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Plantwise Technical Factsheet

coconut bug (Pseudotheraptus wayi)

Host plants / species affected
Anacardium occidentale (cashew nut)
Averrhoa carambola (carambola)
Carya illinoinensis (pecan)
Cinnamomum verum (cinnamon)
Cocos nucifera (coconut)
Eriobotrya japonica (loquat)
Litchi chinensis (lichi)
Macadamia
Macadamia integrifolia (macadamia nut)
Mangifera indica (mango)
Persea americana (avocado)
Psidium guajava (guava)
Theobroma cacao (cocoa)
List of symptoms/signs
Fruit  -  abnormal shape
Fruit  -  gummosis
Fruit  -  lesions: black or brown
Fruit  -  lesions: scab or pitting
Fruit  -  premature drop
Growing point  -  external feeding
Growing point  -  lesions
Inflorescence  -  external feeding
Inflorescence  -  fall or shedding
Symptoms
P. wayi is responsible for early nut-fall and gummosis of coconuts in East Africa. Young nymphs feed in the developing spadix at the base of the male flowers, or in the main stem and young branches which are still succulent. Older nymphs and adults tend to feed more on the developing nuts and female flowers. The toxic saliva of the bugs causes necrotic spots to appear. Young nuts are frequently killed by the toxic saliva (Hill, 1975).

In macadamia the feeding of P. wayi nymphs and adults can cause significant drop of flowers and young fruit. The kernels of premature fruit that do not drop after feeding by the bug are harvested with large necrotic lesions that badly deform the kernels. Feeding on more mature nuts causes less prominent lesions on kernels at harvest. Feeding activities can also cause large holes in the woody shell (ca 5 mm in diameter) and large brown, sticky lesions (ca 10 mm in diameter) on the inner surface of the husk. A characteristic of the feeding of P. wayi is the forming of gum on the outer surface of the fruit where the rostrum penetrated the husk. This can be seen at all fruit development stages (Bruwer, 1992).

Several researchers have described the damage and the occurrence of P. wayi in avocado orchards (De Villiers and Van den Berg, 1987; De Villiers, 1990; Du Toit and De Villiers, 1990; Dennill and Erasmus, 1991; Erichsen and Schoeman, 1992; Joubert, 1993; Joubert and Claassens, 1994). About 2 days after feeding on a mature avocado, the lesion can be recognised as a patch that is slightly darker than the rest of the skin and resembles a bruise. As the lesion becomes older it enlarges to approximately 8 mm in diameter, becomes indented like a hail mark and turns brown to black. The lesion may sometimes also become tumescent and wart-like. If the insect feeds on a young fruitlet, the avocado could become malformed and asymmetrical in appearance at maturity. Internally, the lesions display a brown stain that can penetrate the avocado fruit to a depth of 10 mm. It forms a typical hard clot that is easily removed together with the skin when the latter is pulled off. Coconut bugs do not cause rotting of the fruit flesh.

P. wayi was first recorded on guavas during 1977 (De Villiers and Wolmarans, 1980b) and has since become a pest of economic importance on this crop in South Africa (Van der Meulen, 1992). Nymphs and adults cause damage and the affected fruit can be recognized by the presence of pock-like lesions on the surface or dents in the skin of mature fruit so that the guava appears deformed. The insect also feeds on ripe fruit causing a soft circular lesion with a spot in the middle where feeding took place (De Villiers, 1992). Fruit rotting does not occur and most fruit are still edible and acceptable for the production of juice or pulp, but are less attractive for the fresh market. The lesions caused by P. wayi are often confused with hail damage (Van der Meulen, 1992).

Nymphs and adults cause damage to mangoes and both young and mature fruit are attacked causing fruit drop or lesions on the mangoes. A soft, watery spot on one or more parts of the fruit surface can help to distinguish affected fruit. This spot later darkens and dents occur in the peel. Damaged fruit usually drop when the normal fruit drop of mangoes takes place in October/November and therefore the damage caused by P. wayi is usually underestimated. If a damaged fruit does not drop, a clear indented lesion develops on the skin, often near the fruit stem. Internally the lesion is brownish and can be up to 10 mm deep in the fruit flesh (De Villiers, 1994).

The destructive capability of P. wayi in pecan orchards in Mpumalanga province, South Africa, is well known and contributes significantly towards kernel damage (Joubert and Neethling, 1995). Nymphs and adults can cause damage and many nuts are attacked in the early water stage of development, before the shells harden. Within a few days, distinct dark brown to black indented lesions become visible on the external husk surface and this often results in premature dropping. If nuts are injured at a later stage, for example, during or after shell hardening, similar lesions develop on the husk, while prominent dark brown to black kernel lesions can be observed when the nuts are shelled. These lesions render most of the kernels valueless (Joubert and Neethling, 1994).
Prevention and control

Biological Control

Oecophylla longinoda (Way, 1951), Anastatus sp. and Trissolcus sp. (Bruwer, 1992) are natural enemies of P. wayi.

Chemical Control

Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:


Impact
P. wayi is a serious pest in Kenya, Tanzania, and Zanzibar on coconut, but actual crop loss is difficult to assess, partly because of the natural nut-fall. Over 70% of young nuts will fall naturally and so many of the bug-damaged nuts would fall anyway. In certain areas of Zanzibar, crop losses of up to 100% can occur (Way, 1951).

A packhouse survey of insect damage to avocados in the Nelspruit/Hazyview area of South Africa indicated that damage by P. wayi during the 1990 season amounted to 4.7% (Dennill and Erasmus, 1991), wheras a similar study by Erichsen and Schoeman (1992) reported a figure of 2.8%. If these figures are representative of the annual crop loss, the avocado industry loses 2-4 million South African Rand per annum to P. wayi.

Van der Meulen (1992) concluded that the percentage damage caused by the coconut bug on unsprayed guavas in the Nelspruit area, South Africa, could range between 12.2% and 52.4% at harvest.
Related treatment support
Plantwise Factsheets for Farmers
Kenya, Kengap Horticulture Ltd; CABI, 2012, English language
 
 
External factsheets
Plant Health Australia Factsheets, Plant Health Australia, English language
PlantVillage disease guide, PlantVillage, English language
PlantVillage disease guide, PlantVillage, English language
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