Derek Russell

Mitochondrial DNA analysis of field populations of Helicoverpa armigera (Lepidoptera: Noctuidae) and of its relationship to H. zea

BackgroundHelicoverpa armigera and H. zea are amongst the most significant polyphagous pest lepidopteran species in the Old and New Worlds respectively. Separation of H. armigera and H. zea is difficult and is usually only achieved through morphological differences in the genitalia. They are capable of interbreeding to produce fertile offspring. The single species status of H. armigera has been doubted, due to its wide distribution and plant host range across the Old World. This study explores the global genetic diversity of H. armigera and its evolutionary relationship to H zea.ResultsWe obtained partial (511 bp) mitochondrial DNA (mtDNA) Cytochrome Oxidase-I (COI) sequences for 249 individuals of H. armigera sampled from Australia, Burkina Faso, Uganda, China, India and Pakistan which were associated with various host plants. Single nucleotide polymorphisms (SNPs) within the partial COI gene differentiated H. armigera populations into 33 mtDNA haplotypes. Shared haplotypes between continents, low F-statistic values and low nucleotide diversity between countries (0.0017 – 0.0038) suggests high mobility in this pest. Phylogenetic analysis of four major Helicoverpa pest species indicates that H. punctigera is basal to H. assulta, which is in turn basal to H. armigera and H. zea. Samples from North and South America suggest that H. zea is also a single species across its distribution. Our data reveal short genetic distances between H. armigera and H. zea which seem to have been established via a founder event from H. armigera stock at around 1.5 million years ago.ConclusionOur mitochondrial DNA sequence data supports the single species status of H. armigera across Africa, Asia and Australia. The evidence for inter-continental gene flow observed in this study is consistent with published evidence of the capacity of this species to migrate over long distances. The finding of high genetic similarity between Old World H. armigera and New World H. zea emphasises the need to consider work on both pests when building pest management strategies for either.

Sustainable Pest Management for Cotton Production: A Review

Cotton cultivation, often highlighted for its excessive consumption of plant protection products, is taken as a model to illustrate the development of the ideas and practices of crop protection over the last 50 years. Cotton is grown in 69 countries on 30–35 million hectares and the production exceeded 20 million tones of lint in recent years. Despite the continual improvement in the performance of chemical control strategies, harvest losses remain very high, of about 30%. The largest consumer of pesticides in the world, the cotton production system has the advantage of having been an experimental model for many crop protection programmes under various agronomic conditions and in the presence of diverse pest complexes. Without attempting an exhaustive bibliography, this review explores how and why the ideas underlying crop protection have significantly evolved since the advent of synthetic pesticides. After a spectacular demonstration of yield growth through the application of chemical control, cotton production was rapidly confronted by the secondary effects of this control. These included the appearance of evolved insecticide resistance and the appearance of new damage caused by pests considered up to then as of only secondary importance. In extreme cases, the economic viability of the production systems themselves have been compromised following increases in the application rate and frequency of insecticidal treatments. In general, harvest losses have remained high despite the constantly improving technical performance of pest control chemicals. Two models of the future of crop protection can be drawn: total pest management which involves the eradication of pests, and integrated pest management (IPM), which aims at the management of pest populations below economic thresholds by a mixture of chemical control and a suite of alternative control measures. The first method, total pest management is limited in agricultural systems to particular cases in which the pest in question has no significant alternate hosts in the vicinity of the crop system. On the other hand, the application of IPM is constrained both by the difficulties in exploiting the concept of an ‘intervention threshold’ and by the limitations of many of the specific non-chemical techniques proposed, but does have the advantage of taking into consideration the full pest complex in a cropping system. In practice, it has been a calendar schedule, largely of insecticidal treatments, established on the basis of earlier local observations which has been most widely adopted by growers. This strategy has produced significant improvements in production in the cotton producing countries of francophone Africa and elsewhere. This has led to area-wide integrated pest management which takes into account the potential for natural factors to regulate populations in a specific region. In cotton production, biological control by introduction and acclimation of beneficial arthropods has not been notably successful because of the difficulty of developing a suite of beneficial organisms capable of responding effectively to the diversity of pests in the system, the annual nature of the crop, and the disrupting effects of chemical control measures directed against the remaining pests. Only inundative biological control has had significant success and then in particular cases where the pressure of chemical insecticides has been reduced. More benefit is to be obtained from the active conservation of the indigenous fauna of beneficial organisms. In spite of an increased general environmental awareness, in practice it has been the growth of evolved resistance to pesticides which has had the dominant role in constraining the growers to a more rational use of control strategies. These can be illustrated by the development of window strategies for control measures across the growing season, initially in Australia. The reduction in chemical control treatments made possible by the efficacy of genetically modified cotton has shown the positive role that indigenous natural enemies can play. At the same time, however, there has been a growth in the importance of pest species which are unaffected by Bt toxins. For example, the sucking pests are progressively coming to displace the vegetative and fruit feeding caterpillars as key pests of Bt cotton. Taking into account the spatio-temporal dimension of natural population regulatory factors has led to changes in agricultural practices and production systems. In cotton, for example, production systems maintaining permanent ground cover, are having increasing success. Intercropping and trap cropping have been favourable to the maintenance of beneficial arthropod complexes and unfavourable to the growth of pest populations. This new design context for crop protection in general and for cotton in particular, in applying the principles of agroecology, moves towards the concept of a truly sustainable agriculture. This implies a change of strategy towards a total systems approach to sustainable pest management, characterised by a movement from a paradigm of pest control field-by-field, through farm-by-farm and agroecosystem-by-agroecosystem, to a landscape by landscape approach.

