The Role and Effectiveness of Refuge Crops in Bacillus Thuringiensis
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The Role and Effectiveness of Refuge Crops in Bacillus Thuringiensis Cotton Production, to Reduce Helicoverpa armigera and Helicoverpa punctigera Numbers for Resistance Management. William Tan SID: 308238826 AFNR Research Project B / Research Paper 2013 Number of words: 7933 Number of references: 38 Number of figures: 18 1 | P a g e Thesis Table of Contents 1. Abstract……………………………………………………………………………….4 2. Introduction……………………………………………………………………….….5 a. Pest…………………………………………………………………………….5 b. Integrated Pest Management………………………………………………..7 c. Bt Cotton…………………………………………………………………….10 d. Refuge………………………………………………………………………..11 3. Materials and Method………………………...…………………………………….16 a. Site Description……………………………………………………………...16 b. Visual counts/ Pupae dig method……………………………………...…...17 c. Experimental Design………………………………………………………..17 d. Statistical Analysis…………………………………………………………..19 4. Results……………………………………………………………………………….20 a. Attractiveness……………………………………………………………….20 b. Productivity…………………………………………………………………21 5. Discussion…………………………………………………………………………....26 6. Conclusion…………………………………………………………………………...30 7. References…………………………………………………………………………...31 2 | P a g e Thesis Publications by the Candidate Relevant to the Thesis Tan, W.N., Mansfield, S., Whitehouse, M.E.A., Cross, D. 2013. Corelating refuge attractiveness with productivity (abstract) In: Proc. Of the Association of Australian Cotton Scientists’ Inaugural Cotton Research Conference, 8-11 September 2013, Narrabri, NSW. Association of Australian Cotton Scientists, Narrabri, p.73. Industry Reports Tan, W. N. 2013. Correlating refuge attractiveness with productivity. Cotton Research Development Corporation Summer Scholarship Program Progress Report (10pp) Awards 2013 Winner of best student poster for “Correlating Refuge Attractiveness and Productivity” at the AACS Inaugural Australian Cotton Research Conference. 3 | P a g e Thesis 1. Abstract Bt cotton has been extremely effective at controlling moths of the genus Helicoverpa. In order to delay the development of resistance by Helicoverpa to the Bt toxins, moths emerging from Bt cotton carrying the recessive resistant gene need to mate with susceptible individuals who do not carry the resistant gene. Refuges are planted to produce these susceptible moths. As pigeon pea is regarded as twice as attractive and productive to Helicoverpa as cotton, growers only need plant half as much pigeon pea as cotton refuges. However, on commercial cotton farms where cotton and pigeon pea refuges don’t synchronize flowering, and experience differing amounts of care, is pigeon pea still advantageous? To see if pigeon pea refuges are twice as attractive and productive as cotton refuges, we correlated attractiveness, productivity and plant parameters within and between cotton and pigeon pea refuges grown on commercial farms. We used egg counts to quantify attractiveness, and pupae digs to quantify productivity. Overall, pigeon pea refuges in our sample were twice as attractive and productive as the cotton refuges, while the larvae developing in cotton tended to have a higher survival rate. The attractiveness of the pigeon pea was correlated with the proportion of the crop that was flowering as opposed to forming pods. Results indicate that the pigeon pea is most effective when the pods are flowering, and hence timing is important when planting as you want this to synchronise with the resistant moth emergence in Bt fields. Pigeon pea was only effective when it was looked after and able to reach its flowering potential. These results show the importance of insuring that pigeon pea flowers at the appropriate time to be an effective and attractive refuge. 4 | P a g e Thesis 2. Introduction The Pest Helicoverpa belongs to the family Noctuidae, and H. armigera and H. punctigera have the common names ‘cotton boll worm’ and ‘native budworm’ (Grundy. T 2012). These are common pests of cotton and do damage to all vegetative and reproductive parts of the plant during their caterpillar stage and at all instar levels. They are not host specific to cotton, as they are also pests of sunflower, lupins, linseed, tomatoes, beans, peas, lucerne, maize and tobacco (Jones D 2012). Helicoverpa spp. is so successful worldwide because of high fecundity, mobility, facultative diapause and polyphagy (Fitt, 1989). Lifecycle (Figure 1) At 25°C, Helicoverpa spp. eggs take 3-4 days to hatch. During this time eggs turn from white to brown, and close to hatching, the black head capsule of the larvae is visible through the eggshell. Larvae develop through five or six growth stages (instars) and become fully grown larvae in 2-3 weeks. With the inclusion of the time from moth emergence to fertile egg production of