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Insect Pests of Cashew

There are several insect pests attacking cashew in Tanzania. Five most important insect pests include:

Helopeltis bugs (Helopeltis spp)

Coconut bugs (Pseudotheraptus wayi)

Stem borers Mecocorynus loripes )

Mealy bug  (Pseudococcus longispinus )

Thrips (Selenothripis rubrocinctus Giard

Helopeltis bugs (Helopeltis spp)

Nymphs and adults attack young and tender leaves, shoots, flowers and fruits (nuts and apples). The saliva of the insects is very toxic and the site of attack is marked by lesions (brown to black in colour).  Severe attack of the shoot may cause dieback and heavily infested trees can be recognized from a distance by their scorched appearance.

Control Measures

African weaver ants (Oecophylla longinoda) have proved to be very effective as bioagents to Helopeltis and other  sucking bug control. The bugs seldom attack trees colonized by weaver ants. Weaver ants should thus be enhanced through nest transfers, rope bridges and control of antagonistic ants.

In the absence of bioagents, Karate (lamda cyhalothrin), a synthetic pyrethroid together with her generics, are very effective insecticides in the control process. Spraying should be repeated when new infestations become apparent.

Coconut bugs (Pseudotheraptus wayi)

Coconut bugs are generally reddish brown dorsal section with a greenish abdomen. Larvae and adults suck developing shoots and nuts. After attack young nuts shrivel, dry and blacken before they fall off. Feeding points becomes sunken spots and mature kernels will show black and sunken spots, which lowers their market value.

Control strategies

Similar control approaches used against  Helopeltis spp should be used for coconut bugs as well.

Stem borers  (Mecocorynus loripes )

Adult weevil is dark-gray in colour, about 18-26mm long. They lay eggs isolated in little excavations made by females in the bark of the trunk and large branches of a tree.

Larvae are typical weevil grabs which tunnels down beneath the bark, eating the sapwood of the tree causing substantial economic damage to the crop.  Heavily infested trees dies in a short period of time. Both larvae and pupa are causes `damage to the crop. Generally, the attack is limited to a few trees at a time, only when the tree is completely dead does the insect move to the next tree.

Control measures

Efficient control approach should mainly target larvae stage during early stages of infestation. However, the whole control approach is basically physical confrontation, whereby adults should be collected and destroyed. Also the bark around the infested area should be removed to expose the larvae, who when dropped down will never climb up the trunk again as they have no legs. The pupae can be destroyed by inserting a sharp article inside their chambers. No insecticide is so far recommended for stem borers.

Mealy bug  (Pseudococcus longispinus )

Adults are usually slow-moving insects and are called mealy bugs because most species secrete a thin cover of white mealy wax over the surface of the body.  They attack leaves, flowers or fruits sucking sap, often injecting toxic saliva and may spread virus diseases.

 

Control Measures

Bioagents such as Ladybird beetles (Chilocorus spp) and Lacewing flies (Chrysopa spp) have been found associated with mealy bugs, however their low population levels renders them inefficient as bioagents to control mealy bug. However, Selecron 720 EC (Profenofos ) is the only pesticide so far  recommended for mealy bug control on cashew.

Thrips (Selenothripis rubrocinctus Giard

Harmful forms: Nymphs and adults

Parts attacked:  Mature leaves and flowers (inflorescence).

The adults are dull dark brown body or black in colour with reddish strip on the first three abdominal segments, 1.3 1.8mm long. Lays eggs on lower leaf surface. At the tip of abdomen, curved upwards, amidst the anal setula, the larvae do carry a globule of a clear liquid, which is deposited on leaves. As it dries, this liquid gives rise to the formation of small brownish or blackish spots.

Both nymphs and adults suck and scrape underside of the leaves, mainly along the main veins, causing yellowing  that conglomerate and progressively turn gray, giving the leaves silver appearance, as a result may fall-down precociously. Heavily infested flowers may not open for fertilization, thus dramatically, lowering crop yields.

Control measures

Control should mainly target larvae stage during early stages of flowering. Karate (lamda cyhalothrin), a synthetic pyrethroid together with her generics products are very effective against thrips.  Spraying should be repeated when new infestations become apparent.

 

List of Other insect pests

Common name

Scientific name

Leaf miners

Acrocercops syngramma

Groundnut leaf hoppers

Hilda patruelis

Aphids

Aphis craccivora

Stem girdler

Paranaleptes reticulate

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