Abstract
Four plant allelochemicals, gossypol, nicotine, tomatine and solanine, were tested for their effect on the host-parasitoid system of Heliothis virescens-Campoletis sonorensis. In this study, the common effects seen with nicotine, tomatine and solanine on H. virescens were reduced larval and pupal weights, prolonged time to pupation, but less growth reduction in parasitized than in unparasitized larvae. Gossypol at certain concentrations showed a positive growth effect on the parasitoid. This may have been mediated through its hormetic growth effect on the host. There were certain doses of gossypol that precluded adult emergence of H. virescens, but allowed parasitoid adult emergence. All four allelochemicals significantly prolonged the intra-host parasitoid development time. Concentrations at which these effects were observed and degree of the effect were different for each chemical. While effects common to all four allelochemicals were observed, some specific effects were also encountered. Nicotine was more toxic to parasitized than to unparasitized H. virescens larvae, while tomatine and solanine were equally toxic to both groups, based on LD50 (lethal dose that kills 50% of the population compared to control). Also nicotine caused the failure of parasitoid larvae to egress from host and form cocoons. In contrast, solanine did not disrupt egression or cocooning, but reduced adult emergence due to disruption of development inside the cocoons. Adult parasitoid weight was reduced by certain concentrations of gossypol and tomatine, while the other two chemicals did not affect adult weight. From the study of host-parasitoid biology, it was found that H. virescens exhibited developmental polymorphism, with two distinct groups of larvae having 5 and 6 instars each respectively. Significant positive relationships were found between host initial weight versus adult parasitoid weight, host initial weight versus maximum weight of the parasitized host, host instar versus adult parasitoid weight and weight of parasitoid female versus fecundity.
Gunasena, Galpathege Harshani (1988). Multi-trophic level interactions involving some plant allelochemicals, the herbivore, Heliothis virescens and the endoparasitoid, Campoletis sonorensis. Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -774023.