Learn about the defoliators of forest trees and its control.
The foliage of trees provides food to large varieties of insects such as the leaf-miners, leaf rollers, leaf feeders, sap suckers, gall producers, etc. The overall effects of all these insects on the health of the trees are the same, namely, a serious attack may kill the trees, a moderate one depilate them and adversely affect the quality of wood they produce.
1. Teak Defoliator, Hyblaea Puera (Cramer) (Lepidoptera: Hyblaeidae):
The teak defoliator is commonly found in South India, Western Ghats, Maharashtra and Uttarakhand. This pest has also been reported from Australia, Myanmar, Sri Lanka, Java, Southern USA and Africa. This is oligophagous pest, but teak (Tectona grandis) is its principal host.
Its alternative hosts are scattered in the families Verbenaceae, Bignonaceae, Araliaceae, Jugalandaceae and Oleaceae. The moths are with greyish brown fore wings, and hind wings are with black and orange- yellow markings. It has wing span of 3-4 cm. Larvae are defoliators. Pupae are brownish and object type.
Life-Cycle:
Mated female lays her eggs singly near the veins on the under surface of the tender leaves. A single female can lay about 400 eggs. The eggs hatch within two days and newly emerged tiny larvae feed on the tender leaves of the teak plant. The larva moults for 5 times and prefers only young and tender leaves of teak for feeding. Larval stage lasts for 10-12 days or may extend up to 20 days in cold weather.
The full-grown larva descends down on the ground with the help of silken threads and pupates in soil or in litter. Depending upon climatic conditions, pupal stage lasts for 4-8 days. The whole life-cycle is completed within 19-36 days. The life-cycle period is extended in cold weather. Many generations are possible in a year.
Various parasitoids, viz. Brachymerciia lasus (Walker). Eriborus gardneri (Cushman), Plalexorista sp. and Symplensis sp. cause about 70 per cent mortality in the larval stage of the pest.
Damage:
Only the caterpillars are destructive. They feed on tender leaves of teak and affect the growth of the plant. The pest causes about 44 per cent damage.
Control:
(i) Collect and destroy the egg masses, larvae and pupae.
(ii) Clean cultivation and digging the field for exposing pupae to natural mortality factors, is helpful in reducing the incidence of the pest.
(iii) Bacillus thuringiensis and nuclear polyhedrovirus play an important role in suppression of the pest.
(iv) Pheromone traps may be utilized to attract and kill the pest.
2. Teak Skeletonizer, Eutectona Machaeralis (Walker) (Lepidoptera: Pyralidae):
The teak skeletonizer is prevalent in Western Ghats, Maharashtra, Uttarkhand, Andhra Pradesh, Tamil Nadu and Karnataka, Outside India; it has been recorded from Australia and Indonesia. The pest attacks teak (Tectona grandis) and some species of Callicarpa.
The moths are bright yellow with fulvous or pink transverse marking of zigzag pattern or serrate lines on the white fore wings. The hind wings are pale with ocherous or reddish marginal line or band. The pattern and colour of wings vary with the temperature and humidity.
Life-Cycle:
The mated female lays her eggs singly on tender leaves of the teak plant. A single female can lay about 250 eggs on the underside of the leaves. The eggs hatch within few days and the newly emerged larvae feed on tender leaves of teak. The larvae feed on the entire green matter of the leaf leaving veinlet network intact, thereby riddling the leaf. All instars can feed on young and older leaves of the plant. There are five larval instars. The last instar larvae pupate along with fallen leaves. The pest hibernates from January to March. The life-cycle is completed within one month.
Trichogramma minutum Riley, T. brasilensis (Ashmead) and T. evanscens Westwood attack eggs of the pest, whereas Cedria paradosa parasitizes the larvae.
Control:
The caterpillars feed voraciously on the tender and old leaves, and skeletonize the plant affecting the growth.
