Mungbean Insect Pests
 

Bean Pod Borer
Maruca testulalis 

Found throughout Asia

Where to look

Inspect the flowers and the developing mungbean pods. If the pods look malformed or you see entry holes on the surface, cut them open. Look for feeding damage, frass, other insect debris, and the borer itself. The larva is often found among the external webbing of pods and leaves. If two or more pods or leaves and pods are touching, a borer is often found at the juncture or inside the pod.


Technical information

Eggs are laid on the sepals or petals of the flower. The larva feeds for about 3 weeks. At night, it emerges from the pods and crawls about. It then descends to the soil and pupates beneath leaf debris. Cowpea is also a common host of this pest.


Control

Because of the hidden nature of larval stage (the damaging stage) and pupal stage, it is difficult to control Maruca podborer by chemicals or other conventional means. Insecticides have been widely used in Asia, especially on yardlong bean where fresh pods are marketed as vegetables in SE Asia. However, there is only a brief period from hatching to entering buds or pods, thereby requiring farmers to apply chemicals frequently. This is not always economical or suitable for human health.

In field crops of mungbean and cowpea, insecticide use is much less due to the relatively short flowering period compared to yardlong bean. In most countries hardly any chemical is recommended specifically for Maruca on mungbean.

For Maruca on cowpea, several commonly used insecticides such as endosulfan, carbaryl, methomyl, monocrotophos have been found effective. The first application should be made at least one week before flowering and continued at a weekly interval until three weeks after peak flowering.