Repellent and Attractant Activity of Syngonium Podophyllum Schott (Araceae) Plant Extracts Against Three Stored-product Pests: Species-specific Responses of Tribolium Castaneum , Callosobruchus Chinensis , and Sitophilus Oryzae

Insects that live in stored grain and pulses are usually controlled with chemicals, but plant extracts that keep insects away, known as repellents, are a possible alternative. Most studies of plant repellents test only one kind of insect and ask only whether it is driven away. We asked whether the same plant extract could push one pest away while drawing another one in. Extracts of the ornamental plant Syngonium podophyllum Schott (Araceae) were prepared with three solvents, petroleum ether, chloroform and methanol, and offered to three major stored-product pests: the red flour beetle Tribolium castaneum (Herbst), the pulse beetle Callosobruchus chinensis (L.) and the rice weevil Sitophilus oryzae (L.). In each test dish, one half was treated with extract and the other half was left untreated; ten adult insects were released in the centre and counted on each side every hour for five hours, at five doses with three dishes per dose. The red flour beetle and the pulse beetle avoided all three extracts, and did so in every one of the 90 dishes in which they were tested; average repellency was about 55% for petroleum ether, 44 to 51% for chloroform and 22 to 25% for methanol. The rice weevil behaved differently: it was repelled only weakly and inconsistently by petroleum ether, was not affected by methanol, and was attracted to the chloroform extract, settling on the treated side in all 15 of its dishes. The chloroform extract, which killed none of the three pests in toxicity tests, was therefore one of the most active materials in changing their behaviour. These results show that one plant extract can have opposite effects on pests that share the same store. A treatment that protects pulses or flour could draw rice weevils toward stored cereals, while the attractive fraction could be developed as a bait for weevil traps.