Molecular markers to discriminate among four pest species of Helicoverpa (Lepidoptera: Noctuidae)

The four significant pest species in the Helicoverpa genus (H. armigera, H. assulta, H. punctigera and H. zea) are morphologically similar and can only be reliably distinguished through dissection of adult genitalia. Two partial regions of the mitochondrial DNA (mtDNA), the cytochrome oxidase subunit I (COI) and the cytochrome b (Cyt b) genes were amplified by PCR and digested with restriction endonucleases. The restriction patterns, generated by the endonucleases BstZ17I and HphI, demonstrated reliable differentiation of the four Helicoverpa pest species. This technique is fast, reliable and effective at distinguishing specimens irrespective of their life stages and offers support to conventional taxonomic differentiation based on morphological characters.

Multiple Resistances Against Formulated Organophosphates, Pyrethroids, and Newer-Chemistry Insecticides in Populations of Helicoverpa armigera (Lepidoptera: Noctuidae) from Pakistan

ABSTRACT Field populations of Helicoverpa armigera Hübner from 15 localities across the Punjab, Pakistan, were assessed by the leaf dip method for resistance against formulated organophosphates, pyrethroids, and newer insecticide groups. Resistance levels in H. armigera have been incrementally increasing for organophosphate and pyrethroid insecticides after decades of use in Pakistan. Resistance ratios (RRs) documented for organophosphates were 24- to 116-fold for profenofos and 22- to 87-fold for chlorpyrifos. For pyrethroids, RRs were 3- to 69-fold for Cypermethrin and 3- to 27-fold for deltamethrin. Resistance levels against newer chemistries were 2- to 24-fold for chlorfenapyr, 1- to 22-fold for spinosad, 1- to 20-fold for indoxacarb, 1- to 18-fold for abamectin, and 1- to 16-fold for emamectin benzoate. Resistant populations of H. armigera were mainly in the southern part of the Punjab, Pakistan. The most resistant populations were collected from Pakpattan, Multan, and Muzzafargarh. Of the nine insecticides tested, LC50 and LC90 values were lower for newer insecticide groups; resistance levels were moderate to very high against organophosphates, very low to high against pyrethroids, and very low to low against the newerchemistry insecticides. These findings suggest that the newer-chemistry insecticides with different modes of action could be included in insecticide rotations or replace the older insecticides. Supplementing the use of synthetic insecticides with safer alternatives could help to successfully lower the farmers reliance on insecticides and the incidence of resistance due to repeated use of insecticides against major insect pests.

Changing Trends in Cotton Pest Management

The cotton crop sustains more insects than any other crop grown commercially world-wide. Any single insecticidal intervention to control a particular pest invariably sets up a chain reaction causing short-term imbalances in the ecosystem, mostly in favour of the pest in the long run. Thus over the years, insecticide use was establishing undesirable ecological and economic consequences for cotton cultivators and administrators in many countries. Individual insecticide molecules when first introduced have always been impressive in their rapid efficacy in controlling target insect pests. As long the target pests are effectively controlled with the pesticide, cultivators do not care for the naturally occurring predators and parasites in their ecosystems. Unfortunately almost all the insecticides have inadvertent adverse effects on naturally occurring beneficial insects. However, phytophagous target pests usually develop resistance much faster than entomophages, thereby causing pest populations to survive the pesticide, increase in numbers in the absence of natural control, and so generate outbreaks. The cotton crop has been subjected to more pesticide exposure than any other crop, in all cotton growing countries of the world. Intense insecticide use has resulted in insect resistance to insecticides, pesticide residues, and the resurgence of minor pests causing immense problems to cultivators. With the most reliable tools turning redundant, pest management experts started exploring the utility of naturally occurring pest control components as alternatives to replace the chemical insecticides. Thus, Integrated Pest Management (IPM) programs began to take shape as ‘intelligent selection and use of pest management tactics which results in favorable ecological, sociological and environmental consequences’ as defined by Rabb (1972). Insecticide Resistance Management (IRM) strategies have strengthened pest management systems by identifying appropriate insecticides, rates and timings so as to delay resistance, ensure effective control of target pests, and conserve naturally occurring biological control for enhanced sustainability of ecosystems. With the recent introduction of Bt-cotton, novel eco-friendly pesticides and IRM strategies, coupled with the trends in technology dissemination through area-wide farmer participatory approaches and farmer field schools, IPM programs all over the world have improved their sustainability and economic success.

