Symposium: Insect Behavioral Ecology--'90: Nutritional Indices: Do They Explain Toxicity of Calliandra Amino Acids?

Christopher S. Shea, John T. Romeo

Abstract


Calliandra leaves and the nonprotein imino acids they contain possess insecticidal activity. In order to determine the role these compounds play in Calliandra resistance to herbivory, feeding experiments were performed using larvae of the polyphagous herbivore Spodoptera frugiperda Smith, and nutritional indices were calculated. Statistically significant growth inhibition occurred with the total amino acid fraction and trans-5-hydroxypipecolic acid, and there was a trend toward similar inhibition with several other imino acids. The efficiency with which larvae converted assimilated food into biomass (ECD) was reduced by the total amino acid fraction as well as by two imino compounds. The consumption index (CI) and the diet digestibility (AD) were unaffected by amino acids. Leaf material caused significant growth inhibition, increased mortality, and a dramatic decrease in the growth and survival of progeny. Leaf material lowered AD, raised relative consumption rates (RCR) and lowered the efficiency of conversion of the ingested food (ECI). The data suggest that nonprotein amino acids acting as toxins via negative effects on insect nutritional physiology are part of Calliandra resistance to herbivory.

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