3. Pink Gypsy Moth, Lymantria Mathura Moore (Lepidoptera: Lymantriidae):
The pink gypsy moth is widely distributed in Western Ghats, Assam, and Himalaya region, Uttar Pradesh, Uttarakhand and Sikkim. Outside India, it has been recorded from Japan, USA and several Asiatic countries. This pest occurs in cool, temperate to warm climates and in fixed forests, temperate coniferous, tropical and subtropical broad leaf dry forests and moist broad leaf forests. It is a polyphagus pest and damages a large number of plants belonging to 45 genera of 24 families. Important host plants include sal, asna, Australian red cedar, zelkowa, cherry, willow, peach, apple, ash, walnut, oak, pine, chestnut, wax tree, etc.
The male moth shows black spots on vertex. The ground colour of fore wing is paler and dorsal side is black with zigzag markings. Hind wings are orange with black spot at the end of cell and conjoined series of sub-marginal spots showing a curved band. Females are characterised by having head and thorax white, frons fuscus and two black spots on vertex. Abdomen is crimson red with small black spots on vertex.
Fore wings are white with crimson and black spots and with typical zig-zag marks. Hind wings are crimson with fuscus spots at the end of the cell. A sub-marginal maculate band is present on hind wing with some spots on centre of margin. The wing expanse of male is 40-51 mm and that of female is 96-112 mm. The larva is brownish with full of hairs on the body.
Life-Cycle:
The females lay eggs on leaves of the host plants. Hundreds of eggs are laid by a single female in batches or in clusters. Eggs hatch in March/April. The larvae are gregarious feeders. The larva passes through 5-6 instars, and the total larval period is about 85 days. The full-grown larva pupates in soil and the pupal period lasts for 10-15 days. Only one generation is completed in a year.
Damage:
The caterpillars feed gregariously on flowers and leaves, and skeletonize the plant completely in severe infestation. Young shoots are completely destroyed and many times total loss is not uncommon.
Control:
(i) Collect and destroy the eggs masses, and gregarious and solitary larvae.
(ii) Dig soil for exposing pupae to natural mortality factors.
(iii) Use pheromone traps f catch and kill the moths.
(iv) Use light traps; the moths are attracted to black coloured traps.
(v) Spray the crop with azadirachtin (0.03%) or DDVP (0.03%)
4. Indian Gypsy Moth, Lymantria Obfuscata Walker (Lepidoptera: Lymantriidae):
The Indian gypsy moth is distributed in Himachal Pradesh, Uttarakhand, North West Himalaya, and Jammu and Kashmir. The insects feed on a number of hosts including willow, poplar, apricot, apple and walnut. The male moth is greyish brown with wing expanse of 32 mm, Fore wings are with post-medial double lines more regular and hind wings are with dark lunule at the end of cell. The larvae are pale brown with short dorsal tufts of hair and long lateral tufts. The larva also shows a dark brown dorsal band with lines down the centre and on each side. Full-grown larva measures about 40-50 mm in body length.
Life-Cycle:
The female lays eggs in batches on the bark in June and July. Eggs are rounded, shining and light greyish brown. Each batch consists of 200-400 eggs and covered by yellowish brown hair. The winter is passed in egg stage and the eggs hatch in March or early April. Newly emerged larvae feed gregariously on leaves.
The larva moults Five times and is full-grown within 6-14 weeks depending on climatic conditions. The full-grown larvae gather on the bark of the tree on under surface of branches and under the debris and stones, and pupate in the soil within the debris. The pupal stage lasts for 9-21 days. Only one generation is completed in a year Males survive for 4-10 days and the females for 11-31 days.
Damage:
The caterpillars are the only destructive stage of the pest and they feed on leaves gregariously and skeletonize the plant in severe infestation. The caterpillars are voracious feeders and they feed at night. It is a serious pest of willow in Kashmir Valley and North West Himalayas.
Control:
(i) Collect and destroy the egg masses and gregarious forms of caterpillars.
(ii) Provide shelter for full-grown larvae at the base of tree trunk and later remove or collect and destroy the larvae.
(iii) Clean cultivation for exposing larvae to natural mortality factors is useful.
(iv) Dig the crop for exposing pupae to natural mortality factors.
(v) Treat the crop with dimethoate (0.03%) or phosphamidon (0.03%) or carbaryl (0.15%).
