Alleviation of α-tomatine-induced toxicity to the parasitoid,Hyposoter exiguae, by phytosterols in the diet of the host,Heliothis zea.

The solitary, endoparasitic ichneumonid,Hyposoter exiguae (Viereck) is a parasitoid of the tomato fruitworm,Heliothis zea (Boddie). However, the parasitoid is deleteriously affected by the tomato glycoalkaloid, α-tomatine, ingested from hosts (H. zea) fed on artificial diets or semipurified extracts of tomato plants that contained α-tomatine. α-Tomatine causes prolonged larval development; disruption or prevention of pupal eclosion; deformation of antennal, abdominal, and genital structures; and reduction in adult weight and longevity of the parasitoid. These toxic effects are exacerbated when the dietary dose of α-tomatine is increased from 12 μmol to 20 μmol/g dry wt of diet. However, the toxicity of α-tomatine is attenuated in parasitoids reared from hosts fed on artificial diets that contain equimolar or supramolar amounts of 3β-OH-sterols admixed with α-tomatine. Further, the toxicity of extracts from the foliage of different cultivars of tomatoes toH. exiguae is contingent upon the composite levels of α-tomatine and total phytosterol (free and esterified). Cultivars with a low total sterol-tomatine ratio are more toxic toH. exiguae. The possible mode of action of α-tomatine toxicity toH. exiguae by disruption of sterol metabolism is discussed.