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Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 1/19/2012 Publication Date: 5/1/2012 Citation: Meagher Jr, R.L., Nagoshi, R.N. 2012. Differential feeding of fall armyworm (Lepidoptera: Noctuidae) host strains on a meridic and natural diets. Annals of the Entomological Society of America. 105(3):462-470. Interpretive Summary: The fall armyworm is a moth pest whose larvae attack various agricultural crops such as corn, forage grasses, turf, peanuts, and cotton in the southeastern, eastern and central United States. These moths are present all year in southern Florida, but they migrate northward during spring. Growers of sweet corn in southern Florida may apply over 20 insecticide applications per season to control this pest. Previous research has shown that the species is actually composed of two identical appearing strains. One strain prefers to feed and develop on corn and other large grasses, while the other strain prefers smaller grasses such as rice and bermudagrass. It is important to learn some of the biological and behavioral differences between these strains because they differ in their feeding on resistant plants and on their susceptibility to insecticides. Scientists at the USDA-ARS, Center for Medical, Agricultural and Veterinary Entomology, Gainesville, Florida, conducted laboratory experiments using laboratory colonies to determine if larvae from the two strains grow and develop equally on different host plants and an artificial diet. Results suggested that improvements need to be made in the identification of the host strains so that laboratory colonies can more realistically represent what is attacking crops in the field. These improvements will aid in the development of laboratory colonies that can be used to test a variety of control methods including resistant varieties. Technical Abstract: Fall armyworm, Spodoptera frugiperda (J. E. Smith) is a migratory, polyphagous species that attacks a wide variety of crops. The species is composed of two sympatric, morphological-identical host strains (corn and rice) that differ in their distribution on different host plants. Corn and rice strain colonies, characterized by Cytochrome oxidase I (COI) strain markers, were subjected to feeding studies using corn (Zea mays L.), stargrass (Cynodon nlemfuensis Vanderyst var. nlemfuensis ‘Florona’) and a meridic pinto bean diet. All colonies developed best on corn, producing larger larval weights and taking a shorter time to become pupae in the bioassays in 2005. Colony and strain differences were more pronounced with larvae reared on pinto bean diet or stargrass. Generally corn strain larvae grew larger and developed more quickly than rice strain larvae when fed pinto bean diet. These relationships were reversed on stargrass, where rice strain larvae displayed faster development both with respect to larval weight and larval duration. Additional bioassays conducted in 2010 showed fewer differences between host strains. A younger rice strain colony behaved similarly to the 2005 rice strain colonies while an older rice strain colony developed more similar to a corn strain colony. Regression analysis of larval duration versus larval weight showed that larvae from the different colonies appeared to obtain similar sizes and progress at similar rates when feeding on corn, but the rate of development was faster for rice strain larvae fed pinto bean diet than stargrass for each corresponding increase in larval weight. Limitations in the effectiveness of the COI marker to characterize host strains and the potential for unintended selection of corn strain traits when using a meridic diet are discussed. |
