PhD

A state wide survey was conducted in Kerala during 1988 with a view to ascertaining the distribution and severity of incidence of C. arecae and yellow leaf disease on arecanut. The pest enjoyed a state wide distribution while the disease was present only in 40 per cent of the locations covered in the survey. Based on the percentage of the infested palms and on adult popula tion of the insect, the southern zone was found as most affected and the nymphal population was more in the northern zone. Based on total population northern and southern zone came on par. The leaf injury caused by the bug was higher in the northern zone and other zones came on par and less effected. Thus on different criteria the severity of the pest infestation in different agroclimatic zone did not show consistency .Vadakkanchery and Palghat in the middle zone were identified for the first time as the only pest free locations in Kerala.
In southern zone, Pandianpara, Kattakkada and Ettiruthi had high pest incidence while at Theviyode, Vithura and palode the infestations were found comparatively lower. A consecutive monthly monitoring of the populations in five of the above locations during 1987-89 revealed that places found less affected in the single state wide survey were seen badly affected and vice versa in repeated assessment. In the problem zone Moncompu, Vytilla and Chengannur were much more affected than Karthikaplly, Kumarakom and Karunagapally. In the middle zone, Alwaye, Pattikkad and Peechy were more affected than Vadakkanchery, Palghat and Mukundapuram. In the hill zone Peringamala, Vythiri and Ernadu had much higher population than Vaduvanchal and Kottapady. In northern zone Calicut, Taliparamba, Madhur and Koipady were more infested than Kumbla, Tellichery and Koothuparamba. Since repeated survey over two years reversed the relative position of the locations based on single survey, the latter did not appear conclusive thus suggesting the need for resorting to control measures throughout the state for tackling the pest problem.
A new spot of high incidence of yellow leaf disease in north Kerala was detected at Irrikkur near Cannanore. Incidence of C.arecae and yellow leaf disease did not show any association in different agroclimatic zones in Kerala or among different locations within each zone. Continuous monitoring of the population over 24months revealed that the occurrence of immature stages and adults overlapped, indicating continuous breeding of the pest. Period of high/low incidence of pest could not be identified consistently. The occurrence of the symptoms of yellow leaf disease did not coincide with the levels of fluctuating pest population. Maximum temperature and minimum relative humidity showed negative and positive correlation with the pest population respectively.
C.arecae fed and multiplied on its alternate hosts A. triandra, C. lutescens and pinanga sp.as favourable as on A catechu. E.guineensis also was found a suitable host since the immature and adult stages of the pest on the host showed more favourable attributes when compared to those on A. catechu.
The feeding behavior of the insect relating to the ‘plant surface exploration ‘,’exploratory probes ‘ and ‘imbibing food ‘ agreed with the behavior of other ‘Cimico-morphs’ described by earlier workers.
The feeding suppressed the emergence of spindle leaf partly or fully depending on the period of the damage. Total suppression of spindle leaf emergence even choked further growth of the palm. Injury caused by oviposition was observed in detail for the first time .Characteristic ‘pot marks’ made on the rachis of the leaf and the internal damage also were noted in detail for the first time.
Histological observations of the leaf along the feeding marks showed that the bug resorted to ‘lacerate and flush’ feeding .Formation of water soaked areas soon after stylet insertion , continuance of plasmolysis after the removal of the insect from the feeding spot and later discolourations and collapse of cells indicated that the action of the saliva would have caused the injury . Histochemical studies of the injured leaf lamina showed accumulation of proteins and lipids in the portion . The above host reactions were detected for the first time .
A new technique of warding off C. arecae from the crown of areca palms by keeping phorate /carbofuran granules in perforated polythene sachets , at the leaf axil, was developed and standardized . The technique was evaluated at field level in comparison with the recommended methods of spraying insecticides on the crown or keeping granules directly in leaf axils. On the basis of cost and bioefficacy, the new technique was found far superior to the recommended practices.
Salivary glands of C.arecae , exposed on yellow leaf disease affected palms for 20 to 33 days (ensuring acquisi-tion and incubation periods for MLO), were excised , processed , stained and examined under electron microscope for locating mycoplasma like organisms in the acini of the anterior, posterior and lateral lobes, if any . The haemolymph drawn from such insects also was examined under electron microscope . MLOs were absent in all the preparations. This finding in conjunction with the absence of correlations between the pest population and disease incidence ruled out the possibility of the insect being a vector of the disease.