5. Deodar Defoliator, Ectropis Deodarae Prout (Lepidoptera: Geometridae):
The deodar defoliator has been found infesting deodar (Cedrus deodcira) in Uttar Pradesh, Kerala and Punjab. It has been recorded at higher altitudes, above 1500 metres. Moths are medium sized with fore wings and hind wings poorly developed and with numerous irregular black spots. Eggs are rounded and full-grown caterpillar measures 2-3 cm in body length. The pupa is brownish and objects type.
Life-Cycle:
Drapausing pupae emerge as moths in spring and moths mate immediately after emergence. Mated females then start climbing on the deodar tree for egg laying on the needles of the tree. Eggs are laid in mass and they hatch within 2-5 days in spring. Newly emerged larvae start feeding on the needles of the deodar and moult 5-6 times. Full-grown larvae descend to the ground for pupation. The larvae pupate on the ground within the fallen needles or in soil under a layer of humus. The pest hibernates in pupal stage.
Damage:
The caterpillars are the only destructive stage of the pest. The caterpillars are most injurious to deodar tree since they feed on the needles. In case of severe infestation, they skeletonize the whole plant.
Control:
(i) Collect and destroy the egg masses and the caterpillars.
(ii) Dig field under the shade of the tree for exposing the pupae for natural mortality factors.
(iii) Clean cultivation for exposing pupae to biotic and abiotic factors helps in suppression of the pest.
(iv) Use shrews in forest against mature larvae and pupae of this pest.
(v) Encourage birds against larvae and pupae of the pest.
(vi) Spray the crops with azadirachtin (0.03%) or dust the crop with carbaryl 5 per cent @ 25 kg per ha.
6. Shisham Defoliator, Plecoptera Reflexa Guenee (Lepidoptera: Noctuidae):
The shisham defoliator occurs on shisham in Punjab, Maharashtra, West Bengal, throughout North India and Andamans. The moth is grey brown with bright fulvous head and collar, and has a wing span of 30-35 mm. Fore wing contains a large reniform spot with black centre and with a rufos spot on the costa.
The marginal series of minute dark specks is the characteristic of the fore wing. The hind wing is fuscus brown with outer area slightly darker. Males show fuscus area on costal margin of hind wing. The caterpillar is a green semilooper turning pinkish and measuring about 25 mm long when grown.
Life-Cycle:
The female moth lays eggs on tender leaves and a single female can lay about 400 eggs. Eggs are laid in clusters and they hatch in 4-6 days. On hatching, the larvae feed on the tender leaves of shisham. There are 5-6 larval instars and the larval period lasts for 14-21 days. Full- grown larvae descend to the ground and pupate within the fallen leaves.
Shisham defoliator is attacked by several parasitoids, viz. Euplectrus parvulus Ferriere (early larval instars), Disoplirys sissoo Wilkinson and Microgaster plecopterae Wilkinson (larvae), Exorista civiloides Baranov, E. picta Baranov and Podomvia setosa Doleschall (both larvae and pupae), and Brachymeria nursei (Cameron)(pupae). The levels of parasitism range from 2-24 per cent.
Damage:
Plantations about three years old and above are attacked by this pest. In repeated severe attacks, tree remains leafless for the greater part of the growing season and epicormic branches are produced. In case of severe defoliation, poor quality plantations have often been abandoned or converted. Defoliation is severe in roadside and canal-bank plantations but not in gregarious natural stands.
Control:
(i) Collect and destroy clusters of egg masses and gregarious and solitary caterpillars from the leaves.
(ii) Dig the soil near and under the shade and base of the tree for exposing pupae to natural mortality factors.
(iii) Use natural enemies like shrews and predatory birds.
(iv) Spray carbaryl (0.15%) or azadirachtin (0.03%).
7. Kadam Defoliator, Arthroschista Hilaris (Walker) (Lepidoptera: Pyralidae):
The kadam defoliator has been recorded in India, Malaysia and the Philippines on kadam (Neolamarckia cadamba). The bluish green moth has a wing span of about 34 mm. The mature larva is pale green with a dark brown head capsule, and about 25 mm long with inconspicuous hair.
