Learn about the pests that damage citrus fruits and its control.
1. Bark Caterpillar, Indarbela Quadrinotata (Walker) (Lepidoptera: Metarbelidae):
The bark-eating caterpillars of the moth, I. quadrinotata feed on citrus, mango, guava, jamun, loquat, mulberry, pomegranate, ber, drumstick, litchi, amla, rose and a number of forest and ornamental trees. The pest is widely distributed in Myanmar, Bangladesh, Sri Lanka and India.
The freshly hatched larvae are dirty brown while the full-grown caterpillars (50-60 mm) have pale brown bodies with dark brown heads. The adults are pale brown moths with rufous head and thorax. The fore wings are pale rufous with numerous dark rufous bands. Their hind wings are fuscous.
Life-Cycle:
With the start of the summer season the moths emerge and become active. The females start laying eggs in clusters of 15-25 eggs each, under the loose bark of the trees. The egg laying continues throughout the summer. As many as 2000 eggs may be laid by a single female.
The eggs hatch in 8-10 days and the freshly hatched larvae nibble at the bark and after 2-3 days bore inside. The larvae have the habit of making webs along the feeding galleries and above the holes where they bore deeper into the wood. The galleries and the webs above them have a zig-zag shape and contain wooden frass and excreta.
The larvae take as many as 9-11 months to complete development. When full-grown, they make a hole into the wood and pupate inside. The pupal stage lasts 3-4 weeks. The moths emerge in summer and they are short lived. Only one generation is completed in a year.
The parasitoid, Zenillia haterusiae (Tachinidae) has been noticed attacking the larvae of this pest in Sri Lanka.
Damage:
Thick, ribbon like, silken webs are seen running on the bark of the main stem, especially near the forks. The larvae also make holes and as many as 16 holes may be seen on a tree, one caterpillar or pupa occupying each hole. A severe infestation may result in the death of the attacked stem but not of the main trunk. There may be interference with the translocation of cell sap and thus arrestation of growth of the tree is noticed with the resultant reduction in its fruiting capacity.
Prevention and Control:
(i) Clean cultivation is essential to prevent infestation of these borers,
(ii) As soon as infestation is noticed, kill the caterpillars mechanically by inserting an iron spike into the holes made by these caterpillars.
(iii) During February-March, insert into the borer holes insecticide- soaked cotton plugs (with the help of a metallic spike) and plaster on the outside with mud. The insecticides for 100 litres of water are 40 g carbaryl 50WP or 2 ml dichlorvos 100EC or 5 ml methyl parathion 50EC or 10 ml monocrotophos 40EC. These chemicals should be applied after removing webbings, and
(iv) Treat all alternate host plants in the vicinity of the orchard.
2. Fruit Sucking Moths, Ophideres Spp. (Lepidoptera: Noctuidae):
The fruit moths are minor pests of citrus, mango, grapes and apple, and are distributed throughout India. Ophideres conjuncta Cramer, O. Fullonica Linnaeus O.materna Cramer and O. ancilla Cramer are the commonest species found in Tamil Nadu, Madhya Pradesh, western Uttar Pradesh and Punjab. They are reported to be in abundance near the forests or other natural vegetation.
The presence of moths in a locality is observed from the characteristic pin-hole damage in citrus and other fruits. These moths are large and stoutly built and their prominent palpi are turned upwards. The piercing mouthparts are very well developed and are provided with sharp spines which help in puncturing the fruits.
The general body of O. conjucta is faint orange brown. Its fore wings are dark grey and the hind wings are orange red, having two black curved patches. The forewings in O. materna are pale greenish-grey with palish-white markings and the hind wings are orange brown, having marginal dark bands mixed with white spots.
The larvae are typical semiloopers and have a stout appearance. Their velvety dark brown background along with other patterns makes them cryptic. They have distinct eye-spots on the head, yellow or red lateral spots and a dorsal hump on the last segment of the body. A full-grown larva is 50-60 mm in length, and when disturbed, it assumes a characteristic posture by curving round the head and raising the hind part of its body.
