The Behavior, Ecology and Control of Legume Flower Thrips, Megalurothrips Sjostedti (Trybom) In Cowpea Vigna Unguiculata (L.) Towards the Development of an Integrated Pest Management (IPM) Program in Kenya

Abstract

The overarching aim of this thesis is to investigate the behaviour and ecology of the legume flower thrips Megalurothrips sjostedti Trybom and develop alternative control method. Its specific goals are to: (1) assess pest problems and management methods practiced by grain legume producers, and identifying the cropping systems in the study areas in Kenya; (2) study the impact of climate change on the geographic distribution of legume flower thrips on cowpea growing regions of Sub Saharn African countries; (3) study the behavior and survivorship of the legume flower thrips to develop an alternative control techniques using different essential oils and their derivative compounds. In most cases, development of alternative pest management strategy poorly considers to assess the indigenous knowledge and the perception on pest management practice. All of that can give ideas to be studied, adapted and eventually served as the building blocks in IPM programmes. In order to estimate the status of grain legume pest management practice, a field survey was conducted through household interviews based on a semi-structured questionnaire in eastern Kenya districts in highly representative areas of the main grain legume producing zone. The main results were the following ones: farmers were able to identify key pests of grain legumes using pictorial guide namely the legume flower thrips Megalurothrips sjostedti, the cowpea aphid Aphis craccivora and the legume pod borer Maruca vitrata. In addition to that, the application of chemicals is the main control method practiced with an increasing concentration, chemical alternation, frequent application and mixing of chemicals to ensure pesticide effectiveness. This is an indicator of resistance development and less efficient way of managing pests. In addition, farmers mentioned the erratic rain as the main challenge together with damage caused by pests. These findings help filling the gap in the literature related to grain legume farmer’s knowledge on pest management and its practice. This can be a base line for developing alternative control strategy which can be helpful for an easy adaptation of newly developed strategies to the farming system and other realities. Since climate change is also one of the main problems mentioned by 93% of the respondents, an investigation on climate change effect on the geographic distribution of the legume flower thrips Megalurothrips sjostedti Trybom and its host crop in Africa has been conducted using 166 presence records of Megalurothrips sjostedti and 350 presence records of cowpea in order to model the climate change effects. MAXENT (Maximum entropy) modelling tool is used to predict the effects of climate change for the year 2055. AFRICLIM, a highresolution (up to 1 km) climate variable was used for projecting current and future potential distribution of this pest and its host in Africa. Rainfall and temperature are the influential environmental variables identified by a “jackknife” analysis. A study of the behavior and survivorship of legume flower thrips M. sjostedti was carried out with the intention of developing an alternative thrips controlling strategy; this study on the repellent effect of 24 plant extracts against legume flower thrips M. sjostedti was conducted using a visual cue-still air olfactometer in a fume hood. The results revealed that, among the tested 24 plant extracts, 7 showed a good repellency against M. sjostedti. The analysis based on this identification of the constituent compounds of the best repellent extracts was done using Gas Chromatography Mass Spectro photometer (GC-MS). Mono- and sesqui terpene hydrocarbon compounds from seven highly repellent extracts were identified. This has led to an investigation of the behavioural effects of the identified compounds on the second instars larvae and the adult female M. sjostedti. It has been studied the repellent, toxic and deterrent effect of 16 identified compounds against the adult female legume flower thrips M. sjostedti using different bioassay methodologies. The result revealed that the use of repellent extracts could be one of the useful in developing integrated pest management strategies for thrips on legume crops. In addition, the study of specific mode of actions of the identified compounds indicates that the tested compounds are not efficient as alternatives for insecticide application. Thus plant compounds could be used as a safe method of control in integrated pest management for the control of M. sjostedti and Thripidae family in combination with the current pest management strategies for grain legumes in Sub-Saharan Africa. However, the plant extracts and our results may be exploited by extending behavioural manipulation to plant compounds released by companion plants through volatile collection and test under laboratory and field condition.