Managing infestation levels of major insect pests of garden eggs (Solanum integrifolium L.) with aqueousneem seed extracts

Abstract

Performance of Aqueous Neem Seed Extract (ANSE) at 75 g/L of water (22.5 kg/ha) was evaluated on Legon I variety of local garden egg in the field. The effect of ANSE was compared with a registered Bacillus thuringiensis Berl. (Biobit), a synthetic insecticide (Karate 2.5 EC) and an untreated control (water only). Karate and Biobit were applied at rate of 2.5 ml/L (800 ml/ha) and 0.8 g/L (0.24 kg/ha), respectively. The effect of each treatment on insect abundance, defoliators, shoot, bud and fruit borers were determined. Water traps were used to monitor the effect of the three products on the abundance of insect fauna associated with crop. Insects from seven major orders (Coleoptera, Lepidoptera, Odonata, Orthoptera, Diptera, Hemiptera and Hymenoptera) were found associated with the local garden egg. The major insect pests of the crop included the shoot and fruit borer, Leucinodes orbonalis (Guen.), which attacked the shoots and fruits, the bud borer (budworm) Scrobipalpa blapsigona (Meyrick), which oviposited into the buds and the feeding activities of the larvae, led to the abortion of buds, Pachnoda cordata (Drury) which scraped and chewed stem and shoot and defoliators comprising Acraea peneleos peneleos (Ward.), Acraea pharsalus pharsalus (Ward.), Zonocerus variegatus L., Eulioptera sp., Urentius hystericellus (Richter) and Phaneroptera nana (Stal.). Karate and ANSE significantly (p < 0.05) reduced population levels of some major pests such as P. cordata and Z. variegatus than Biobit. The mean number of L. orbonalis and S. blapsigona in the shoots and buds, respectively were significantly higher (p > 0.05) on plots treated with ANSE and Biobit than Karate. This suggests that neem seed extract and Biobit had little or no systemic action against shoot and bud borers of the crop in the field. Significantly fewer (p < 0.05) numbers of predators mainly ants and ladybird beetles were collected from plants treated with Karate compared to either ANSE- or Biobit- treated plots. This indicates that Karate had adverse effects on beneficial insects in the garden egg ecosystem. Karate and ANSE also significantly (p < 0.05) reduced percentage fruit damage, number of borers per fruit and the activities of leaf feeders. Although ANSE could not effectively control the shoot and bud borers as Karate, it performed better in reducing borer damage than either Biobit or control. With proper timing and innovative methods of application, aqueous neem seed extract can be used as alternative or supplement to synthetic insecticide for the management of vegetable pests of local garden eggs by resource poor farmers.


(Journal of the Ghana Science Association: 2001 3(3): 70-84)