Genetically modified insect resistance in cotton: some farm level economic impacts in India

The paper explores the impact of insect-resistant Bacillus thuringiensis (Bt) cotton on costs and returns over the first two seasons of its commercial release in three sub-regions of Maharashtra State, India. It is the first such research conducted in India based on farmers' own practices rather than trial plots. Data were collected for a total of 7793 cotton plots in 2002 and 1577 plots in 2003. Results suggest that while the cost of cotton seed was much higher for farmers growing Bt cotton relative to those growing non-Bt cotton, the costs of bollworm spray were much lower. While Bt plots had greater costs (seed plus insecticide) than non-Bt plots, the yields and revenue from Bt plots were much higher than those of non-Bt plots (some 39% and 63% higher in 2002 and 2003, respectively). Overall, the gross margins of Bt plots were some 43% (2002) and 73% (2003) higher than those of non-Bt plots, although there was some variation between the three sub-regions of the state. The results suggest that Bt cotton has provided substantial benefits for farmers in India over the 2 years, but there are questions as to whether these benefits are sustainable. (c) 2004 Elsevier Ltd. All rights reserved.

Influence of socio-economic and cultural factors in rice varietal diversity management on-farm in Nepal

A questionnaire survey of 408 households explored the role of socio-economic and cultural factors in rice (Oryza sativa L.) varietal diversity management on-farm in two contrasting eco-sites in Nepal. Multiple regression outputs suggest that number of parcels of land, livestock number, number of rice ecosystems, agro-ecology (altitude), and use of chemical fertilizer have a significant positive influence on landrace diversity on-farm, while membership in farmers' groups linked to extension services has significant but negative influence on landrace diversity. Factors with significant positive influence on diversity of modern varieties on-farm were number of parcels of land and of rice ecosystems, access to irrigation, membership in farmers' groups, and use of insecticide. Within communities, resource-endowed households maintain significantly higher varietal diversity on-farm than resource-poor households and play a significant role in conserving landraces that are vulnerable to genetic erosion and those with socio-cultural and market-preferred traits. Resource-poor households also contribute to local diversity conservation but at lower richness and area coverage levels than resource-endowed households. Households where a female had assumed the role of head of household due to death or migrant work of her husband had less diversity due to lower labor availability. Landraces with socio-cultural and market-preferred traits are few in number but have potential to be conserved on-farm.

Differential susceptibilities of peach-potato aphid, Myzus persicae (Homoptera: Aphididae) and its parasitoid, Aphidius matricariae (Hymenoptera: Aphidiidae) to foliar insecticides on partially resistant and susceptible potato cultivars

In a field experiment the effects of Sumicidin (super) 5EC (fenitrothion), Metasystox EC25 (oxydemeton-methyl) and Tamaron SL600 (methamidophos), applied at different dosages, were evaluated against peach-potato aphid, Myzus persicae (Sulzer) and its parasitoid Aphidius matricariae Haliday on Cardinal and Desiree (respectively partially resistant and susceptible potato cultivars to M. persicae). Sumicidin (super) 5EC was found about 30% more effective in reducing aphid populations than the other insecticides tested. The highest doses of each insecticide caused maximum aphid mortality; in general aphid mortality appeared dose dependent. Almost all the higher and lower doses of the tested insecticides were about 19% more effective on Cardinal than on Desiree. The most significant result was the synergistic interaction at the lower doses with plant resistance, so that the same level of control was recorded with second highest dose on Cardinal as with the highest dose on Desiree. Also the same control level was achieved at the lowest dosage rate on Cardinal compared with the next higher dose on the Desiree. Sumicidin (super) 5EC was found least toxic to the parasitoid, A. matricariae in terms of percent parasitism, emergence of parasitoids and number of mature eggs in the emerging female parasitoids; increase of about 22, 67 and 47% respectively were found in parasitoid performance with Tamaron SL600 which was found comparatively highly toxic. The highest doses of all insecticides were found clearly toxic to the parasitoid. In general, effects on the parasitoid were dose dependent. Maximum yield was obtained from the second highest dose of Sumicidin (super) 5EC.

