Toxicity, Persistence, and Potency of Sabadilla Alkaloid Formulations to Citrus Thrips (Thysanoptera: Thripidae)

Abstract

Toxicity of the major alkaloids present in commercial formulations of sabadilla, Veratran D, was determined in laboratory bioassays with adult female citrus thrips, Scirtothrips citri (Moulton). Both cevadine and veratridine, the 2 major components of the insecticidal fraction of sabadilla, were highly toxic to citrus thrips. LC50S of cevadine and veratridine were 18.25 and 29.91 ng/cm2, respectively, whereas veracevine, the parent alkanolamine, was much less toxic (LC50 of 17,314 ng/cm2). A field trial with Veratran D showed that alkaloid levels on leaves declined to 60% of the initial deposit within 20 h of application and to undetectable levels within 7 d. Analyses of stored commercial samples of Veratran D from each year 1990-1994 indicated that levels 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 Veratran D taken in 1995 despite similar levels of total alkaloids among samples. Future formulations of Veratran D might be improved by standardizing the levels of cevadine and veratridine rather than the level of total alkaloids.