Trends in Research on Arthropod Pests of Vegetables in Ethiopia

Abstract

Vegetables such as cabbage, pepper, onion, and tomato are widely cultivated and consumed in Ethiopia. They form an important part of the diet and play key roles in diversifying the economy of rural fanners and the agriculture sector in general. Several residents and invasive arthropod pests currently constitute the highest challenge in the production of vegetables in Ethiopia. Due to the absence of periodic surveys, the number of species associated with vegetables is not fully known. New introductions are usually recognized after heavy infestation occurred. A good example is the tomato leaf miner, Tula absoluta, believed to be introduced in 2012. Earlier published works show the occurrence of over 25,7,22, and 25 arthropod species associated with, cabbage, onion, pepper, and tomato, respectively. According to Horizon scanning tools of CABI, 300, 72, 316, and 251 species are mentioned as dangers to cabbage, onion, pepper and tomato, respectively, for Ethiopia. O f these 21, 11, 18, and 14, respectively are worked out to be quarantine pests for Ethiopia using EPPO global database, CABI distribution map, and literature search on published insect pests list of the four vegetable crops in Ethiopia. Several studies on ecology and management including cultural, biological, and chemical methods have been made on one or more key insect pests of the major vegetables produced. However, chemical control continues to be the most preferred and primary management tactic by producers. About three dozen of insecticides have been registered for the control of some key major arthropod pests on vegetables. However, a couple of insecticides appear to give good level of control. Misuse and abuses of insecticides have resulted in fast efficacy decline of insecticides. A good example is the diamide insecticide Coragen (Chlorantraniliprole) registered for the control of the tomato leaf miner (Tula absoluta). The level of tomato fruit infestation in fields treated with Coragen was about 5% compared to up to 100% in the untreated when it was registered in 2013. Currently, the level of Tuta control achieved with the use of Coragen is nearly nil in most areas of the Central Rift valley (CRV) region probably because of the development of resistance. Similar trends in efficacy decline of the formerly effective insecticides like lambda cyhalothrin has been observed on onion thrips in the CRV region probably because of resistance development and or a mixed infestation of Thrips tabaci and Frankliniella occidentalis. The nonchemical control options developed for the control of some arthropod pests have not been utilized by the vegetable producers for several reasons. The only exception is the implementation of classical bio-control of Diamondback moth, Plutella xylostella, using the larval parasitoid Diadegma semiclausum (Hymenoptera: Ichneumonidac) in the cabbagc production area of Kofele highland where pesticide use for pest control is minimal. Unavailability of the products in the market such as bio-pesticides and attractants can be mentioned as reasons for the non­ adoption of the non-chemical control methods by the vegetable growers. Efforts are currently underway to reassess the efficacy of the registered insecticides against key insect pests of major crops to develop a pesticide resistance management program in the CRV. Initiatives also exist in demonstrating rational use of effective insecticides along with some nonchemical control approaches on farmers' fields in the CRV. Responding to pesticide-related problems in vegetable production along with strengthening IPM deserves attention by all stakeholders. The paper also outlines future directions of vegetable pest management in Ethiopia.