Citrus trees are attacked by many pests. The world list of citrus insects and mites contains 823 species of which over 20 percent are found in India. In Punjab itself 22 species have been recorded and 14 of these are pests of economic importance. These vary considerably in importance with regard to citrus decline. In this article we have mentioned only those insect species which may contribute towards citrus decline.
1. Citrus Psylla
Of all pests of citrus in Punjab, citrus psylla, Diaphorina citri Kuwayama, is of utmost importance. It is widely distributed throughout tropical and subtropical Asia and the Far East and has been recorded from West Pakistan, India, Ceylon, Burma, Mlaya, Indonesia, Southern China, Macao, Taiwan, and the Philippines. Citrus psylla attacks all species and varieties of citrus and is also recorded to attack muruwa or Murraya koenigii Speng in India and wampee or Clausena Lansium in China.
Both nymphs and adults suck the plant and cause damage, but the former stage alone causes significant damage. They suck huge quantities of sap from tender growing shoots which as a consequence dry up. In addition, this insect probably injects certain toxins with its saliva because even branches other than those actually attacked are reported to dry up.
Treatment:
“During the first year damage is not very marked, but yield falls and some top branches dry up. During the second year the new shoots are destroyed, most of the branches are left without leaves and tree begins to dry up; very little fruit is borne and that too is insipid and dry. During the third year there is neither leaf nor fruit.
Income figures from two orchards for 1915-1920 in Sargodha out at Abohar using some newer insecticides, and in the year 1964-65, parathion,diazinion, methyl demeton, Bidrin and endrin (all as 0.02% emulsions), malathion 0.05% emulsion, and carbaryl 0.1% suspension proved to be equally effective. In subsequent trials the more promising insecticides in decreasing order of effectiveness were phosphamidon 0.025%,parathion0.025%,malathion 0.03% + DDT 0.15% and malathion 0.05% in case of the nymphs, and parathion 0.025%, DDT+bhc 0.1% each; malathion 0.05% and phosphamidon 0.025% in case of the adults; and as a result phosphamidon 0.025%, parathion 0.025%, and malathion 0.05% were recommended.
2. Citrus White-Flies
Of the 30 species of Aleyrodidae on citrus throughout the world, 12 are found in India and the following 8 species can be seen within the Punjab region.
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Hussain’s white- fly
Aleaurocanthus husaini Corbett
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Orange spiny white-fly
A.Spiniferus (Quaintance)
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Citrus black-fly
A.woglumi Ashby
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White-fly
Aleurolobus citrifolii Corbett
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Marlatt’s white-fly
A.maelatti (Quaintance)
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Citrus white-fly
Dialeurodes citri(Ashmead)
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Elongate white-fly
Dialeurolonga elongate Dozier
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White-fly
Aleurotuberculatus murrayee Singh
Different species vary in their breeding habits. The more important among them, viz., Dialeurodes and Aleurocanthus spp., habe 2-3 broods, the first in March-April and the second and third in July-August to October, but Aleurolobus spp. Breed continuously from March to December. The adults of white –flies are minute ceatures with mealy wings held over the body in a roof like manner. White fly adults are more active at dusk and tend to rest on the lower surfaces of tender leaves during the day. The eggs are extremely minute and hardly visible to the naked eye. However, much damage is invariably caused before these agencies are able to bring the pest under control and it is necessary, to resort to artificial measures.
Treatment
Saini (1964) studying the effectiveness of DDT, parathion, and isobenzan for the control of this pest found that DDT 0.1%, endrin and parathion at 0.01%, and isobenzan 0.02% gave 100 percent kill of the adults. In the control of third instar nymphs, isobenzan, parathion, and endrin 0.03% emulsions proved very effective while DDT was not so effective. For the destruction of eggs and pupae only parathion, 0.03% proved effective. Considering these results, a 0.03% emulsion of isobenzan, parathion, or endrin should prove more effective than DDT 0.1% suspension spray which has been the previously recommended practice.
3. Scales and Mealy-bugs
49 species of scales and mealy-bugs on citrus in India and at least 8 of these sucking insects are known occasionally to infest citrus trees in the Punjab. These can be classified as follows:
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California red scale
Aonidiella aurantii (Maskell)
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Oriental yellow scale
orientalis (Newstead)
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Florida red scale
Chrysomphalus aonidum (L.) Syn.C.ficus Ashmead
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Glover’s scale
Lepidosphes gloverii (Packard)
The mango mealy- bug is best controlled by using a 7-8 cm. wide sticky band applied around the trunk at a height of 0.5 meter from the ground during the second week of December. This barrier traps most of the nymphs that attempt to ascend the tree. The crust formed by the hardening of the adhesive should be removed and the band renewed when found necessary. The nymphs congregating below the band may be killed by spraying with 0.1% methyl parathion emulsion or with the aid of a blow lamp. Raking of the soil under the trees during summer exposes the eggs to desiccation and natural enemies. Mealy-bugs and scale insects, especially armoured scales, are very difficult to kill with insecticidal sprays and low volume concentrate sprays have not proved very effective in their control.
Treatment
In California most of the citrus are controlled by sprays of malthion (25% w.p. 2.5 to 3.5 lb/100 gallons); parathion (25% w.p. 1.5-2.5lb/100 gallons);malathion+parathion (1/2 dosage of each); oil emulsions (2 gallons/100 gallons) of malathion or parathion in oil emulsions. In India mixing of Albolineum No. 1 + Tenac (a sticker) with parathion has been reported to enhance the toxicity of parathion to citrus scales. In tests conducted in 1962 at Sarai Naga, parathion 0.03% emilsion spray proved to be quite effective.
4. Aphids
Following four species of Aphids has been reported among citrus pests in India.
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The green apple aphid, Aphis pomi de Geer, reported as Dorsalis pomi( de Geer)
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The green peach aphid, Myzus persicae (Sulzer)
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The brown citrus aphid, Toxoptera citricida (Kirkaldy)
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The black citrus aphid, Toxoptera aurantii mispelt as T. amranti
Treatment
Aphids breeding on citrus can be easily controlled. BHC 0.25 %, menazon 0.2%, nicotine sulphate 0.05%, parathion 0.03% and malathion 0.03% to be effective for control. Some other insecticides like phosphamidon 0.025% solution, methyl demeton 0.0255 or dimehoate 0.0255 emulsions should also prove very effective.
However, in our arsenal we do not have either a strong repellent which may repel effectively the migrating aphids from settling on citrus trees, or an insecticide with an extremely quick knock-down action to kill aphids in a few seconds while at the same time having long residual action.
