Entomon 1989 Vol. 14 No. I & 2 pp. 79 to 80

RESIDUAL TOXICITY OF CERTAIN INSECTICIDES TO LEAF GALL THR[PS (LIOTHRIPS KARNYI BAGNALL)
ON BLACK PEPPER'

S. DEVASAHAYAM
National Research Centre for Spices, Marikunnu, Calicut, Kerala, India 673012

(Received 31 March 1988)

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Nine insecticides were evaluated for their residual toxicity to leaf gall thrips (Liothrips karnyi Bangnall) infesting black pepper (Piper nigrran L.). Initial toxicity was highest in monocrotophos which caused 90 per cent mortality up to 14 days after treatment. Monocrotophos continued to cause 50 per cent mortality up to 28 days after treatment. Monocrotophos and malathion caused some mortality up to 42 days after treatment. Analysis of PT (Persistence X Toxicity) indices also indicated that residual toxicity was maximum in monocrotophos followed by malathion.
(Key words: black pepper, Piper nigrran L., leaf gall thrips, Lioihrips karnvi Bagnall, residual toxicity of insecticides)

INTRODUCTION

Leaf gall thrips (Liotitrips karn_ri Bagnall) are important pests of black pepper (Piper iiignu,, L.) in Kerala especially at higher altitudes. The pest infests the leaves and induces the formation of marginal leaf galls within which they live. The feeding activity of the pest also results in reduction in size, crinkling and malformation of the infested leaves. NAIR & CHRISTUDAS (1976) and VIVEKANANDAN et al. (1981) have evaluated a few insecticides against field populations of leaf gall thrips. However, no information is available on the residual toxicity of various insecticides against the pest. The results of such studies conducted with nine insecticides (four systemic and five contact insecticides) are reported here.

MATERIALS AND METHODS

The experiment was conducted at the National Research Centre for Spices, Calicut under green house conditions. Rooted cut

'Contribution No. 81 of National Research Centre for Spices, Calicut 673 012.

tings of black pepper (var. Panniyur-l) raised in polythene bags were sprayed. with commercial formulations of the test insecticides so as to give a uniform and thorough coverage of the foliage. The insecticides tested included, dintethoate, formothion, monocrotophos, phosphamidon, dichlorvos, endosulfan, methyl parathion, quinalphos (0.05%) each and malathion (0. 1 %). Forty plants were utilised representing 10 treatments including a controland each treatment was replicated four times. A single leaf was clipped from each plant at 1, 3, 7, 14, 21, 28. 35, 42 and 49 days after treatment and placed. in glass vials of 14 x 2.5 cm size, the mouth of which was covered with a muslin cloth. A piece of cotton wool soaked in water was also placed in the vial to prevent dessication of the leaves. Ten adult leaf gall thrips collected from the field were then introduced into each vial and their mortality was recorded after 24 hours. The corrected percentage of mortality under various treat ments was calculated using the Abbott's formula (ABBOTT, 1925). The PT (Persistence X Toxicity) values were also calculated based