Life-Cycle:
The female moth lays 60- 70 eggs, singly or in groups of two or three, on leaves. There are five larval instars. The first and second instar larvae feed on soft leaf tissue under cover of a silken web. The later instars eat out the entire leaf blade between the veins, under cover of a partial leaf fold.
The larval development is completed in about 15 days and pupation takes place inside the silken web. The total life-cycle is completed in 21-26 days. In India, the insect can complete 11-12 generations a year in West Bengal and 8-9 in Uttarakhand, where the larval period is prolonged in the winter.
Natural enemies include six hymenopteran larval parasitoids, three hymenopteran pupal parasitoids and a few reduvid, carabid and ant predators. Apanteles balteatae Lai was reported to parasitize up to 60 per cent of larvae during peak incidence of the pest in West Bengal and A. stantoni Ashmead up to 50 per cent of larvae in Sabah, Malaysia. Other larval parasitoids include Cedria paradoxa Wilkinson, Macrocentrus philippinensis Ashmead and Sympiesis sp.
Damage:
Feeding of the early instars on the leaf surface causes browning of leaves, while consumption of the leaf blade by older larvae leads to shedding of leaves. In defoliated trees, the larvae feed on the soft terminal shoot, causing dieback and formation of epicormic branches.
The growth of saplings is adversely affected, although the plants seldom die. Peak infestation in West Bengal occurs during the post-monsoon period in August-September, during which moderate to heavy defoliation occurs. At Saba in Malaysia, population peaks have been recorded twice a year, in April-June and November-January.
Control:
(i) Clean cultivation to expose the pupae to natural mortality factors helps to check this pest.
(ii) Encourage the natural enemies to suppress the pest.
(iii) Spray carbaryl (0.15%) or azadirachtin (0.03%).
8. Gamhar Defoliator, Craspedonta Leayana (Latreille) (Coleoptera: Chrysomelidae):
The gamhar defoliator has been recorded as a pest of Gmelena arborea in India, Bangladesh, Myanmar and Thailand. In India, it is prevalent in the northern region but also occurs in central and southern regions. The beetle is 12-16 mm long and has a brilliant metallic colouration, with coarsely wrinkled, bluish green to violet elytra and pale yellow to reddish brown pronotum and legs.
The larva has a typical appearance, with lateral spines. The excrement, instead of being ejected, is extruded in fine, black filaments, longer than the body, and formed into bunches attached to the anal end. When disturbed, the larva flicks the anal filaments up and down, and assumes a defensive posture.
Life-Cycle:
Eggs are laid in clusters of about 10-100 (average 68), on the under-surface of leaf or on tender stem and are covered by a sticky, frothy secretion which solidifies to form a domed, brownish ootheca. The opposition period may range up to 45 days, with an average fecundity of 874. The larvae are gregarious and there are five larval instars.
The larval period is completed in about 18 days under optimal conditions. The full-grown larva fastens itself to the leaf by the first three abdominal segments and pupation occurs on the leaf itself. Under favourable conditions, the life-cycle is completed in 35-50 days, but third generation adults enter into hibernation in winter.
Damage:
Both the adult and the larvae feed on leaves. The early instars feed by scraping the surface of the leaf but later instars and the adult feed by making large, irregular holes on the leaf. Even young shoots are eaten up when the population density is high. Heavy attack causes total defoliation and drying up of the leader shoots in young trees, leading to severe growth retardation. With two or more consecutive complete defoliations, the tree is likely to be killed.
Control:
(i) Collect and destroy the egg masses and gregarious larvae.
(ii) The population of adult beetles can be checked by trapping them in artificial hibernation shelters.
(iii) Hand-picking of beetles returning to the plantation after overwintering helps in pest suppression.
(iv) Commercial preparations of Bacillus thuringiensis subsp. kurstoki and Beauveria bassiana have been shown to be effective against the larvae.
(v) Spray the crop with DDVP (0.05%) or quinalphos (0.04%).