Figs are one of the most rewarding fruit trees to grow in the garden, their fleshy sweet fruit one of summer's favourite delights. As much as we enjoy the rewards of growing a fig tree, there are a few critters and pests to keep your eyes on, especially during the warmer months. One of these pests includes the devouring Fig tree borer.
The fig tree borer is indigenous and occurs in most parts of Africa and has become abundant in the Western Cape during the 1990s.
The female lays eggs in slits in the bark of stems, especially the main trunk. Larvae are cream-coloured and legless grubs with well developed strong mandibles. Mature larvae can reach a length of up to 4 cm. The pupae are found beneath the bark surface enclosed in cells formed by calcium carbonate combined with silk and gum. Adult beetles are strong, robust, typical longhorn beetles with a body length of 3,5 cm. Beetles are dark, greyish-brown in colour with a prominent spine on both sides of the thorax. Male beetles are smaller than females.
The adult fig tree borer beetle. A typical longhorn beetle which belongs to the Cerambycidae family.
The original host plant of this borer beetle is the Cape willow, Salix mucronata, from which it has adapted to attack the domestic fig, Ficus carica. Potentially they will also attack wild figs, the exotic weeping willow (Salix babylonica), pear and peach. Adults can also feed on the bark of a variety of trees, such as Syringa (Melia azedarach), apple, nectarine, plum, apricot and grapevine.
Adults can cause external damage by nibbling on the bark and can cause some crop loss by feeding on the skin of unripe figs. However, the most significant damage is caused internally by the larvae. Their tunnels in the tree weaken the trunk and a severe infestation can cause the host tree to die, or the tree can break in strong winds. Furthermore, young trees can die if they are ring-barked by adults.
Different stages of larvae of the fig tree borer. The dark mandibles are visible in all sizes.
This beetle has become a serious pest, especially in gardens where preventative measures are usually not in place.
After mating, the female can lay up to four eggs at a time in a T-shaped slot in the bark. This usually takes place in the lower parts of the trunk, but can also occur on branches. Oviposition (egg-laying) starts usually around November and can last until March. Each female can lay up to 35 eggs in their lives.
Larvae emerge roughly two weeks after oviposition. The young larvae will start feeding on the bark, chewing into the wood, creating tunnels inside the trunk or branch. The wood is not very nutritious and therefore it can take 2.5 – 3 years for the larvae to mature before they start to pupate. During pupation, it pushes out a mixture of excrement (frass) and sawdust through holes of the bark. This phenomenon is a clear sign of an infestation. The pupal stage lasts about three months after the adult beetles emerge.
The larva can be seen inside the tree. The bark is swollen where the tunnel is.
Controlling the fig tree borer
There are currently no known natural enemies of this borer. Control can be difficult as beetles are seldom seen on trees as they are able to fly and, for most of the time, the larvae are inaccessible to pesticides.
The best control is to prevent the female from laying eggs in the trunk. Do this by wrapping a protective barrier around the trunk of the fig tree, usually the first 400mm from the base of where the roots start. Materials often used include gauze mesh covered by fine stell.
Branches can also be sprayed with a synthetic pyrethroid to kill larvae as they emerge, but this method should be carried out a number of times to give protection throughout the season. Insecticides can also be injected into the tunnels if the larvae cannot be found. You can cut the larvae out with a sharp knife and kill them. Use Tree-seal to protect the infested hole from secondary infections.
Damage done by the fig borer beetle.