Effects of Insecticide Treated Nets in the Management of Tomato Pests and Their Impact on Natural Enemies and Yield in Nairobi and Murang’a Counties
Juma, Victor Omondi
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Tomato is a popular vegetable in Kenya and is extensively grown by small-scale farmers. In spite of the economic benefits to the farmers, insect pests remain one of the most significant constraints to tomato production. Current insect pests control measures rely on pesticides despite the known hazards to human health and the environment. Repeated use of pesticides has also led to the development of resistance by pests. Therefore, it is important to evaluate other pest control strategies that are safe, effective and economically viable with the aim of minimizing the hazardous effects of insecticide residues. This study investigated the effectiveness of alpha-cypermethrin treated nets against tomato insect pests and its impact on yield and natural enemies of tomato pests. The study was conducted on station at the Kenya Agricultural and Livestock Research Organization (KALRO) experimental plots at Kabete and at the Horticultural Practical Training Centre (HPTC) in Thika over a six month period. A local variety of tomato, Riogrande®, was sown in the nursery and was transplanted on the fourth week after sowing. The insecticide treated nets with a mesh size of 0.9 mm and two non-treated nets with a mesh size of 0.9 mm and 0.4 mm respectively were used. The efficacy of the insecticide treated nets and non-treated nets (mesh size of 0.9 mm and 0.4 mm respectively) were evaluated over a six month period. Each treatment was replicated five times in a completely randomized block design. Assessing the abundance and diversity of insect pests and their natural enemies on tomatoes was carried out by collecting and counting their numbers weekly for every replicate. Ripe tomatoes were harvested twelve weeks after transplanting, sorted and classified into marketable and unmarketable fruits. The total number of marketable fruits and fruit weights were obtained. The data on the abundance and diversity of insect pests and their natural enemies was analyzed using the Shannon-Weaver diversity index and Berger–Parker dominance index, while Analysis of Variance (ANOVA) was performed on the yield data to test the differences in the number and weight of marketable fruits from the different treatments. The significant means were separated using the Tukey test (P<0.05). A total of seven pest species were identified infesting tomato seedlings (Aphis gossypii, Thrips tabaci, Bemisia tabaci, Agrotis spp., Schizonycha spp., Tetranychus spp. and Liriomyza trifolii) while nine pest species were identified infesting tomato plants during field production (Aphis gossypii, Thrips tabaci, Bemisia tabaci, Haltica pyritosa, Helicoverpa armigera, Tetranychus spp., Liriomyza trifolii, Systates spp. and Planococcus spp.). The 0.9 mm alpha-cypermethrin treated nets were effective in protecting tomato plants against Aphis gossypii, Bemisia tabaci, Planococcus spp. Liriomyza trifolii and Helicoverpa armigera. The numbers of Aphidius spp. and Chilomenes lunata were not significantly affected by the use of nets to protect tomatoes against pest attack. The mean marketable fruit weights were significantly higher for tomatoes harvested under treated nets compared with those harvested from non-protected plots at Kabete (P=0.0000533). Similarly, the mean number of marketable fruit weight were significantly higher under treated plots at Thika (P=0.002). The results of this study demonstrate the potential of using alpha-cypermethrin treated nets as a viable strategy in improving tomato yields through the reduction of pest numbers on the crop. The netting covers can be used as a component of integrated pest management in tomato production.
- MST-Zoological Sciences