Seasonal abundance of thrips (Thysanoptera) on winter small grains in Georgia

Thrips species composition and seasonal abundance were studied in winter wheat, Triticum aestivum L., and winter rye, Secale cereale L., during 3 seasons in the coastal plain region of Georgia. Thrips abundance also was examined in wild radish, Raphanus raphanistrum L., a common annual winter weed in small-grain herds. Limothrips cerealium, (Haliday) and Frankliniella fusca (Hinds) were the 2 dominant species comprising >89% of the adult thrips collected in both crops. Frankliniella tritici (Fitch), F. bispinosa (Morgan), F. occidentalis (Pergande), F. williamsi Hood, Haplothrips graminis Hood and Plesiothrips perplexus (Beach) also were collected in low members in most years. Winter rye supported breeding populations of F. fusca during the autumn, winter, and early spring. Few thrips of any species were collected in winter wheat before spike emergence in March. However, large numbers of F. fusca and L. cerealium developed in wheat during the spring. Winter rye also served as a spring host for these thrips, but population increases were limited by grazing and early crop destruction. Differences in F. fusca phenology between wheat and rye probably are related to crop planting time in that rye for grazing is planted approximately 6 wk earlier than wheat for grain production. Small grains grown for grain production presumably are planted too late for colonization by F. fusca in autumn. Although F. tritici, F. bispinosa, and F. occidentalis adults were present in the spring, these thrips probably did not breed extensively in wheat or rye. However, flowering wild radish in wheat fields supported large populations of F. tritici and F. occiclentalis in late winter and spring. Therefore, winter small grains, particularly wheat, are important sources of F. fusca and L. cerealium that attack summer hosts. Small grains are not a major source of other Frankliniella spp., except possibly F. williamsi, but wild radish within winter small grains probably is an important spring source of F. tritici and F. occidentalis.