Suppression of green peach aphid ( Myzus persicae) (Sulz.), citrus mealybug ( Planococcus citri) (Risso), and two spotted spider mite ( Tetranychus urticae) (Koch.) attacks on tomatoes and cucumbers by aqueous extracts from vermicomposts

Abstract

Vermicomposts are produced through interactions between earthworms and microorganisms in the breakdown of organic wastes. Aqueous extracts were prepared in commercial brewing equipment (Growing Solutions Inc.) from vermicomposts processed from pre-consumer food waste. The ratio of vermicompost to water was 1 to 5 v:v to produce a 20% aqueous solution. The effects of soil drenches at dilutions of 20%, 10%, and 5% vermicompost extracts, were compared with those of deionized water, in the suppression of green peach aphids, mealybugs, and two spotted spider mites attacking tomatoes and cucumbers, in greenhouse cage experiments. Tomatoes and cucumber seedlings were germinated and grown for four weeks in 25 cm diam. pots containing a soil-less growth medium Metro-Mix 360 and thinned to 4 plants per pot. They were then put under cages (40 cm × 40 cm × 40 cm) with a 0.2 mm mesh, with one pot containing 4 plants in each treatment cage. Plants were treated with soil drenches of 5%, 10%, or 20% vermicompost extracts or a deionized water control to field capacity, at germination and at weekly intervals thereafter. In each experiment, either 100 green peach aphids, mealybugs, or two spotted spider mites were released into each cage (25 pests per test plant), on leaves of the same plant species. Each vermicompost extract treatment and the deionized water control were replicated 4 times per pest cage experiment laid out in a randomized complete block design. Numbers of pests were counted and damage was rated (0, none to 5, total) on days 1, 3, 5, 7, 9, 11, 13 and 14 after pest release into the cages. All of the vermicompost extracts suppressed pest establishment on the plants, and their rates of reproduction for all three species of pests, significantly. They also caused some of the pests on the plants receiving the higher extract application rates to die after 14 days of treatment. The higher the rate of extract application the greater was the suppression of the pests. We concluded that the most likely cause for the unacceptability of the plants to pests and decreased reproduction and mortality, was the uptake of soluble phenolic materials from the vermicompost extracts into the plant tissues. These compounds are known to make plants unattractive to pests and to affect pest rates of reproduction and survival.