Time- and Dose-dependent Toxicity of Syngonium podophyllum Schott (Araceae) Plant Extracts to Three Major Stored-product Pests

Insects that attack stored grain and pulses cause large losses of food, and the chemicals used against them are becoming less effective as the insects develop resistance. Plant extracts are one possible alternative. We tested extracts of Syngonium podophyllum Schott (Araceae), an ornamental plant grown widely in gardens and homes, against three of the most damaging stored-product pests: the red flour beetle Tribolium castaneum (Herbst), the pulse beetle Callosobruchus chinensis (L.) and the rice weevil Sitophilus oryzae (L.). Dried plant material was extracted in turn with three solvents, petroleum ether, chloroform and methanol, which draw out different groups of plant chemicals. Adult insects were exposed to four doses of each extract, in three dishes of ten insects per dose, and dead insects were counted every 6 hours for 48 hours. The petroleum ether and methanol extracts killed all three pests, whereas the chloroform extract killed none. The petroleum ether extract was the most toxic: after 24 hours, the dose needed to kill half of the insects was 0.22 mg cm −2 for the red flour beetle and about 0.64 mg cm −2 for the other two pests, and it was two to six times more potent than the methanol extract. Mortality kept rising with time in every case, so less extract was needed the longer the insects were exposed, and at the highest petroleum ether doses half of the insects died within about 6 to 11 hours. These results show that S. podophyllum contains compounds that are toxic to major storage pests, mainly in its non-polar fraction. Identifying these compounds, and testing them on stored grain under practical conditions, are the next steps.