Selective toxicity of different granular insecticides to the peach-potato aphid, Myzus persicae (Homoptera: Aphididae) and its parasitoid, Aphidius matricariae (Hymenoptera: Aphidiidae) in two differentially resistant potato cultivars

Field studies were conducted in Pakistan to examine the effects and the interaction of two differentially resistant potato cultivars i.e. Cardinal and Desiree (one partially resistant and one susceptible to Myzus persicae (Sulzer), respectively) with different dosage rates of granular insecticides, at different time intervals after application in relation to percent kill of M. persicae and effects on the parasitoid Aphidius matricariae Haliday (i.e. the third trophic level) within the aphid mummies, percent parasitism and Thimet 10G (phorate) was found about 30% more effective in reducing aphid population than the Furadan 3G (carbofuran). The highest doses of each insecticide caused maximum aphid mortality, in general aphid mortality appeared dose dependent. Mostly all the higher and lower doses of the tested insecticides were about 10% more effective on Cardinal than on Desiree. The most significant result was the synergistic interaction at the lower doses with plant resistance, so that the same level of control was recorded with the second highest dose on Cardinal as with the highest dose on Desiree. Also the same level of control was observed at the lowest dose on Cardinal as with the second last lowest dose on Desiree. Furadan 3G was found least toxic to the A. matricariae in terms of percent parasitism, emergence of parasitoids and number of mature eggs in the emerging females. Furadan 3G gave 13, 15 and 6% higher figures, respectively from the parasitoid characteristics than Thimet 10G. The highest doses of both insecticides were clearly toxic to the parasitoid. In general, the effects on the parasitoid were dose dependent. The second highest dose of Thimet 10G, gave the maximum yield

Output risk aspects of genetically modified crop technology in South Africa

Technology involving genetic modification of crops has the potential to make a contribution to rural poverty reduction in many developing countries. Thus far, insecticide-producing 'Bt' varieties of cotton have been the main GM crops under cultivation in developing nations. Several studies have evaluated the farm-level performance of Bt varieties in comparison to conventional ones by estimating production technology, and have mostly found Bt technology to be very successful in raising output and/or reducing insecticide input. However, the production risk properties of this technology have not been studied, although they are likely to be important to risk-averse smallholders. This study investigates the output risk aspects of Bt technology using a three-year farm-level dataset on smallholder cotton production in Makhathini flats, Kwa-Zulu Natal, South Africa. Stochastic dominance and stochastic production function estimation methods are used to examine the risk properties of the two technologies. Results indicate that Bt technology increases output risk by being most effective when crop growth conditions are good, but being less effective when conditions are less favourable. However, in spite of its risk increasing effect, the mean output performance of Bt cotton is good enough to make it preferable to conventional technology even for risk-averse smallholders.

Molecular comparisons of the Culex pipiens (L.) complex esterase gene amplicons

The amplification of carboxylesterase genes is a mechanism of organophosphate resistance in Culex mosquitoes. Amplified carboxylesterase genes from an insecticide resistant Culex pipiens strain collected in Cyprus were analysed and compared to other Culex amplified carboxylesterase alleles. A 12 kb section of genomic DNA containing two gene loci coding for carboxylesterase alleles A5 and B5 was cloned and sequenced. A comparison between this amplicon and one from a strain with co-amplified carboxylesterase alleles A2 and B2 revealed a number of differences. The intergenic spacer was 3.7 kb in length in the A5-B5 amplicon (2.7 kb in A2-B2) and contained putative Juan and transposable elements upstream of B5. A fragment of a gene with high homology to aldehyde oxidase was also present immediately downstream of A5. The comparison revealed no differences that would explain the successful spread of the A2-B2 amplicon worldwide whilst the A5-B5 amplicon is restricted to the Mediterranean. (C) 2004 Elsevier Ltd. All rights reserved.

Incorporation of in situ and biomarker assays in higher-tier assessment of the aquatic toxicity of insecticides

This study was designed to test the feasibility of integrating in situ, single species exposures and biomarker analysis into microcosm studies. Experimental ponds were dosed with pirimiphos methyl (PM) and lindane. C. riparius fourth instar larvae were deployed for 48 h on nine separate occasions during the study period before and after treatment. Surviving larvae were analysed for acetylcholinesterase activity (AChE). Survival and biomarker data were compared to chironomid assemblage analysis by monitoring insects emerging from the microcosms. Survival of chironomids within the in situ systems commenced on day + 16 after treatment with 31.6% and 53.3% survival in the lindane and PM treated ponds, respectively. In contrast, the first emergence from the microcosms occurred on days + 27, in respect to lindane, and + 59 for the PM treated ponds. Thus the in situ bioassay was able to demonstrate gradual reduction in toxicity within the sediment before this was evident from macroinvertebrate monitoring. Significant ACNE inhibition was only detected on exposure to PM. Levels decreased from 75% on day + 16 to 26% by day +29. The biomarker analysis confirmed that, by the end of the study, the insecticide was no longer exerting an effect. We discuss how the use of in situ bioassays could also aid comparison of microcosm studies by adding a standardized dimension. (C) 2003 Elsevier Ltd. All rights reserved.

