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Feeding Activity, Growth, and Survival of Soybean Looper on Low-Nitrogen Nonnodulating Soybean

Dep. of Entomology, Louisiana Agric. Exp. Stn., Louisiana State Univ. Agric. Ctr., 402 Life Sciences Bldg., Baton Rouge, LA 70803-1710

^* Corresponding author.

Feeding and larval development of several lepidopteran species are influenced by reduced foliage N of host plants. Nonnodulating soybean [Glycine max (L.) Merr.] isolines have exhibited foliar symptoms typical of N deficiency in field plots in absence of supplemental N. Under these chiorotic conditions, reducedefoliation and larval development of soybean looper [Lepidoptera:Noctuidae, Pseudoplusia includens (Walker)] have been observed. This study was conducted to evaluate the influence of foliage N level of nodulating and nonnodulating soybean isolines on feeding and development of the soybean looper. Two feeding studies involving the soybean looper and foliage of nodulating and nonnodulating isolines of *#x2018;Clark’ soybean were conducted using foliage collected from plants in full bloom (R2) and in the beginning seed stage (R5). foliage N level of the nonnodulating isoline was not significantly lower than that of the nodulating isoline when collected at R2 and, consequently, only slight effects on feeding and development were attributable to consumption of nonnodulating isoline foliage. However, chlorosis and a 43% reduction in the foliage N level of the nonnodulating isoline occurred by R5, resulting in limited compensatory feeding, extended larval development, and reduced survival when soybean loopers consumed this isoline. Foliage N concentrations of 40 mg g^–l leaf dry weight were suiticient for soybean looper development from the neonate to the adult stage, while concentrations of 23 mg g^–1 leaf dry weight were inhibitory.

Received for publication September 27, 1993.