The weevil, Sternochetus mangiferae (F), is a common pest an animal or plant causing damage to crops in Kenya and can be found in all local mango-growing areas. It is spread mainly by transportation of infested fruits since the weevil develops within the mango seed and can therefore be transported easily from one locality to another unnoticed. The mango weevil does not usually damage the fruit and consequently is not a serious pest as far as local consumption of the fruit is concerned. However, this pest hinders the development of a fresh fruit export market because the leading import countries in the Middle East and other places maintain strict quarantine the prevention of importation or exportation of unwanted organisms into a territory regulations.
Infestation symptoms are most obvious within the seed where the weevil largely completes its life cycle. Here all stages of the insect development—larvae, pupae and adults—can be found. Externally the affected fruits appear normal, but very often are rotting from inside.
The female usually lays her eggs over a period of 5–6 weeks on fruits before these are half-grown. The hatching period is 3–5 days. The young larvae penetrate the fruit and eat their way to the seed where they feed and develop into adult weevils. These emerge from the stone by tunnelling outwards through the flesh and skin of the fruit, leaving an unsightly patch where rotting soon sets in. Once the weevils have left the fruit they search for a hiding place such as beneath loose bark of trees or in waste material under the trees where they spend the time of the year that is unfavourable for them.
To date, chemical control untreated subjects used for comparison with those given a particular treatment measures against this pest have not proved economical. However, implementing the following three steps will definitely reduce the weevil population in the orchard.
The biggest source of infestation is dropped fruits or seeds lying around in which weevils can survive up to about 300 days. Therefore, regular removal and destruction of waste material up to the end of the harvesting period is very important and effective.
The most suitable stage for control is during the emergence and oviposition of the adult weevil. The first step to suppress the weevil population is implemented at the beginning of the mango flowering season by using preferably long-lasting contact insecticides such as Azinphos, Endosulfan, Malathion and Fenthion. It is important to thoroughly wet (by spraying) the bark of the trunk the main stem of a tree and scaffold branches or brush the insecticide chemical to control crop pests mixed with a suitable carrier material serving as diluent for the active ingredients on to the bark.
After fruit set, carry out spray treatments mainly focussed on single fruits using Carbosulfan, Malathion, Azinphos etc. mixed with a spreader/sticker material added to a spray to increase retention on plant foliage liquid. Repeat applications at intervals of 2–3 weeks and combine this with the control of anthracnose.
The mango is usually attacked by three to four key pests which require annual control measures. However, there are a number of occasional pests which may become troublesome only in localized areas or because of the occurrence of unusual circumstances. These pests include mites, thrips, scales, cecid fly and mealybugs.