Coconut Leaf Beetle pg.2
Biology of the beetle:The adult coconut leaf beetle is 7.5 -10 mm long and 1.5 – 2 mm wide, with a flat body that is black in color and an orange head and shoulders. The adult male is generally smaller than the female. The larvae and adults are nocturnal in habit and remain in the unopened leaflets, moving outside only to infest nearby palms or for mating. The beetle is capable of only short flights – often only a few hundred meters – so its natural spread is slow. The eggs are brown and flat (1.4 mm long and 0.5 mm wide), commonly laid in longitudinal rows (surrounded by debris and excrement) in the unopened leaflets of both young and mature palms. They hatch in 3 – 7 days to form larvae that are white with two pincer-like spines at the rear end of the body. Older larvae have an average length of 8 – 10 mm. Larvae undergo four to six larval instars in a period of 30 – 50 days. The pupae are yellowish-white and measure 9 – 10 x 2 mm. The pupal period is four to six days. The whole cycle from egg to adult takes 5 – 9 weeks. The adult leaf beetle is fully mature two weeks after emergence from the pupa and lives for two to three months.
Symptoms of attack and damage: The beetle attacks palms of all ages, but young palms are more susceptible than older ones, because the heart leaves of old palms are firmer and less suitable as breeding grounds for the beetle. Larvae of the beetle chew on large areas of the surface of leaflets still in the throat of the palm (the spear leaf), which causes the death of underlying tissues. Such leaflets show longitudinal white streaks. As the leaf emerges, the leaflets curl and turn brown, giving a characteristic scorched and ragged appearance. Photosynthesis is reduced to zero in affected leaflets. As the spear unfurls, the beetle moves on to other palms or the next emerging spear. The beetle does not attack leaves that emerge un-damaged. Severe attacks destroy unopened leaves, affect growth of the palm and reduce its productivity. In most cases, all the central leaves of affected palms appear brown and fruit shedding is common in such palms. Stunted palms with less compact hearts are more susceptible to leaf beetle attacks. Damagecaused to millions of palms and substantial yield loss have been reported from countries infested by the beetle. A study commissioned by FAO showed that, if left uncontrolled, beetle infestations would cause in excess of US$ 1 billion damage in Vietnam alone.
Spread:The coconut leaf beetle spreads mostly through the movement of infested palms. Its natural spread is very slow since the beetles cannot fly long distances. Shipments of ornamental palms from infested countries have been the main source of spread within the Asia-Pacific region.
