WHITE GRUB

CLASSIFICATION

Distribution: In India (abundance in sandy loam tracts of Kerala and Karnataka)

Main Host: Coconut

Occurrence: Frequently September to October. The adult beetles emerge from the soil after pre monsoon showers in May – June.

Life Cycle:

Adults of L. coneophora is medium sized reddish brown to chestnut colored beetles measuring 20 – 45 mm long and 13 – 20 mm wide. Eyes are black and protruding. Body, appendages, elytra are covered with oval pointed yellowish brown scales and scattered amongst these are bigger and elongate oval white scales. The antenna is eight segmented including the lamellate club with joints closely co – adapted.

Egg is oval in shape and creamy white in color when freshly laid and measures 5 mm long and 4mm broad. Prior to hatching they turn to dirty white.

The grubs are curved, fleshy and wrinkled. They are creamy white in color with brown head. Mouth parts are strong with conspicuous mandibles. The last abdominal segment is enlarged and ventrally bears two longitudinally rows of short spinules called as radular spines or raster. The larvae when fully grown, measure about 60 mm in length and 12 mm in breadth. The larvae become yellowish, stops feeding and constructs a boat shaped pupal chamber in the soil and pupate.

Adult emergence commences with 3 – 5 pre monsoon showers in May – June. The peak emergence takes place at dusk at about 18.30 hrs. and emerged adults are active in the field for about half an hour (mating takes place during this time). Circular emergence holes of about 12 – 14 mm in diameter could be noticed during the emergence season in the infested gardens. The adult longevity is about 30 days.

Damage:

In coconut nursery, the grubs feed on the tender roots and tunnel into the bole of the collar region resulting in drying up of the spindle followed by yellowing of the outer leaves and gradual death of the seedling. In older coconut plantations continuous infestation by the grub results in yellowing of leaves, premature nutfall, delayed flowering, retardation in growth and reduction in yield. In addition to coconut, they also cause damage to the tuber crops raised in the interspaces like tapioca, colocassia, dioscoria etc. The damage to root system causes general debility of the palm and resultant crop loss.

Management:

•  Repeated ploughing once a week for 4 – 5 times after first rains in summer reduce the pest population by exposing the pest to predation by birds and other animals.

•  Collection and destruction of adult beetles during peak period of emergence in May – June.

•  Apply phorate 10 G @ 100g / Palm in May – June and September – October ie prior to pre and post monsoon periods. In places where the copious rainfall is during September to November, the application may coincide with rainfall.