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Plantwise Technical Factsheet

coconut leafminer (Promecotheca cumingii)

Host plants / species affected
Areca catechu (betelnut palm)
Cocos nucifera (coconut)
Elaeis guineensis (African oil palm)
Metroxylon
List of symptoms/signs
Leaves  -  abnormal colours
Leaves  -  internal feeding
Leaves  -  necrotic areas
Leaves  -  necrotic areas
Symptoms
Damage caused by P. cumingii is of two types: adult feeding and larval feeding. Adult damage was seen to be heavier on the central, less mature leaves of the crown and larval damage on more mature lower whorls of leaves. Adult feeding marks are very characteristic and can be seen as longitudinal grooves of streaks on the lower surface of infested leaves. These grooves are demarcated by two adjacent veins running parallel to the midrib of each leaflet. These streaks are about 1 mm wide and up to 5 cm long, about two-thirds of them being only 1 cm long. Adult feeding in the initial stages was observed to be heavier towards the distal ends of both the leaves and leaflets, but subsequent feeding presents a uniform distribution of feeding streaks. However, during heavy adult feeding, the leaf tissue in the distal areas dries up more quickly than that in the thicker basal areas, thus causing dried up leaflet ends and leaf ends (Dharmadhikari et al., 1977).

Damage due to larval feeding can be easily distinguished as it appears in the form of blister mines. When the epidermal layers of the larval mine dry up a brown patch demarcating three areas of the mine is rendered non-functional (see Biology and Ecology). The damage by P. cumingii gives an impression of damage caused by fire or scorch resulting from sea spray to the casual observer's eye, rather than that of a pest attack.
Prevention and control

Field Monitoring

Field infestations of P. cumingii are mainly detected by surveying coconut plantations for signs of damage caused by larvae and adults. In Sri Lanka, 5-10 palms out of 50 palms are randomly selected to survey the pest population. One frond from a lower whorl is cut to take samples of leaflets.

Cultural Control

Perera (1975-1980) reported that if the pest is detected when only a few mines are present, the pest could be controlled to a certain extent by selectively cutting and burning the infested fronds. (However, this should be followed with parasitoid releases.) In the Philippines, it was recommended that ten old leaves should be cut off from each affected palm. Though a drastic treatment, this was considered to be no more severe than the damage caused by P. cumingii (Aldababa et al., 1931).

Biological Control

Fernando (1972a, b) reviewed the biological control programme of P. cumingii in Sri Lanka. De Souza (1972) provided details of the shipments of parasitoids from Fiji and Singapore to Sri Lanka. Several consignments of both Sympiesis javanicus and Achrysocharis promecothecae were received from Singapore in 1971. P. parvulus and P. painei were also introduced from Fiji, Singapore and Sabah (Malaysia). Laboratory rearing of these two species was difficult due to the presence of a hyperparasite, P. detrimentosus. Between December 1971 and October 1972, a total of 130 525 S. javanicus, 33 250 P. parvulus and 1250 A. promecothecae were released in the infested areas. S. javanicus established and multiplied rapidly and gave spectacular control of the pest. This control was also aided by local mortality factors such as diseases in eggs and larvae of P. cumingii (Fernando, 1972a, b).

Dharmadhikari et al. (1971) reviewed the P. cumingii parasitoid guild in Sri Lanka. He reported that no parasitoids of any value were present locally. But he noted that A. promecothecae was present initially at the infested sites, and diminished gradually to disappear altogether with the disappearance of the pest. This fact has left scientists in doubt as to whether Achrysocharis was indigenous or was imported accidentally.

Even though S. javanicus established rapidly in infested areas just after its introduction to Sri Lanka, presently it is P. parvulus that plays a very active role, controlling the pest at hot spots or sudden resurgences of the pest. This spectacular control of P. cumingii has been listed among 66 highly successful classical biological controls worldwide (Fernando, 1972a, b).

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
In the Philippines, Aldababa et al. (1931) recorded a maximum of 85% loss of coconut production due to P. cumingii approximately 1 year after infestation. Coconut yields are affected mainly due to the destruction of leaf tissues by the larvae and adults resulting in reduced photosynthetic activity. Infestations of P. cumingii were heavier on tall and older bearing palms compared to short and younger palms. It was observed that mild infestations prevailing over a long period do not appear to affect the crop directly; but in the long run the crop might be affected through gradual deterioration of the general health of the palm (Perera, 1975-1980). Kanagaratnam (1985) reported that P. cumingii has been a serious but localized pest of coconut in Sri Lanka ever since its accidental introduction in 1970.

Dharmadhikari et al. (1977) summarized a cost/benefit analysis of the P. cumingii control programme in Sri Lanka and estimated that the monetary value of the loss due to this pest in Sri Lanka was (Sri Lankan) Rs3 000 000.

P. cumingii was declared a serious pest of coconut under the Plant Protection Ordinance in Sri Lanka in 1971. The Philippine government did so in 1930.
Related treatment support
 
External factsheets
Pestnet Factsheets, Pestnet, English language
Solomon Islands Ministry of Agriculture and Livestock Farmer Fact Sheets, Solomon Islands Ministry of Agriculture and Livestock, 2012, English language
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