September 2017. Message about a stem borer problem in cocoa in the Ivory Coast. The member wrote that they had started an integrated cocoa pest management study with smallholders in Côte d’Ivoire. Many areas are particularly affected by stem borers. We observe symptoms in the field that suggest two different types: one that is penetrating the hardwood of stem and branches; and another one that channels the sapwood just below the bark (destroying the vital cambium layer) and also goes below the soil surface (attacking roots).
Attached are the stem borers found in a cocoa plantation. The first picture shows two larvae (the largest about almost 1 cm thick and 5 cm long) that were found dead below affected trees (after bored channels had been treated with acetamiprid and indoxacarb), whereas the second picture shows a larvae that was found in deteriorated superficial cocoa stem wood on the same plantation. This larvae on the second picture appears smaller and more slender.
I was wondering whether these are the same species? We have always assumed them to be Eulophonotus myrmeleon (a moth); but some have suggested cerambycid (longicorn) beetles such as Tragocephala spp. (which are also reported as a cocoa wood borer).
A member wrote about experiences in Cambodia and Vietnam where the legs of beetle grubs and moth larvae are a way to distinguish between them. The aim is to be able to distinguish between boring and soil dwelling insect pests of vegetable crops. Beetle larvae having a head capsule and true legs at the front of their body, but no ‘legs’ at the back, whereas lepidiopteran larvae normally have a head capsule plus true legs at the front, PLUS usually legs at the back (pro-legs). So, you can see you have here in these photos 2 types of larvae, beetle larvae and a caterpillar (lepidopteran larva).
Another suggestion was that the two grubs in the one image were cerembycids, with the characteristic body shape, lack of legs and small head capsule.