SECTION 1 : INTRODUCTORY. Chapter 1 Introduction. Pest status and economic damage

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1 SECTION 1 : INTRODUCTORY Chapter 1 Introduction Cotton production systems The cotton pest situation Cotton bollworm (Helicoverpa armigera) Pest status and economic damage

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5 COTTON BOLLWORM CONTROL species, with pink bollworm (Pectinophora gossypiella), spiny and spotted bollworms (Earias species) and the leaffeeding Spodoptera species also very significant. In subsaharan Africa red bollworm (Diparopsis sp) plays a significant role. The leafrollers Sylepta derogata (F) and Anomis flava (F) are also important is some areas. In the New World two other moths closely related to the cotton bollworm predominates the cotton ear worm (Helicoverpa zea) and the tobacco budworm (Heliothis virescens). In South America caterpillars of Alabama argillacea and Bucculatrix thurburiella are also important. Various weevil species, particularly of the genus Anthonomus are major problems, most especially in the New World where Anthonomus grandis, the boll weevil has been spreading aggressively though the South American cotton regions. True bugs (Lygus sp and other mirids and pentatomid bugs) are significant boll piercers and seed feeders in some parts of the world. Cotton stainers (particularly Dysdercus sp) are a problem in Africa and Asia. These, with aphids (esp. Aphis gossypii Glover), jassids (Amrasca and Jacobiella sps), thrips (Thrips tabaci or Franklinella spp) and spider mites make up the majority of the pest pressure in most areas. Whitefly (Bemisia tabaci Gennadius) have been an increasing problem, especially in heavily insecticide-using countries. The intractability of whitefly in particular has helped to promote the uptake of integrated pest management (IPM) practices in many areas. The major pests and the measures taken against them (including insecticidal and noninsecticidal components) are given for all the major cotton producing countries in ICAC (2005). Insecticides worth US $ 1.7 billion are used annually in cotton all over the world (Fig 1.3) although this figure may be expected to reduce with the spread of Bt cotton. This figure excludes the cost of carrying out the application, which can be significant as the average number of sprays usually ranges from 2 to 12 in most countries, with an average of approximately 5.5 sprays per season on the 33.5 million hectares of cotton. In some countries, such as Pakistan, cotton insecticide use can be over 80% of total national use for all purposes. Costs can be extremely high; annual insect control costs in Australian cotton averaged $US278/ha (Fitt 1994). Sixty percent of 6 CHAPTER 1: INTRODUCTION cotton insecticide use occurs in the developing countries of Africa and Asia and its use is often inappropriate, rather than based on rational and carefully considered criteria. Improving the utilization of this enormous investment is therefore very well worthwhile. The cotton bollworm The cotton bollworm, (Helicoverpa armigera) is the single most important member of the cotton bollworm complex. In India alone, until the advent of Bt cotton, over half the insecticide applications on cotton were directed against this one species. A tremendous amount of research has taken place into the biology and control of this pest. Figure 1.5. Host range of Helicoverpa armigera The most recent summary of the status of that work was presented in a workshop held at the International Centre for Research in the Semi Arid Tropics (ICRISAT) in India in The resulting publication 'Heliothis/Helicoverpa Management Emerging Trends and Strategies for Future Research' (Sharma 2005) is an invaluable resource, which has been drawn on extensively in the following introductory sections. Pest status and economic damage This species is known over most of the old world as the 'cotton bollworm' or sometimes 'African bollworm' in 7

6 COTTON BOLLWORM CONTROL Africa and 'legume pod borer' or 'gram pod borer' in India where it has a long history of economic damage on chickpea, pigeonpea etc. Although frequently called American bollworm in north Asia, it has no connection with the Americas other than the fact that it became an increasingly important pest of a range of Asian crops after the introduction and widespread cultivation of American th cotton (Gossypium hirsutum) early in the 20 Century. Because there is no universally used English name for this species, we are using the latin name, Helicoverpa armigera, in this book to avoid any confusion with other cotton bollworms. Its distribution includes most of Asia, as far north as Uzbekistan, most of Africa, Australasia and the southern Mediterranean region, 29 cotton producing countries in all (Figure 1.6). It is recorded from 182 plant species including cotton, chickpea, pigeon pea, peas, cowpea, sunflower, sorghum, groundnut, field beans, tomato, tobacco, maize (Gowda 2005) in addition to wheat, okra, castor and a wide range of field vegetables. Accurate figures for of global loss are not possible, but Sharma (2001) estimated losses of over $US900 million in chickpea and pigeon pea, with over $300 million loss in those crops in India alone (Reed and Latif 1990). Mean avoidable pigeonpea crop losses in India in 10 years of trials to 1992 were 34% and in E.Africa c.50% (Hillocks et al. 2000). In Australia Fitt (1994) estimated the cotton crop loss in Queensland at 7.7% despite the expenditure of $US4.2 CHAPTER 1: INTRODUCTION million for its control. Further references to losses in a range of African crops can be found in Youm et al. (2005). Sharma (2001) estimated total global crop losses to this pest at around $US5 billion globally, in addition to the c. $1 billion spent on insecticides for its control. Biology of Cotton bollworm Many workers have studied aspects of the biology of this species. The summary given here is largely drawn from the excellent review by King (1994) except where indicated. Fig.1.7 shows the developmental stages of the insect. Moths are generally active after dusk, particularly in the early part of the night, feeding on nectar or other food sources, with females active rather earlier than males. Egg laying starts sometime after dusk and is generally complete by midnight. In the field, cotton bollworm females lay between 100 and 1,000 eggs depending on the nutritive condition of the adult and the temperature, humidity and time of year. Oviposition starts on the fourth or fifth night after female emergence from the pupa. Egg numbers peak between day six and day nine after emergence. Where amino acids, as well as sugars, are available to females, longevity and fecundity is higher. Where host flowers are available, females prefer to lay close to them. In cotton most of the eggs are in the upper part of the plant canopy, particularly the upper surfaces of growing points and squares, with a preference for hairy over smooth plant surfaces. Figure Developmental stages of H. armigera Figure1. 6. Distribution of cotton bollworm - H. armigera 8 Cotton bollworm will lay eggs on an enormous variety of host plants but the criteria for selection of these plants is not well understood. There is some tendency for females to prefer to lay eggs on the same plant species on which they themselves were raised and there is some evidence of 9

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