Antixenosis to the peach/potato aphid, myzus persicae (SuIzer) in potato cultivars

Field studies were conducted to determine the antixenotic resistance against the peach-potato aphid, Myzus persicae (Sulzer) in different potato cultivars i.e. Cardinal, Ultimus and Desiree. These cultivars were studied in the paired tests as Cardinal vs. Desiree and Cardinal vs. Desiree for antixenosis (systemic insecticide-based test). In Desiree vs. Ultimus, no significant difference was found for the preference of M. persicae, while in case of Cardinal vs. Desiree, there was a significant preference for Desiree. Cardinal clearly showed antixenosis to M. persicae.

Plastic films for polytunnels can prolong the effective residual life of cypermethrin to over 6 months

Synthetic pyrethroid insecticides are degraded almost entirely by ultraviolet (UV)-catalysed oxidation. A bioassay using the beetle Tribolium confusum duVal caged on bandages soaked in 0.04% a.i. cypermethrin showed large differences in residual insecticide-life under three plastic films available for cladding polytunnels. Cypermethrin exposed to a UV film that transmitted 70% of UVB and 80% of UVA killed all beetles for 8 weeks, compared to only 3 weeks for cypermethrin exposed in a clear plastic envelope. Cypermethrin under a UV-absorbing film that reduced the transmission of UVB and UVA to 14% and 50%, respectively, gave a complete kill for 17 weeks. Reducing the transmission of UVB to virtually zero, and that of UVA to only 3%, using a UV-opaque film prolonged the effective life of the cypermethrin residue to 26 weeks, and some beetles were still killed for a further 11 weeks. Even after this time, beetles exposed to cypermethrin from the UV-opaque treatment were still affected by the insecticide, and only showed near-normal mobility after 24 months of pesticide exposure to the UV-opaque film. These results have implications for the recommended intervals between cypermethrin treatment and crop harvest, and on the time of introduction of insect-based biological control agents, when UV-opaque films are used in commercial horticulture.

Identifying and investigating pesticide application types to promote a more sustainable pesticide use: the case of smallholders in Boyacá, Colombia

The present paper investigates pesticide application types adopted by smallholder potato producers in the Department of Boyacá , Colombia. In this region, environmental, health and adverse economic effects due to pesticide mis- or over-use respectively have been observed. Firstly, pesticide application types were identified based on input-effectiveness. Secondly, their determinants of adoption were investigated. Finally suggestions were given to develop intervention options for transition towards a more sustainable pesticide use. Three application types were identified for fungicide and insecticide. The types differed in terms of input (intensity of pesticide application), effect (damage control), frequency of application, average quantity applied per application, chemical class, and productivity. Then, the determinants of different pesticide application types were investigated with a multinomial logistic regression approach and applying the integrative agent centred (IAC) framework. The area of the plot, attendance at training sessions and educational and income levels were among the most relevant determinants. The analysis suggested that better pesticide use could be fostered to reduce pesticide-related risks in the region. Intervention options were outlined, which may help in targeting this issue. They aim not only at educating farmers, but to change their social and institutional context, by involving other agents of the agricultural system (i.e. pesticide producers), facilitating new institutional settings (i.e. cooperatives) and targeting social dynamics (i.e. conformity to social norms).

Varietal effects of cowpea, Vigna unguiculata, on tolerance to malathion in Callosobruchus maculatus (Coleoptera: Bruchidae)

The impact of cowpea variety on the response of cowpea bruchid, Callosobruchus maculatus, to malathion was investigated. The interaction of six cowpea varieties (Adamawa Brown, Ife BPC, Ife Brown, Lilongwe, Ntcheu and NCRI-L25) with the geographical strains of C. maculatus (Brazil and Cameroon), temperature (23, 25, 27 C) and insecticide concentration were considered. Cowpea variety (V) had an unpredictable effect on C. maculatus response to malathion. Bruchid populations produced by Ife BPC were the most susceptible to malathion while those yielded by NCRI-L25 were the most tolerant. Regardless of the cowpea variety, the Brazil strain showed higher tolerance than the Cameroon strain. There was significant effect of temperature (T) and insecticide concentration (C) on malathion tolerance in both strains (S). Likewise, there was significant impact of all two-way interactions on cowpea bruchid tolerance except V x C. Significant three-way interactions on C. maculatus tolerance to malathion was only observed in S T V and S T C. The predictability of changing one of the factors on the susceptibility of C. maculatus to insecticide was very low. This study suggests a need to take the insecticide tolerance of insect populations produced by novel varieties into account during plant breeding in addition to factors such as yield and resistance to insect and disease attack.

