The toxic effect of α-tomatine on the 28-spotted potato ladybeetle Henosepilachna vigintioctomaculata (Coleoptera: Coccinellidae)

Abstract

Glycoalcoloids of plant origin serve as teratogens, causing various teratoses and abnormalities of insect development. Our previous studies discovered dependence of developmental defects in the 28-spotted potato ladybeetle Henosepilachna vigintioctomaculata upon its feeding on certain potato varieties. The present study was undertaken to study the toxic effect of α-tomatine against the 28-spotted potato ladybeetle. Tomatine was chosen as a model glycoalkaloid. Potato leaves were treated with tomatine solutions in different concentrations. Control leaves were treated with distilled water. Ten first-instar larvae were placed in a Petri dish with treated leaves. The effect of tomatine on H. vigintioctomaculata was assessed by appearance of morphological abnormalities in the adults. As a result, a confident direct correlation between the tomatine concentration and the developmental defect frequency was found. Brachelytry and cystelytry were the main anomaly types. When the stock 6 % solution was used, insect mortality was the highest, reaching 70 %. The highest level of teratoses (60 %) among survived insects and relatively high mortality (27 %) were observed in insects treated with 0.6 % solutions of tomatine. As the tomatine concentration decreased, so did the mortality level and developmental defect frequency. At 0.06 % solution treatement, mortality was 17 % and quote of teratoses – 47 %, at 0.006 % – 16.6 % and 6.8 %; at 0.0006 % – 3.3 % and 3.4 %, respectively. Thus, tomatine can be used as an insecticidal compound for potato cultivation.