Life-Cycle:
The moths are nocturnal and are not seen during the day. They lay eggs on a number of wild plants and weeds, namely Tinospora cardifolia, T. smilacina Benth, Cocculus hirsutus L, Cirsampelos pareira L, Convolvulus aruensis, Trichisia pattens Oliv. and Pericampylus glancus Blatter, which are often, found growing near citrus orchards. The eggs are round, translucent, measuring about 1 mm in diameter.
They hatch in about two weeks and within 24 hours of emergence, the young larvae start feeding on the foliage of host plants. A larva passes through five instars in four weeks. When full-grown, it makes a pupal case by webbing together pieces of leaves and soil particles. The pupa is thick-set and is dark reddish brown. This stage lasts about two weeks.
The moths, on emergence, fly to nearby orchards for feeding on fruit-juice. The exact duration of the life of the moth is not known. Most probably, the moths emerge in spring, when they start breeding. By July, the moths of the second brood are found in large numbers. They damage citrus plants up to October. The pupae of the third brood probably hibernate during winter.
Damage:
Unlike most moths and butterflies, the fruit-piercing moths cause damage in the adult stage. With the help of its strong, piercing mouthparts, moth punctures the fruit for sucking juice. Bacterial and fungal infections take place at the site of attack, with the result that the brownish mouth of a puncture becomes pale and eventually the whole fruit turns yellow. It drops off the tree and apparently looks like a premature fruit. If the damaged fruit is squeezed, the juice spurts from the hole. In severe cases of infestation, almost all the fruits are lost.
Prevention and Control:
(i) Systematic destruction of alternate host plants in the vicinity of the orchard is suggested to control this pest,
(ii) Dispose off fallen fruits which attract the moths.
(iii) Bagging of fruits is effective but very laborious and expensive,
(iv) Creating smoke in the orchards after sunset may keep the pest at bay, but this method is also cumbersome and not feasible on large scale.
(v) Spray trees with 2.5 kg of carbaryl 50WP in 500 litres of water per ha at the time of maturity of fruits,
(vi) Kill moths with a bait containing gur 1 kg + vinegar 60 g + lead arsenate 60 g + water 10 litres. Wide-mouthed bottles (1 bottle per 10 trees) containing bait solution should be tied to the plants when the fruits are in unripe condition.
3. Citrus Blossom Midge, Dasineura Citri Grover (Diptera: Cecidomyiidae):
This midge infests the blossom of many varieties of citrus in Punjab, Assam, Sikkim, Bengal, Andhra Pradesh, Maharashtra and Karnataka. The maggots cause damage to the developing flower buds which fall off. In the adult stage the minute flies are prominent owing to their orange colour.
Life-Cycle:
During the flowering season in February-March, the orange flies insert their stalked eggs in between the petals of flower buds. The eggs hatch in 32-40 hours and the larvae start feeding on unopened petals. They grow through four larval instars and this developmental stage is completed in 10-12 days. Then they descend to the soil, spin a silken cocoon and pupate there. The pupal stage lasts 4-6 days. During the flowering period of various citrus plants, two or three generations may be completed. The rest of the year is passed in the soil as a pupa.
Damage:
The attack of this pest is usually heavy during February-March and the infested blossom looks abnormal in shape. The attacked buds and flowers when shaken by wind drop off easily. Naturally the fruit bearing capacity of the trees is reduced very much.
Prevention and Control:
Spray 1.70 litres of dimethoate 30EC in 1250 litres of water per ha during August- September, when the pest may appear in severe infestation.
4. Citrus Leaf Folder, Psorosticha Zizyphi (Stainton) (Lepidoptera: Oecophoridae):
This pest has a country-wide distribution and is a common pest of citrus plants in central and northern parts.
Life-Cycle:
The eggs are laid singly or in groups along midribs of leaves. Up to 404 eggs are laid by a female moth. The egg, larval and pupal periods last 3-5, 9-11 and 5-10 days, respectively. The larva pupates in the leaf-folds. The adult lives for 5-16 days and the total life-cycle occupies 20-31 days.
Damage:
The pest is active in the nursery and young plantations from May to October. The larvae web together and fold leaves and start feeding from top to downwards. They feed from within on the epidermis first and on the whole leaves later. The plants become stunted.
Prevention and Control:
Spray 1.5 litres of monocrotophos 36SL or 3.125 litres of chlorpyriphos 20EC or 2.5 litres of quinalphos 25EC in 1250 litres of water/ha.
