1. Spiral borer: Agrilus acutus (Buprestidae : Coleoptera)
It is a serious pest of mesta. The insect bores through the main stem of the plant. It forms rings on the main stem and the stem breaks from that portion. The fibre obtained from the infected plants become useless.
The eggs are ovate and scale like, and are laid singly on the stem, usually near a leaf scar. Egg period 10 -12 days. The larva bores through the lower surface of the egg directly into the stem and feeds under the bark forming a sprial tunnel. There are normally three moults in the active feeding stages, but exceptionally four, and a prepupal moult. The larval stage lasts 26 days. The fully grown larva is 21 mm. long and bores into the wood to pupate, making a pupal chamber 11 mm. long into which it fits itself by adopting an asymmetrical U-shaped posture. After a prepupal stage of 2.5 days it pupates. The pupal period occupies about 11 days and a further seven days are spent by the adult in the pupal chamber. |
