Notes on the Sweet Potato Pyralid Moth, Megastes grandalis, Guen.
AbstractMegastes grandalis, Guen., is distributed throughout Trinidad, and during certain seasons is a very serious pest of sweet potatoes (Ipomoea batatas), the only food-plant known at present. The early stages are described.
The larvae tunnel through the underground parts of the plant, leaving only the cortex untouched; there is consequent stunting of growth, shedding of leaves, and lack of tuber production. If tubers are formed, they are often riddled by the larvae, which penetrate to them through the roots. The eggs are firmly fixed in the axils of the leaf-petioles or on either side of the basal veins on the lower surface of the leaf. They may be laid singly or several in a row, but never in clusters. In captivity the number laid by one female varied from 130 to 180 over a period of 2-3 days. In March and April they hatch in a week. The larva begins feeding at once near the spot where the egg was laid. In the field it soon travels to a position just above the surface of the ground, where it finally enters the stem and bores down the root. The larval stage lasts 5-7 weeks. The cocoon is spun near the opening above ground, from which the moths emerge 17-21 days later, the actual pupal stage lasting 13-16 days.
Trichogramma minutum, Riley, was reared from the eggs, and Sarcophaga sternodonta, Towns., from the full-grown larvae. Another Tachinid, Masicera? abdominalis, Wulp, and according to Urich, the Ichneumonid, Xyphosoma azteca, Cress., are also parasites of M. grandalis.