|Legaspi, Jr, B|
Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/3/2001
Publication Date: 7/1/2001
Citation: Greenberg, S.M., Sappington, T.W., Legaspi, Jr., B.C., Liu, T.X., Setamou, M. 2001. Feeding and life history of Spodoptera exigua (Lepidoptera: Noctuidae) on different host plants. Annals of the Entomological Society of America. 94(4):566-575. Interpretive Summary: Beet armyworm (BAW) attacks more than 90 plant species in at least 18 families throughout North America, many of which are crop plants. Over the last two decades, BAW has become a destructive secondary pest of cotton in the USA. In 1998, a relatively mild year for BAW, 5.1 million acres of cotton in the USA were infested with BAW and total losses from this insect were $19.2 million. But in outbreaks, the cost of cotton yield losses was $371 per acre, and the cost of insecticides targeted at BAW was $44 per application per acre. Chemical control programs often lead to insect resistance and associated environmental problems. Development of efficient strategies for controlling BAW will require knowledge of the biological relationships between the host plant and insect. We studied the BAW larval consumption rates on cultivated crops (cabbage, cotton, and pepper) and widely distributed weeds (pigweed, Amaranthus spp., and wild sunflower); effects of consumption rate on pupal weights and the latter on fecundity; and effects of host plant on BAW reproduction potential. These findings are important in understanding host plant suitability and evaluating the magnitude of injury to the crops attacked by BAW. Understanding such patterns of host utilization will be important to development of tactics involving manipulation of wild and cultivated hosts for incorporation into areawide management strategies.
Technical Abstract: Consumption rates, development times, and life table parameters of the beet armyworm [Spodoptera exigua (Hubner) (Lepidoptera: Noctuidae)] were determined on five host plants: cabbage (Brassica oleracea L.), cotton (Gossypium hirsutum L.), bell pepper (Capsicum frutescens L.), pigweed (Amaranthus retroflexus L.), and sunflower (Helianthus annuus L). Mean total leaf weight consumed by larvae was highest in cabbage (2.7 g) and lowest in pigweed (1.6 g). The feeding index (pupal weight divided by total weight of leaf tissue consumed) was highest on pigweed, followed by cotton, pepper, sunflower, and cabbage. On all host plants, significant relationships were found between amount of leaf tissue consumed and resulting pupal weight. Likewise, significant relationships were found between pupal weight and subsequent adult fecundity on all host plants. The highest percentage of female progeny was recorded in Spodoptera exigua reared on pigweed (62.2%) and the lowest for moths reared on cabbage (43.6%). Duration of the larval stage was shortest on pigweed (12.4 d) and longest on pepper (18.0 d). Larval survival was highest on pigweed (94.4%) and lowest on cabbage (67.1%). Three key statistics were used to assess performance of Spodoptera exigua on the different host plants: 1) feeding index; 2) intrinsic rate of increase, "r"; and, 3) growth index (percentage immature survival divided by immature development time). Using these measures, Spodoptera exigua performance was best on pigweed, worst on cabbage, and intermediate on cotton, pepper, and sunflower. We discussed the implications of these findings for control of Spodoptera exigua.