around 5 days, a generation is estimated to be completed in about 40 days during summer, however this may vary depending on day degrees and day length (Knight 2013). Four to five generations occur per growing season. Final instar larvae move to the soil to pupate, usually not far from the base of the plant where they completed development. These larvae dig a tunnel leading to a chamber in which they enter the pupae stage. In this stage they undergo metamorphosis and emerge as adults. The final larvae build an emergence tunnel from the pupae chamber to the soil surface (usually <10cm). During summer pupae maturation takes about 16 days. However, late in summer, as day length shortens and temperatures fall an increasing proportion of these pupae will enter diapause and will spend the winter as pupae. Cultivation of the soil to a depth of 10cm during winter 5 | P a g e Thesis destroys the emergence tunnels, directly kills many pupae and brings others to the soil surface where they are eaten by predators such as birds (Mares 2012). Figure 1. Lifecycle of a typical Helicoverpa spp. (Varela 2003) Damage and Economics H. armigera and H. punctigera are common pests of cotton, damaging all vegetative and reproductive parts of the plant. They are not host specific to cotton and feed upon other plants including sunflower, lupins, linseed, tomatoes, beans, peas, lucerne, maize and tobacco (Jones & Elliot 2012). These pests cause damage as larvae, and damage cotton bolls results from the feeding of later instar larvae. The larvae burrow into the immature fruit capsule and consume the white damp lint held in the fruiting body. These pests can cause either direct damage via consumption of cotton bolls, or indirect damage, when eating leaves and flowering parts by opening wounds for pathogens to enter, and reducing the quality of the cotton. A study was conducted on conventional cotton comparing the economic costs of Helicoverpa from 5 seasons leading up to 1996/1997 and the six years leading up to 6 | P a g e Thesis 2002/2003 (Fitt et al. 1994). The results were an averaged $325/ha of costs towards Helicoverpa control and an averaged $562/ha respectively and a combined cost of $282 million per annum on control and residual damage. This shows how much cost of sprays has risen over the years and the economic impact of Helicoverpa, Bt cotton however has since changed the cotton industry, making farming practices more environmentally friendly by reducing insecticidal sprays by up to 80% (Fitt et al. 2000). With the introduction of transgenic Bt cotton, the industry has been looking into long term sustainable farming practices as well as encouraging more environmentally friendly management of land. Therefore with the introduction of Bt cotton, a producer’s economic threshold has to be adjusted to account for new factors. One of these factors is the reduction of insecticide sprays, enabling farmers may to save money that would have been spent on sprays. However, growers now have to incorporate biological control and refuge management into their economical thresholds. Another factor is the cost of environmental contamination. Previously high levels of chemical waste built up when using conventional cotton due to sprays. Now there is a potential for Bt toxin to build up in the soil while growing the cotton (Helassa 2010). Along with this, habitat diversity becomes a large part of biological control, as attraction of beneficial insects to the farm will help with a lot of control over Helicoverpa. These include creating alternative prey sources for beneficials or increasing the local nectar sources via diversity of flora in the area (Fitt et al. 2000). Integrated Pest Management Management in Bt Management of Helicoverpa spp. is usually done within the IPM (Integrated Pest Management) framework. IPM involves incorporating chemical, with cultural and biological 7 | P a g e Thesis practices to control the population of pest insects. Biological methods in the cotton industry rely heavily on parasitoids to control numbers, as parasitoids which exist naturally in the field are mainly parasitic wasps, and flies, these groups will lay their eggs either externally or internally in the caterpillar, and from there the parasitoid larvae will feed once emerged. Chemical control almost no longer exists now that Bt cotton is around as none is usually needed, however management practices need to be put in place to counter resistance. Cultural control involves the physical change of the environment, including cultivation to destroy pupae (pupae busting). Biological Biological methods of pest management is defined as the control of a pest by the introduction of a natural enemy or predator (Gullen 2010). Cotton fields typically contain a rich diversity of insects, and up to 450 different species can be found. Most