Effect of constitutive and herbivore-induced extractables from susceptible and resistant soybean foliage on nonpest and pest noctuid caterpillars
Wheeler, G.S. | Slansky, F. Jr
Soybean foliage from susceptible ('Bragg') and resistant (PI 229358 and D75-10169) lines was extracted in several nonpolar and polar organic solvents to assess constitutive (mite-free) and induced (mite-damaged) activity against nonpest and pest noctuid caterpillars. The benzene fraction, incorporated in artificial diet, contained most of the constitutive activity of both the resistant and susceptible lines, as indicated by reduced relative growth rate (RGR) of velvetbean caterpillar, Anticarsia gemmatalis Hubner; corn earworm, Helicoverpa (= Heliothis) zea (Boddie); tobacco budworm, H. virescens (F.); and fall armyworm, Spodoptera frugiperda (J. E. Smith) compared with larvae fed the extract- and solvent-free control diet. Induced activity from mite-damaged greenhouse-grown plants and A. gemmatalis-damaged field-grown plants was detected primarily in the petroleum ether fraction. Among the species tested on the induced fractions (A. gemmatalis, S. frugiperda, and the cabbage looper, Trichoplusia ni (Hubner)), S. frugiperda was the most sensitive species, as demonstrated by reduced RGR. Overall, among the species (H. zea, H. virescens, and T. ni) more tolerant of the soybean foliage fractions, only H. zea is a major soybean foliage pest. Surprisingly, among the two most sensitive species, A. gemmatalis is a legume specialist and major soybean pest, whereas S. frugiperda is a polyphagous species but not a soybean pest. These results suggest that presumed soybean-adapted species may not be more resistant than soybean-naive species to the deleterious effects of soybean foliage extracts.
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