Resistance to Insect Pests of Perennial Castors

Abstract

The relative resistance to insect pests of two Thai perennial type castorbean varieties (Lai Kao Dum and Thon Nuan) was studied in Ban Mai Samrong district of Nakorn Ratchasima district in Northeast Thailand during the period May 1987 – April 1988. The paired comparisons were made under carbaryl treated and untreated conditions. The Thon Nuan variety was relatively less susceptible to leafhopper (Jacobiasca formosana Paoli) infestation. In the treated plots an average of 226 leafhopper nymphs per 50 leaves was found in Lai Kao Dum, compared with 66 in Thon Nuan. In the untreated polts the counts were 1,337 and 227 for Lai Kao Dum and Thon Nuan, respectively. By the end of the season 73 percents of Lai Kao Dum and 27 percent ot Thon Nuan plants had died as a result of severe leafhopper infestation. Of the less significant insect pests, rose bettle (Hypomeces squamosus F.) was more common in Lai Kao Dum, while castor semilooper (Achaea janata L.) and red mite (Tentranychus truncates Ehara) were more prevelant in Thon Nuan. The yield of Thon Nuan under the carbaryl treated and untreated conditions was 1,247 and 588 kg/ha, respectively. For the variety Lai Kao Dum the respective yields were 520 and 48 kg/ha.