Rugose Spiralling Whitefly (RSW) (Aleurodicus rugioperculatus Martin) is an invasive pest on coconut reported from Polalchi, Tamil Nadu and Palakkad, Kerala during July-August 2016. Reported first from coconut during 2004 at Belize, the pest had threatened coconut palms in Florida during 2009. As a polyphagous pest with more than 200 host plants, entry of the pest has been viewed seriously in the coconut growing regions of South India. Reports have started coming on its occurrence from Andhra Pradesh also.
About the pest
RSW is a small sap sucking insect belonging to Hemiptera Order which is taxonomically related to mealy bugs and aphids. The adult whitefly looks like a very small moth and have a body length of about 2 mm. Wings of adults are white and have dark spots on the forewings. Adults have greyish eyes. The males are slightly smaller than females and have elongate claspers at the distal end of the abdomen. Eggs are elliptical and yellowish in colour, 0.3mm long, translucent with a short stalk and are laid singly and associated with irregularly spiralling deposits of white flocculent wax surrounding each egg in a semi-circular spiralling fashion. The spiralling of waxy material is the feature from which its common name, spiralling whitefly is derived. Adult whiteflies had opening on the ventral side through which the white flocculent material emerges out. The first-instar crawlers are the immature stage with functional legs and distinct antennae and are mobile. Subsequent larval stages are sedentary and have oval shaped soft bodies with cream colour studded with white waxy material on the sides. The final immature stage is the pseudo-puparium, which is about 1 mm in length and is used in taxonomic identification.
Nature of damage
The immature and adult whitefly by their sucking feeding habit, siphon out coconut sap by selective feeding on the undersurfaces of the leaflets. Extensive feeding of the insect leads to the excretion of honey dew which subsequently gets deposited on the upper surface of the leaves positioned down beneath or even on other under storey crops. Honey dew excrement, being sweet and watery, attracts ants and encourages growth of the fungus Capnodium sp. which causes disfigurement of hosts affecting the photosynthetic efficiency of the plant. Since the outer whorl of fronds of coconut palm, which already bear coconut bunches of different maturity, do not contribute to the nut yield considerably, the whitefly infestation with minimum tissue damage and sooty mould on the outer whorl of fronds may not result in yield loss. Since the black tinge on crop plants (sooty mould) are mere sugar feeding fungus, farmers need not be worried about such tinge on crops plants as they are not poisonous. Waxy flocculent material produced by the adult whiteflies, however, can be another nuisance to human beings, as they get dispensed with a fluff of white dust, the moment insects are disturbed. Despite heavy incidence of whitefly on coconut, it is not practically causing any economic crop loss and, therefore, there is absolutely no need for any panic. In the recent survey conducted in heavily affected gardens, cutting across all age groups of palms, as high as 60-70% of the fronds was found infested by the pest. The prevalence of the pest was noticed from the outer whorls and slowly progressed towards the inner whorls, whereas, the emerging fronds were not infested.
In the recent survey, we could observe at least ten alternate host plants (Psidium guajava; Musa sp., Myristica fragrans; Colacasia sp., Garcinia sp., Annona muricata; Murraya koenigii; Spondias mombin; Mangifera indica andArtocarpus heterophyllus)in coconut homesteads, but the pest is relatively more confined to coconut and the reason for its selective preference more aligned towards coconut indicates its host preference to coconut.
The shift in weather pattern reflected as deficit monsoon could be one of the primary reasons of immediate upsurge of spiraling whitefly. They are so sensitive to wet season and heavy rains and the recent deficit in monsoon (>35% in Kerala), which triggered a drop in relative humidity (up to 7% compared to the previous year), is the immediate reason for the flare up. Increase in temperature over 2oC during summer is another pre-disposing factor for the increase in pest population. Emergence of sucking pest as a victim of climate change, thus, warrants close scrutiny. As coconut is a the homestead crop in Kerala with intercrops such as banana, vegetables, curry leaf, tapioca, etc. grown along with it, the sooty mould developed on coconut and other crops is of concern to the farmers.
In the present investigation, we could observe that more than 50% of the whitefly was parasitized by a tiny hymenopteran parasitoid, Encarsia sp. (<1 mm size) from different tracts of Kerala indicating the natural build of the parasitoids. This is one of the classical biological control strategies and any disturbance in the buildup of Encarsia sp. would invariably affect the long term approach in pest bio-suppression. In addition, lady beetles belonging to Jauravia sp. and a wide array of spiders were also noticed. With the emergence of A. rugioperculatus in coconut and natural build up of Encarsia sp. in Kerala, it could be well understood that the pest-defender system should be carefully conserved in the region so as to encourage population build up of the natural enemies. Fortuitous introduction of Encarsia sp. along with the pest or wide-range parasitic ability of the indigenous Encarsia sp. will be ascertained once the species is identified. However, the co-evolutionary occurrence of the parasitoid Encarsia sp. with the dynamic emergence of a new A. rugioperculatussuggest for the gradient outbreak of the pest, in tune with the weather change phenomena experienced in 2016 in South India. Under such situations, no insecticides should be applied to manage the pest. Introduction of parasitized pupae is a good strategy in the emerging pest inflicted zones for effective bio-suppression of whitefly.
Parasitism was relatively low in pesticide-sprayed gardens in Pollachi, Tamil Nadu. The parasitism percentage ranged from 25-30% indicating the upset in distribution of parasitoid due to indiscriminate use of pesticides especially those belonging to synthetic pyrethroid category.
1) Application of 1% starch solution on leaflets to flake out the sooty moulds.
2) Installation of yellow sticky traps on the palm trunk as well as in iterspaces to trap adult whiteflies.
3) Encourage build up of parasitoids (Encarsia sp.) and re-introduce parasitized pupae to emerging zones of whitefly outbreak.
4) In severe case, spray neem oil 0.5% and no insecticide is recommended.
Being a new whitefly species, the spread will be quite rampant initially. Since the natural enemy build up has been initiated, it may not go beyond action threshold as expected. Therefore awareness campaigns need to be followed in all epidemic zones to sensitize the farming community about the whitefly pest and conserve the natural enemies to ward off the pest. Sensitization programme focusing on the natural build of the parasitoid, Encarsia sp. in spiralling whitefly endemic areas should be projected as a classical example of bio-control strategy in sustainable pest management in coconut system. Our approach should, therefore, be to encourage the niche survival of Encarsia sp. for affective bio-suppression of A. rugioperculatus.
ICAR-CPCRI has already sensitized State Department of Agriculture Development and Farmer’s welfare in different districts of Pathanamthitta, Kottayam, Kannur and Palakkad. A sensitization programme alerting the outbreak of RSW was organized by the State Department and was held at Kozhinjampara, Palakkad on 23-11-2016 under the leadership of Hon’ble Member of Legislative Assembly Sri. Krishnankutty. Farmers from Pollachi, Tamil Nadu were thoroughly exposed on the parasitic bio-suppression of A. rugioperculatus. during the ATMA exposure visit to the ICAR-CPCRI, Regional Station, Kayamkulam on December 26-27, 2016. Red alert message has been sent to all dailies on the conservatory approach of natural parasitoid, Encarsia sp to combatA. rugioperculatus. Dr. P. Chowdappa, Director, ICAR-CPCRI, has highlighted the potential invasive pests of coconut and the management strategies to tackle with greater emphasis on the A. rugioperculatus. ICAR-CPCRI has published a note n Kerala Karshakan and one paper is accepted in Indian Coconut Journal.