5. Citrus Aphid, Toxoptera Spp. (Hemiptera: Aphididae):
The brown citrus aphid, Toxoptera citricidus (Kirkaldy) and the black citrus aphid, T. aurantii (Boyer de Fonscolombe) are important pests of citrus, the former being a vector of citrus tristeza virus. T. citricidus is widely distributed in South America, Central America, South and Southeast Asia. In India, Toxoptera spp. is widely present on Coorg mandarin and also on Nagpur mandarin.
The host plants of these aphids include various species of the Rutaceae and Rosaceae families. The adult wingless forms (apterae) of T. citricidus are shiny black and nymphs are dark reddish brown. The adult winged forms (alatae) can be recognized by the conspicuous black antennal segments I, II and III. The nymphs of brown aphid give out yellow haemolymph and black aphid, red haemolymph on squashing.
Life-Cycle:
The aphids are usually present on citrus throughout the year. However, they are most abundant in the spring and autumn. They are active from first week of February to first week of May, with their critical period of infestation from first week of March to first week of April.
The citrus aphid produces about 5 young ones daily for a period of 1-3 weeks parthenogenetically which attain maturity in about 6 days. Winged colonizing adults called ‘stem mothers’ give birth directly to nymphs with no egg stage and no mating required. When citrus trees flush, the alate adults fly into the orchards, infesting the new shoots and producing nymphs by means of viviparity. The nymphs take 6-42 days to complete 4 molts before becoming adults. Each female can produce 5-68 nymphs. The adults live for 5-25 days. Alate forms appear as a result of crowding. It completes 9 overlapping generations in a year.
Damage:
The nymphs and adults suck the cell sap from young leaves and tender twigs. This impairs the vitality of the trees. The affected leaves in severe cases curl up and get deformed. The growth of young shoots is adversely affected resulting into stunted growth. Blossoms and newly set fruits are also attacked. The honeydew excreted by the aphids also provides a good substrate for the growth of sooty mould, which affects the photosynthetic activity of the plants.
Prevention and Control:
(i) Release of the coccinellid predator, Menochilus sexmaculatus (Fabricius) @ 50 per tree helps to suppress the aphid population.
(ii) Chemical control measures are same as in case of citrus psylla.
6. Citrus Mite, Oligonychus Citri McGregor (Acari: Tetranychidae):
This pest of citrus is of international importance and has been recorded in USA (especially in Florida and California), Indonesia, the Philippines, Israel, Iraq, Iran, UAR, Sri Lanka and India. It was first recorded in southern India where it was found along with Tetranychus sexmaculata Riley, T. urticae Koch and T. hindustanicus Hirst. In the Punjab, it is found infesting sweet-orange, lemon, grapefruit and sour-lime. No alternative hosts of this mite are known.
The citrus red mite has been recorded as a pest of citrus at Abohar in Punjab where there are large citrus orchards. All the feeding stages cause damage by sucking cell-sap from the leaves. The adult is small, plump and orange with thick deep brown patches on the dorsal side of its body and measures 0.33 mm in length.
Its body is covered with prominent bristles, each borne on a whitish tubercle. The antennae of the females are three segmented and are bright carmine pink. The newly hatched larva is light yellowish brown and has only three pairs of legs. The protonymph is orange brown and the duetonymph is orange brown with a greenish tinge.
Life-Cycle:
This pest is active throughout the year but exhibits slower breeding in the winter. The mites are most active during May-June when they lay about 50 eggs each, arranged singly along large veins on the underside of the leaves. The eggs are minute, round and orange, and are embedded in the leaf tissues with ornamentations of threads which extend from the top outwards.
They hatch in about one week. Those eggs laid by unmated females, develop into males, whereas those from the mated females, develop into a mixture of females and males. The first instar larva has three pairs of legs and after feeding on the cell-sap for three or four days, it moults into a protonymph which has four pairs of legs.
In 3-4 days, it develops further to form the duetonymph which also has four pairs of legs. It is full-fed in 4-5 days and after moulting, transforms itself into an adult mite. The female mites live for about ten or more days. The life-cycle in summer is completed in 17-20 days and the pest passes through several overlapping generations in a year.
