Biology and Ecology of Apanteles Taragamae, a Larval Parasitoid of the Cowpea Pod Borer Maruca Vitrata
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General introduction Propositions 1. Like plant leaves, upon herbivory, flowers can produce volatile compounds that at- tract their natural enemies (This thesis). 2. When two solitary koinobiont parasitoids compete intrinsically for the same host, the early acting species does not always prevail (This thesis). 3. The response of a parasitoid to herbivore-induced plant volatiles is affected by multi- ple infestation. Research should thus include herbivory on different plant organs such as flowers and leaves (Based on Lucas-Barbosa et al. (2011) The effects of herbivore-induced plant volatiles on interactions between plants and flower-visiting insect. Phytochemistry DOI 10.1016/j.phytochem.2011.03.013). 4. Niche partitioning by two natural enemies optimizes control of their shared host/prey (Based on Amarasekare P (2000) Coexistence of competing parasitoids on a patchi- ly distributed host: Local vs spatial mechanisms. Ecology 81: 1286-1296). 5. Despite a long research history, the fitness benefit for plants producing herbivore- induced plant volatiles still needs to be determined (Based on Dicke M, Baldwin IT (2010) The evolutionary context for herbivore-induced plant volatiles: beyond the 'cry- for-help'. Trends in Plant Science 15: 167-175). 6. Thorough scientific writing including speculations is useful for determining future re- search themes (Based on Janzen HH (1996) Is the scientific paper obsolete? Cana- dian Journal of Soil Science 76: 447-451). 7. Open access is a communication tool that can increase the impact of scientific publi- cations. 8. The spongy texture is a highly desirable factor that determines the acceptability of cowpea snacks (cowpea fried paste locally called “Ata”) by consumers in Benin. Elie Ayitondji Dannon Biology and Ecology of Apanteles taragamae, a larval parasitoid of the cowpea pod borer Maruca vitrata Wageningen, 9 September 2011 Thesis committee Thesis supervisors Prof. dr. Marcel Dicke Professor of Entomology Wageningen University Prof. dr. ir. Arnold van Huis Personal chair at the Laboratory of Entomology Wageningen University Thesis co-supervisor Dr. Manuele Tamò Senior scientist at the International Institute of Tropical Agriculture, Benin Station, Cotonou, Benin Other members Prof. dr. ir. Rudy Rabbinge, Wageningen University Prof. dr. Bas J. Zwaan, Wageningen University Dr. ir. Wopke van der Werf, Wageningen University Dr. Arjen Biere, Netherlands Institute of Ecology, Wageningen This research was conducted under the auspices of the C.T. De Wit Graduate School of Plant Ecology & Resource Conservation (PE & RC) Biology and ecology of Apanteles taragamae, a larval parasitoid of the cowpea pod borer Maruca vitrata Elie Ayitondji Dannon Thesis submitted in fulfilment of the requirement for the degree of doctor at Wageningen University by the authority of the Rector Magnificus Prof. dr. M.J. Kropff, in the presence of the Thesis Committee appointed by the Academic Board to be defended in public on Friday 9 September 2011 at 11 a.m. in the Aula Elie Ayitondji Dannon Biology and ecology of Apanteles taragamae, a larval parasitoid of the cowpea pod borer Maruca vitrata, 188 pages Thesis, Wageningen University, Wageningen, NL (2011) With references, with summaries in Dutch and English ISBN 978-90-8585-948-2 General introduction Abstract Maruca vitrata Fabricius is a key insect pest of cowpea in West Africa. Larvae of this moth can cause up to 80% of yield losses. The first classical biological control programme against M. vitrata started in 2005 with the introduction of Apanteles taragamae Viereck from Taiwan into Benin by the International Institute of Tropical Agriculture (IITA), Benin station. Thorough knowledge on the bioecology of A. taragamae is a prerequisite for implementing such programme. The work described in the present thesis evaluated the biological potential of this larval parasitoid to fill to the gap of information on its biology and ecology. Special emphasis was put on the main factors that determine the effectiveness/ suitablility of biological control candidates, such as reproductive capacity, functional response, climatic adaptability, host foraging capacity, and non-target effects. The results revealed that two-day-old larvae were the most suitable host age, giving the highest percentage parasitism, lifetime fecundity and proportion of females. Larvae older than three days were not successfully parasitized. The percentage parasitism of two-day-old larvae was positively correlated with host density, indicating a good functional response of A. taragamae. Between 20 and 30 °C, the curve that described the relationship between the intrinsic rate of natural increase and the temperature