New Sweet Potato Pest

Examination Of An Infected Plant Sample At An Event Held To Celebrate World Food Day 2017.

A possibly new sweet potato pest was observed twice late last year in the parish of St. Philip. It was feeding on the foliage of  parish of St. Philip. It was feeding on the foliage of sweet potato, spinach and increase peas. The insect appears to be Agroiconota propinqua (Boheman), a small beetle of the Cassidinae (Tortoise beetles) subfamily of the Chrysomelid leaf beetles.

Egg: Oval and flattened and about 1 mm in length. They are attached singly to the underside of the plant leaf or stem and deposit in cluster of about 20 eggs. Female beetles lay from

50-90 eggs over a two-week period, which hatch in 5-10 days depending on the species and the environmental conditions. 

Larva: Broad and flattened with spines, some of which are branched. Most are yellowish to green in colour and pass through three instars (moult). Larvae feed on leaves, creating numerous holes in them.

Pupa: Brownish with spines and is attached to the leaf. The pupa is 5-8 mm in length and the pupal period lasts from 7 -14 days.

This the resting stage of the insects and it is from this stage that the adult beetle will emerge.

Adult: Shiny black with golden stripes (5-7 mm long). Adults also feed on the host plant leaves. The total life cycle ranges from 4-7 weeks. 

Biological Control

Worldwide, ten families of tiny wasps and three subfamilies of Tachinid flies parasitize the eggs, larvae and pupae of the Cassidinid beetles. In addition, predators such as ladybird beetles (Coccinellidae), ground beetles (Carabidae), damsel bugs (Nabidae), shield or stink bugs (Pentatomidae), assassin bugs (Reduviidae), green lacewings (Chrysopidae), and

ants (Formicidae) feed on the eggs, larvae and pupae of the Cassidinid beetles. These natural enemies can be utilised to control the infestation of the Cassidinid beetles and reduce the need for pesticides. 

Chemical Control

Systemic insecticides such as Actara® (thiamethoxam) and Rogor 40® (dimethoate) can be used to control the larvae and adults of A. propinqua. However, if you prefer to use an organic insecticide which is less harmful to the beetle’s natural enemies, a neem formulation such as Neem-X® (azadirachtin) can be applied. These insecticides should always be applied only at the recommended rate. Always wear protective clothing when applying pesticides.