Case study part 2: probabilistic modelling of long-term effects of pesticides on individual breeding success in birds and mammals

Abstract: Long-term exposure of skylarks to a fictitious insecticide and of wood mice to a fictitious fungicide were modelled probabilistically in a Monte Carlo simulation. Within the same simulation the consequences of exposure to pesticides on reproductive success were modelled using the toxicity-exposure-linking rules developed by R.S. Bennet et al. (2005) and the interspecies extrapolation factors suggested by R. Luttik et al.(2005). We built models to reflect a range of scenarios and as a result were able to show how exposure to pesticide might alter the number of individuals engaged in any given phase of the breeding cycle at any given time and predict the numbers of new adults at the season’s end.

Risk assessment of UK skylark populations using life-history and individual-based landscape models

Abstract: Following a workshop exercise, two models, an individual-based landscape model (IBLM) and a non-spatial life-history model were used to assess the impact of a fictitious insecticide on populations of skylarks in the UK. The chosen population endpoints were abundance, population growth rate, and the chances of population persistence. Both models used the same life-history descriptors and toxicity profiles as the basis for their parameter inputs. The models differed in that exposure was a pre-determined parameter in the life-history model, but an emergent property of the IBLM, and the IBLM required a landscape structure as an input. The model outputs were qualitatively similar between the two models. Under conditions dominated by winter wheat, both models predicted a population decline that was worsened by the use of the insecticide. Under broader habitat conditions, population declines were only predicted for the scenarios where the insecticide was added. Inputs to the models are very different, with the IBLM requiring a large volume of data in order to achieve the flexibility of being able to integrate a range of environmental and behavioural factors. The life-history model has very few explicit data inputs, but some of these relied on extensive prior modelling needing additional data as described in Roelofs et al.(2005, this volume). Both models have strengths and weaknesses; hence the ideal approach is that of combining the use of both simple and comprehensive modeling tools.

Antibiosis in wheat interacts with crowding stress to affect Metopolophiumdirhodum development and susceptibility to malathion

We used a laboratory study to compare the performance of rose-grain aphid, Metopolophium dirhodum(Walker)(Hemiptera:Aphididae),onthewheatcultivars‘Huntsman’(susceptible)and‘Rapier’ (partiallyresistant)inbothlowdensity(uncrowded)andhighdensity(crowded)coloniesandexamined the consequences for aphid susceptibility to malathion. Adult apterae that developed on Rapier wheat had their mean relative growth rate (MRGR) reduced by 6 and 9% under uncrowded and crowded conditions, respectively, whereas the crowding treatment reduced MRGR by 3%, but only in Rapier aphids. Rapier resistance also reduced adult dry weight by 13 and 14% under crowded and uncrowded conditions, respectively, whereas crowding reduced it by 34 and 35% in Rapier and Huntsman aphids, respectively. Development on Rapier substantially reduced the topical LC50 of malathion by 37.8 and 34.8% under crowded and uncrowded conditions, suggesting that plant antibiosis increased malathion susceptibility. By comparison, crowding only reduced the LC50 by 29.5 and 26.0% on Huntsman and Rapier. The LD50 data showed that reductions on aphid body size on Rapier and through crowding did not fully explain the differences in LC50. This was particularly in the values for crowded aphids that were actually 80% higher than for uncrowded ones. Thi sapparent tolerance of crowded aphids, however, may partly be due to loss of insecticide from small aphids at dosing. Evidence of synergy between plant resistance and insecticide susceptibility raisest he possibility of using reduced concentrations of pesticides to control aphids on resistant crop cultivars, with diminished impacts on non-target and beneficial species important in integrated pest management(IPM)program

The impact of secondary pests on Bacillus thuringiensis (Bt) crops

The intensification of agriculture and the development of synthetic insecticides enabled worldwide grain production to more than double in the last third of the 20th century. However, the heavy dependence and, in some cases, overuse of insecticides has been responsible for negative environmental and ecological impacts across the globe, such as a reduction in biodiversity, insect resistance to pesticides, negative effects on nontarget species (e.g. natural enemies) and the development of secondary pests. The use of recombinant DNA technology to develop genetically engineered (GE) insect resistant crops could mitigate many of the negative side effects of pesticides. One such genetic alteration enables crops to express toxic crystalline (Cry) proteins from the soil bacteria Bacillus thuringiensis (Bt). Despite the widespread adoption of Bt crops, there are still a range of unanswered questions concerning longer term agro-ecosystem interactions. For instance, insect species that are not susceptible to the expressed toxin can develop into secondary pests and cause significant damage to the crop. Here we review the main causes surrounding secondary pest dynamics in Bt crops and the impact of such outbreaks. Regardless of the causes, if non-susceptible secondary pest populations exceed economic thresholds, insecticide spraying could become the immediate solution at farmers’ disposal, and the sustainable use of this genetic modification technology may be in jeopardy. Based on the literature, recommendations for future research are outlined that will help to improve the knowledge of the possible longterm ecological trophic interactions of employing this technology.