for A. taragamae was above that of M. vitrata, suggesting that the parasitoid can faster build up its population than its host. The parasitoid showed its ability to use volatiles produced by cowpea flowers and host caterpillars when foraging. A host plant odour experience enhanced the capacity of the parasitoid to find uninfested flowers. The growth of non-parasitized or A. taragamae- parasitized larvae was slower and with reduced proportion of female wasps on some host plants compared to those reared on artificial diet. With regard to the non-target effects, the physiological host range and competitive ability of A. taragamae were assessed. None of the following lepidopteran species, Eldana saccharina Walker, Chilo partellus (Swinhoe), Mussidia nigrivenella Ragonot, Cryptophlebia leucotreta (Meyrick), Sylepta derogata Fabricius and Corcyra cephalonica Stainto, was successfully parasitized by A. taragamae, suggesting its specificity for M. vitrata in Benin. In no-choice competition with the egg-larval parasitoid Phanerotoma leucobasis, A. taragamae outcompeted the latter. All the above attributes suggest that A. taragamae should be a suitable biocontrol agent against M. vitrata. A cage release strategy involved the host plant Sesbania cannabina, which was artificially infested with M. vitrata, and inoculated with adults of A. taragamae. The parasitoid was released in seven selected locations in Benin but the first recovery studies did not yet yield any information on its establishment after the first generation. General introduction Table of content Abstract 5 Chapter 1 General introduction 9 Chapter 2 Functional response and life history parameters of Apanteles 37 taragamae, a larval parasitoid of Maruca vitrata Chapter 3 Effects of volatiles from Maruca vitrata larvae and caterpillar- 63 infested flowers of their host plant Vigna unguiculata on the foraging behaviour of the parasitoid Apanteles taragamae Chapter 4 Effect of Maruca vitrata (Lepidoptera: Crambidae) host plants 79 on the life history parameters of the parasitoid Apanteles taragamae (Hymenoptera: Braconidae) Chapter 5 Assessing non-target effects and host-feeding of the exotic parasitoid Apanteles taragamae, a potential biological 97 control agent of Maruca vitrata Chapter 6 General discussion 117 References 137 Summary 167 Samenvatting 171 Acknowledgements 177 Curriculum vitae 181 List of publications 183 Education statement 186 General introduction General introduction General introduction General introduction General General Introduction 01 Elie Ayitondji Dannon Abstract A classical biological control programme against the cowpea pod borer Maruca vitrata Fabricius started in 2005 at the International Institute of Tropical Agriculture (IITA), Be- nin station using the parasitoid wasp Apanteles taragamae Viereck. The pest status of M. vitrata has been well determined and various control methods have been developed. In this chapter, an overview of the different strategies to control the pod borer is given. The available information on the biology of A. taragamae is provided. The steps to im- plement a classical biological control programme are listed with particular attention for criteria commonly used to select or assess the efficiency of promising biological control agents. Finally, the overall and specific objectives of the present PhD thesis are pre- sented. 1 Introduction Cowpea, Vigna unguiculata (L.) Walp., is a leguminous staple crop widely cultivated in West Africa (Singh and van Emden, 1979; Zannou et al., 2004). As a major source of dietary proteins, it is expected to play a key role in human nutrition in this area of the world where few people have access to animal proteins (Phillips et al., 2003). Unfortunately, cowpea production is limited by several constraints. Of these, damage by insects remains the most important (Singh and van Emden, 1979; Egho, 2010). Several insect species have been reported attacking cowpea from the seedling stage to harvest and beyond during storage (Singh and van Emden, 1979; Jackai and Daoust, 1986; Egho, 2010). Maruca vitrata Fabricius (Lepidoptera: Crambidae) has been identified as one of the most destructive insect pests of cowpea (Taylor, 1978; Sharma, 1998). Its caterpillars heavily attack both flowers and pods inducing drastic yields losses (Taylor, 1978; Sharma, 1998). A number of integrated pest control methods, reviewed in this chapter, have been developed and tested for the control of this moth. In 2005, a classical biological control against the cowpea pod borer was initiated in Benin by introducing Apanteles taragamae Viereck (Hymenoptera: Braconidae). This parasitoid was originally collected from Taiwan (Asia), and was imported by the International Institute of Tropical Agriculture (IITA), Benin station following the different steps required when implementing a classical