Damage:
Mites are considered to be highly destructive pests of citrus plantations. Injury to leaves, tender fruits and green bark is caused by their constant feeding on chlorophyll, resulting in a speckled appearance of the leaves. Heavy infestation may result in complete defoliation, especially of the young nursery plants. The affected fruits become yellow and remain undersized.
Prevention and Control:
Spray 2.5 litres of ethion 50EC or 1.875 litres of fenzaquin 10EC in 1250 litres of water/ha as soon as the mite population appears on the underside of the leaves. Repeat the spray if needed.
7. Lance Nematode, Hoplolaimus Indicus Sher (Nematoda: Hopioiaiminae):
This plant parasitic nematode was first recorded in India during 1963 and its presence and prevalence in citrus orchards and tomato fields was confirmed in 1966. Further studies have proved its widespread distribution on a variety of crops in Punjab. These nematodes feed on root tissues for a short time, like an ectoparasite, and then they retreat into the surrounding soil medium. No part of the development is completed inside the plant tissues.
Life-Cycle:
The oblong eggs which measure 70-75 microns in length and 30 microns in width are deposited in the two-celled stage. Further development of the embryo continues inside the egg and the first stage larva is visible in about 13 days after the deposition of eggs. The larva emerges from the egg when it is in the second stage and starts feeding immediately after emergence.
To attain full growth, the larva passes through five stages. The life-cycle is completed within 42-99 days (temperature 20-35°C.). The development of various stages is quickest at 30°C, which is also the optimum temperature for the survival of various stages and for egg-laying.
The optimum pH range for the development of various stages is 6-8 and the maximum increase in population takes place at pH 7. The optimum soil moisture is about 16 per cent. Light soils are more suitable for reproduction. Sandy-loam soil provides the optimum conditions.
Damage:
The population of this nematode is highest in April in citrus orchards. Old citrus plants (10 years of age or more) carry more population. The maximum population occurs upto a depth of 15 cm from the surface. The nematode has a high population in tomato fields, often reaching pest proportions.
The incidence in citrus orchards has not yet attained the pest level in most places. Thus, there is great need to suppress this nematode before it imposes itself as a serious pest on citrus plants. Of various other plants, the nematode seems to prefer tomato, brinjal, maize and sugarcane. Tobacco, mustard, peas, sugar-beet, water-melon and guava are unsuitable hosts.
8. Citrus Nematode, Tylenchulus Semipenetrans (Cobb) (Tylenchida: Tylenchulidae):
This nematode is associated with the problem of citrus decline. The plants become unprofitable because their fruit set is lowered and the incidence of fruit-drop is increased. This citrus nematode was detected as a pest as early as 1913 in the USA and is widely distributed in practically all the citrus-growing regions of the world. In India, it has been recorded in Punjab and Delhi. The moving of nursery stock is the commonest means of carrying this nematode from one country to another.
Life-Cycle:
The female nematodes are found on thick, stunted rootlets to which a layer of soil particles might be adhering. These particles are held in place by gelatinous mucus secreted by the females. This mucus normally forms a protective covering around them. The females retain the eggs inside till segmentation in the embryo is demarcated.
The eggs hatch in about two weeks and the larvae start feeding on the rootlets. The larvae destined to be males or females have two distinct periods of development. Those which are short and rather broad develop to form mature males without any feeding; the others are slender and feed on plant roots for 6-8 weeks before developing into females.
The most interesting point about this pest is that, in the absence of mating with males, the females are capable of reproducing. These females produce eggs which further give rise to normal males and females. In citrus-growing areas, several generations are completed in a year. It is estimated that if there are 1,500 nematodes per 500 g of soil, the pest can cause appreciable damage to the citrus plants and produce symptoms of tree decline.
Damage:
The first indication of injury by this pest is a reduction in terminal growth, followed by a general reduction in vigour, yellowing and drying of leaves and twigs. The trees just survive and produce a reduced crop of inferior fruits.
Prevention and Control:
(i) The introduction of this pest into new areas can be checked by using clean nursery stock obtained from those places where the soil has been thoroughly fumigated,
(ii) Use Nemagon @ 25 litres per ha. Pulverise soil in the basin area around a plant and mix the chemical thoroughly followed by flood irrigation.