Ability of Older Cryptolestes ferrugineus (Coleoptera: Cucujidae) Larvae to Infest Whole Corn and Long-Term Population Growth on Whole Corn2

Abstract

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 grain beetle larvae, Cryptolestes ferrugineus (Stephens), to complete development to the adult stage on undamaged corn kernels was compared with development on damaged kernels (undamaged kernels that are slit through the germ with a razor blade) and coarsely cracked corn at 30°C and 75% RH. Both the condition of the corn and infestation level (1 or 5 larvae per cage) significantly affected the proportion of samples in which adults developed. More adults developed in samples containing damaged or coarsely cracked corn than in samples containing undamaged corn. More adults were produced in samples at the higher infestation level. The results indicate that older rusty grain beetle larvae can complete development on sound grain, but more complete development on damaged grain. A long-term test of the ability of rusty grain beetles 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) damaged kernels, 3) kernels that were sifted to remove dockage but not otherwise selected, and 4) coarsely cracked corn. Population growth at 30°C and 75% RH was monitored over a 36-week period. Population growth on coarsely cracked corn was rapid. This treatment was terminated after 20 weeks, because the corn was deteriorating and population growth was beginning to decline. Final population levels on damaged and unselected corn kernels were high. There was little population growth on undamaged kernels. The results indicate that sound grain is relatively resistant to infestation by rusty grain beetles, even when older larvae are present. Although commercial grain is susceptible to infestation, rate of rusty grain beetle population growth is slow compared to that on damaged grain.