TOXICITY, PERSISTENCE, AND POTENCY OF SABADILLA ALKALOID FORMULATIONSTO CITRUS THRIPS (THYSANOPTERA, THRIPIDAE)

Toxicity of the major alkaloids present in commercial formulations of sabadilla, Veratran D, was determined in laboratory bioassays with adu lt female citrus thrips, Scirtothrips citri (Moulton). Both cevadine a nd veratridine, the 2 major components of the insecticidal fraction of sabadilla, were highly toxic to citrus thrips. LC(50)s of cevadine an d veratridine were 18.25 and 29.91 ng/cm(2), respectively, whereas ver acevine, the parent alkanolamine, was much less toxic (LC50 of 17,314 ng/cm(2)). A field trial with Veratran D showed that alkaloid levels o n leaves declined to 60% of the initial deposit within 20 h of applica tion and to undetectable levels within 7 d. Analyses of stored commerc ial samples of Veratran D from each year 1990-1994 indicated that leve ls of each of the 2 major alkaloids, as well as the ''total'' alkaloid content determined gravimetrically were similar. In contrast, >3-fold variation in the level of veratridine was noted in 4 samples of Verat ran D taken in 1995 despite similar levels of total alkaloids among sa mples. Future formulations of Veratran D might be improved by standard izing the levels of cevadine and veratridine rather than the lever of total alkaloids.