4) coarsely cracked corn. Population growth at 30 -degrees-C and 75% RH was monitored over a 36-week period. Population growth on coarsely cracked corn was rapid. This treatment was terminat ed after 20 weeks, because the corn was deteriorating and population g rowth was beginning to decline. Final population levels on damaged and unselected com kernels were high. There was little population growth on undamaged kernels. The results indicate that sound grain is relativ ely resistant to infestation by rusty grain beetles, even when older l arvae are present. Although commercial grain is susceptible to infesta tion, rate of rusty grain beetle population growth is slow compared to that on damaged grain.