Entomologia Experimentalis et Applicata 99: 71–77, 2001. © 2001 Kluwer Academic Publishers. Printed in the Netherlands. 71 Antimetabolic effects of plant lectins towards nymphal stages of the planthoppers Tarophagous proserpina and Nilaparvata lugens K. S. Powell University of Technology, Department of Agriculture, PMB Service, Lae, Papua New Guinea Present address: Agriculture Victoria, RMB 1145, Rutherglen, VIC 3685, Australia (E-mail:kevin.powell@nre.vic.gov.au) Accepted: November 7, 2000 Key words: Tarophagous proserpina, Nilaparvata lugens, Galanthus nivalis agglutinin, Con A, Psophocarpus tetragonolobus agglutinin, insect bioassay, artificial diet, Homoptera, Delphacidae Abstract Taro Colocasia esculenta (L. Schott) and rice (Oryza sativa L.) form a major part of the staple diet of pacific islanders. Pest constraints hamper the sustainability of taro and rice production in the Pacific region. Insect feeding trials were conducted in vitro to determine the effects of plant lectins against planthopper pests of taro and rice. Lectins were incorporated into artificial diet at 0.1% (w/v) level. The lectins Galanthus nivalis agglutinin (GNA) and concanavalin A (Con A) showed significant antimetabolic effects towards third instar nymphs of taro plan- thopper (Tarophagous proserpina Kirkaldy) whilst Pisum sativum agglutinin (PSA) showed no significant effects toward the insect. Psophocarpus tetragonolobus agglutinin (PTA) showed significant antimetabolic effects towards third instar nymphs of rice brown planthopper (Nilaparvata lugens Stål). PTA also reduced honeydew excretion levels of rice brown planthopper, over a 24-hour period, demonstrating antifeedant properties of the protein. Introduction The insect family Delphacidae contains a large group of sap-sucking planthoppers affecting a wide range of economically important crops including taro and rice. Taro Colocasia esculenta (L. Schott), is a root crop which is grown throughout the tropics and sub-tropics. It forms part of the staple diet of many pacific islanders and is also grown commercially. In the South Pacific region taro is affected by the economically important insect pest, taro planthopper [Tarophagous proserpina Kirkaldy (TPH)]. In SE Asia and the Pacific Islands of Papua New Guinea and the Solomon islands one of the most economically important rice pests is the rice brown planthopper (Nilaparvata lugens Stål, BPH). Both BPH and TPH cause direct damage, including yellowing (hopperburn) and stunting, due to adult and nymphal feeding and oviposition damage to stems (Mitchell & Maddison, 1983). Both insects also act as vectors of economically important viruses. TPH acts as a vector for two rhabdovirus diseases, Alomae and Bobone, which are found exclusively in Papua New Guinea and the Solomon Islands (Rodoni et al., 1994) and can result in up to 100% and 25% yield loss respectively (Gollifer et al., 1978). Neighbouring islands are major exporters of taro and virus-carrying TPH are a significant quarantine risk to the region. The lack of suitable pest management strategies to control pests and diseases of both taro and rice has resulted in a decline in traditional taro farming prac- tices and successive failures to introduce wide-scale rice production in Papua New Guinea and the Solomon Islands. Genetic engineering, as part of an integrated pest management approach, could allow the development of a novel unique control option in the form of homopteran-resistant root and cereal crops in de- veloping countries, which rely on low-input sub- sistence agriculture. Lectins with a range of spe- cific carbohydrate-binding affinities have been iso- lated from a variety of plants and tissue sites and the toxic effects of these compounds towards insects,