The objective of this study was to determine whether the presence of a deleterious chemical in a preferred host plant could alter the feeding preference of a polyphagous insect. The preference of the Asian armyworm, Spodoptera litura (F.) (Lepidoptera: Noctuidae) for castor, Ricinus communis (L.) (family: Euphorbiaceae) relative to cabbage, Brassica oleracea (L.) (family: Brassicaceae) was quantified by two separate two-way choice tests (without treatment and with treatment of the test chemicals used in the present study) with naive third instar larvae each time. This was followed, by continuous feeding (48 h) on the preferred host treated with the test chemicals and using naive third instar larvae for conditioning. Each treatment consisted of one of nine compounds, including seven naturally occurring allelochemicals (viz. (-)-alpha-pinene, (-)-beta-pinene, beta-myrcene, D-limonene, cineole, rutin, and ajwain oil) and two synthetic insecticides (viz. alphamethrin and malathion). Following this, a two-way choice test was repeated with the same batch of larvae without any test chemical. Larvae continued to maintain preference for castor despite exposure to the deleterious chemicals. Among the test chemicals, D-limonene and alphamethrin caused significant reduction in growth. Preference for castor was not overcome by exposure to novel deleterious chemicals, suggesting that aversion, though experienced is not learned.

Foreign