Investigation of the malpractices of pesticide application on the population density of Spodoptera litura (Fabricius) and Cassida circumdata (Herst) in Alternanthera sessilis (L)

Abstract

Alternanthera sessilis is highly nutritious cheep food item, among the people in Sri Lanka. This is consumed as a raw food or partially cooked meal. Spodoptera litura (Fabricius) and Cassida circumdata (Herst) are the major pest species found in Alternanthera sessilis. Farmers use Trebone (Etofenprox) to control these pests by applying excess amount of pesticides, neglecting the recommendations of Department of Agriculture. Therefore, the effect of excess amounts of Trebone (Etofenprox) on the management of population density of S. litura (Fabricius) and C. circumdata (Herst) was investigated. Four plots of A. sessilis were treated with the amount of Trebone used by farmers (Treatment 1) and another four plots were not treated with the recommended dosage of Trebone (Treatment 2). Control plots were not treated with the pesticides. Percentage leaf damage and the pest density in two different treatments and control were estimated in two day intervals during one harvesting cycle. Frequency of spraying of pesticides, and the quantity of pesticides needed for framers method and recommended method was estimated. The percentage leaf area damage by S. litura (Fabricius) and C. circumdata (Herst) indicated significant differences between'two treatments as well with control (P < 0.05). Pest density of these two pests was also significantly different (P < 0.05) between the two treatments as well as with control. The percentage damage indicated by S. litura (Fabricius) is 21%, 332%, 47% in farmers method; recommended and control respectively. In C. circumdata (Herst) it was 17%, 36%, 47% in fanners method, recommended and control respectively. This reveals that the damage in recommended methods in still higher (about 33%), and that could be indicating of development of resistantance to the said dosage. Therefore farmers are using twice the amount of the pesticides than recommended. It was revealed that the farmers are harvesting A. sessilis two days after application of pesticides and sell them in common market neglecting the post harvesting period. This could be leading to serious health hazards in consumers and various problems in environment as well.