Assessing the Susceptibility of Cruciferous Lepidoptera to Cry1Ba2 and Cry1Ca4 for Future Transgenic Cruciferous Vegetables

ARSTRACT Advances in transgenic plants expressing Bacillus thuringiensis (Bt) insecticidal gene (s) offer a promising alternative to traditional insecticides for control of lepidopteran pests on important cruciferous vegetable crops such as cabbage and cauliflower. A public-private partnership, the Collaboration on Insect Management for Brassicas in Asia and Africa (CIMBAA), was formed in 2005 with the goal of developing dual-gene Bt cauliflower and cabbage, initially for India, to replace the use of broad spectrum, traditional insecticides. As a first step in this effort, the major lepidopteran pests of cruciferous vegetable crops [Plutella xylostella (L.), Pieris rapae (L.), Pieris brassicae (L.), Crocidolomia binotalis (L.), Hellula undalis (F.), Diacrisia obliqua Walker, Spodoptera litura F., and Helicoverpa armigera (Hübner)] were collected over a large geographic area (India, Indonesia, Taiwan, China, Australia, and the United States) and tested against purified Cry1Ba2 and Cry1Ca4 toxins, the toxins proposed to be expressed in the CIMBAA plants. Our results demonstrate that Cry1Ba2 and Cry1Ca4 were effective against the primary target of the CIMBAA plants, P. xylostella, regardless of geographic location, and had LC50 values <1.3 ppm. Furthermore, one or both toxins were effective against the other major pest Lepidoptera, except for S. litura or H. armigera which were less susceptible. No cross-resistance has been found between Cry1Ba2 and Cry1Ca4, suggesting cry1Ba2+cry1Ca4 cauliflower and cabbage could be an effective and sustainable tool to control, P. xylostella, the key lepidopteran pest on cruciferous vegetable crops, as well as most other Lepidoptera. As the CIMBAA plants are being developed, further tests are needed to determine whether they will express these proteins at sufficient levels to control all the Lepidoptera. Sustainable use of the dual-gene plants also is discussed.

OfftargetFinder: a web tool for species-specific RNAi design.

MOTIVATION RNA interference (RNAi) technology is being developed as a weapon for pest insect control. To maximize the specificity that such an approach affords we have developed a bioinformatic web tool that searches the ever-growing arthropod transcriptome databases so that pest-specific RNAi sequences can be identified. This will help technology developers finesse the design of RNAi sequences and suggests which non-target species should be assessed in the risk assessment process. AVAILABILITY AND IMPLEMENTATION http://rnai.specifly.org CONTACT crobin@unimelb.edu.au.

Promoting Integrated Pest Management for Cotton Smallholders—The Uganda Experience

Cotton production in Uganda which depends on smallholders, has fallen well below the levels of national production seen in the 1960s. Poor standards of crop management contribute to low profitability and control of insect pests is an important management component, with insecticides accounting for up to 50 % of input costs. An integrated pest management (IPM) system appropriate for smallholder adoption was developed and promoted as part of a larger program based on large numbers of on-farm demonstrations. The main insect pests in Eastern Uganda are the bollworms (Helicoverpa armigera, Pectinophora gossypiella and Earias insulana and E . biplaga) and Lygus bug (Lygus spp.) can cause leaf tattering and destruction of flowers. Later in the season, stainer bugs (Dysdercus spp.), can cause lint staining and secondary boll rots. The two key IPM components were the use of soapy water to control early season aphids, so as to delay the first use of a toxic insecticide and a ‘user friendly’ pest scouting method, to inform the farmer of the optimum time to spray and help in deciding what to spray. The use of a ‘peg-board’ as a scouting aid was adopted among cotton farmers in Uganda and spray schedules informed by scouting delivered better pest control and higher profits than fixed schedule spraying. Implementation of the IPM system did not necessarily result in decreased number of sprays compared to the nationally recommended fixed schedule of 4 sprays. In a season of low bollworm pressure, one less spray was required but in a season of higher pest pressure, one additional spray was required under the scouting-based IPM system. However, the timing and appropriateness of the intervention was greatly improved, with positive implications for crop protection and yields. The main lesson from the experience in Uganda was that pest scouting and IPM can be readily adopted by African smallholders, provided they have access to good quality inputs and sufficient technical support. The large number of on-farm demonstrations was also an important method of knowledge transfer.