Lima bean podborer

Etiella zinckenella (Treitschke)

Lepidoptera: Pyralidae

The lima bean podborer is a comopolitan pest and present on all continents.

Host plants and damage

Lima bean podborer is a pest on legumes including Vigna ungiculata (cowpea), Cajanus cajan (pigeon pea), Phaseolus vulgaris (common beans) and Vigna radiata (mung bean).

Infestation occurs in legumes mainly during the fruiting stage and larvae feed on flowers, fruits, and seeds. They cover the pod with a small web and bore through the pod pericarp, feeding on developing seeds. More than one larva can enter a pod but cannibalism reduces the number of larvae per pod.

Blossoms drop as a result of larval feeding.

Morphology & biology

Eggs are laid singly or in small batches on young pods, calyxes or on leaves. Females lay up to 200 eggs. They are white but turn pink at the end of the incubation period. First instars hatch after 5-6 days at 30 °C.

Lima bean podborer have five larval stages: the first instar is 1 mm long with a yellowish body and a black head capsule, whereas the last instar can reach 15 mm in length. Larval development takes three weeks. Mature larvae bore into the soil and pupate in a cocoon.

Male pupae are generally larger than female. The pupal period lasts 8-12 days.

Moths live up to 20 days. They are brown-grey with a white stripe along the leading edge of the forewings. The wingspan measures 19-27 mm. Adults are morphologically similar to E. hobsoni and E. behrii. The species can be separated based on genital characters.

Monitoring

Adult lima bean podborer population can be monitored with light traps and/or sex-pheromone traps. The sex-pheromone blend, which attracts the European strain of E. zinckenella is ineffective in South-East Asia.

Holes in the pod pericarp indicates infestation. However, for correct identification pods have to be opened and larvae examined.

Pest management

There has been limited success in controlling the pest by means other than insecticides.

Biological control

It also has large number of parasites, despite its cryptic nature, which provide an opportunity for biological control of this pyralid. So fare none of the reported natural enemies control the Lima bean podborer effectively.

Chemical Control

Frequent sprays of insecticides can be used to kill first instar larvae before they enter the pods. The time frame for insecticide application is short because first instars enter the pod only a few hours after hatching. Soybean pods are covered by a leaf canopy, which makes it difficult to target larvae directly with insecticides.