Reductions in insecticide use from adoption of Bt cotton in South Africa: impacts on economic performance and toxic load to the environment

The study reported presents the findings relating to commercial growing of genetically-modified Bt cotton in South Africa by a large sample of smallholder farmers over three seasons (1998/99, 1999/2000, 2000/01) following adoption. The analysis presents constructs and compares groupwise differences for key variables in Bt v. non-Bt technology and uses regressions to further analyse the production and profit impacts of Bt adoption. Analysis of the distribution of benefits between farmers due to the technology is also presented. In parallel with these socio-economic measures, the toxic loads being presented to the environment following the introduction of Bt cotton are monitored in terms of insecticide active ingredient (ai) and the Biocide Index. The latter adjusts ai to allow for differing persistence and toxicity of insecticides. Results show substantial and significant financial benefits to smallholder cotton growers of adopting Bt cotton over three seasons in terms of increased yields, lower insecticide spray costs and higher gross margins. This includes one particularly wet, poor growing season. In addition, those with the smaller holdings appeared to benefit proportionately more from the technology (in terms of higher gross margins) than those with larger holdings. Analysis using the Gini-coefficient suggests that the Bt technology has helped to reduce inequality amongst smallholder cotton growers in Makhathini compared to what may have been the position if they had grown conventional cotton. However, while Bt growers applied lower amounts of insecticide and had lower Biocide Indices (per ha) than growers of non-Bt cotton, some of this advantage was due to a reduction in non-bollworm insecticide. Indeed, the Biocide Index for all farmers in the population actually increased with the introduction of Bt cotton. The results indicate the complexity of such studies on the socio-economic and environmental impacts of GM varieties in the developing world.

Reductions in insecticide use from adoption of Bt cotton in South Africa: impacts on economic performance and toxic load to the environment

The study reported presents the findings relating to commercial growing of genetically-modified Bt cotton in South Africa by a large sample of smallholder farmers over three seasons (1998/99, 1999/2000, 2000/01) following adoption. The analysis presents constructs and compares groupwise differences for key variables in Bt v. non-Bt technology and uses regressions to further analyse the production and profit impacts of Bt adoption. Analysis of the distribution of benefits between farmers due to the technology is also presented. In parallel with these socio-economic measures, the toxic loads being presented to the environment following the introduction of Bt cotton are monitored in terms of insecticide active ingredient (ai) and the Biocide Index. The latter adjusts ai to allow for differing persistence and toxicity of insecticides. Results show substantial and significant financial benefits to smallholder cotton growers of adopting Bt cotton over three seasons in terms of increased yields, lower insecticide spray costs and higher gross margins. This includes one particularly wet, poor growing season. In addition, those with the smaller holdings appeared to benefit proportionately more from the technology (in terms of higher gross margins) than those with larger holdings. Analysis using the Gini-coefficient suggests that the Bt technology has helped to reduce inequality amongst smallholder cotton growers in Makhathini compared to what may have been the position if they had grown conventional cotton. However, while Bt growers applied lower amounts of insecticide and had lower Biocide Indices (per ha) than growers of non-Bt cotton, some of this advantage was due to a reduction in non-bollworm insecticide. Indeed, the Biocide Index for all farmers in the population actually increased with the introduction of Bt cotton. The results indicate the complexity of such studies on the socio-economic and environmental impacts of GM varieties in the developing world.

The effects of the insecticide chlorpyrifos on spider and Collembola communities

The effects of chlorpyrifos on aquatic systems are well documented. However, the consequences of the pesticide on soil food webs are poorly understood. In this field study, we hypothesised that the addition of a soil insecticide to an area of upland grassland would impact spider and Collembola communities by decreasing numbers of spiders, consequently, causing an increase in detritivore numbers and diversity. Chlorpyrifos was added to plots on an upland grassland in a randomised block design. Populations of Collembola and spiders were sampled by means of pitfall traps (activity density) and identified to species. Twelve species of Collembola were identified from the insecticide-treated and control plots. Species diversity, richness and evenness were all reduced in the chlorpyrifos plots, although the total number of Collembola increased ten-fold despite the abundance of some spider species being reduced. The dominant collembolan in the insecticide-treated plots was Ceratophysella denticulata, accounting for over 95% of the population. Forty-three species of spider were identified. There were a reduced number of spiders in insecticide-treated plots due mainly to a lower number of the linyphiid, Tiso vagans. However, there was no significant difference in spider diversity between the control and insecticide treatments. We discuss possible explanations for the increase in abundance of one collembolan species in response to chlorpyrifos and the consequences of this. The study emphasises the importance of understanding the effects of soil management practices on soil biodiversity, which is under increasing pressure from land development and food production. It also highlights the need for identification of soil invertebrates to an 'appropriate' taxonomic level for biodiversity estimates. (C) 2007 Elsevier GrnbH. All rights reserved.

Interaction of pesticides with p-glycoprotein and other ABC proteins: A survey of the possible importance to insecticide, herbicide and fungicide resistance

P-glycoproteins (p-gps) are ubiquitous membrane proteins from the ABC (ATP-binding cassette) family. They have been found in many animals, bacteria, plants and fungi and are extremely important in regulating a wide range of xenobiotics including pesticides. P-gps have been linked to xenobiotic resistance, most famously in resistance to cancer drug treatments. Their wide substrate range has led to what is known as "multidrug resistance", where resistance developed to one type of xenobiotic gives resistance to a different classes of xenobiotic. P-gps are a major contributor to drug resistance in mammalian tumours and infections of protozoan parasites such as Plasmodium and Leishmania. There is a growing body of literature suggesting that p-gps, and other ABC proteins, are important in regulating pesticide toxicity and represent potential control failure through the development of pesticide resistance, in both agricultural and medical pests. At the same time, aspects of their biochemistry offer new hope in pest control, in particular in furthering our understanding of toxicity and offering insights into how we can improve control without recourse to new chemical discovery. (c) 2008 Elsevier Inc. All rights reserved.

Identification of mutations conferring insecticide-insensitive AChE in the cotton-melon aphid, Aphis gossypii Glover

We have identified two mutations in the ace1 gene of Aphis gossypii that are associated with insensitivity of acetylcholinesterase (AChE) to carbamate and organophosphate insecticides. The first of these, S431F (equivalent to F331 in Torpedo californica), is associated with insensitivity to the carbamate insecticide pirimicarb in a range of A. gossypii clones. The S431F mutation is also found in the peach-potato aphid, Myzus persicae (Sulzer), and a rapid RFLP diagnostic allows the identification of individuals of both aphid species with a resistant genotype. This diagnostic further revealed the presence of S431 in several other pirimicarb-susceptible aphid species. The serine at this position in the wild-type enzyme has only been reported for aphids and provides a molecular explanation of why pirimicarb has a specific aphicidal action. A less specific insensitivity to a wide range of carbamates and organophosphates is associated with a second mutation, A302S (A201 in T. californica).

Gene transcription in Daphnia magna: effects of acute exposure to a carbamate insecticide and an acetanilide herbicide.

Daphnia magna is a key invertebrate in the freshwater environment and is used widely as a model in ecotoxicological measurements and risk assessment. Understanding the genomic responses of D. magna to chemical challenges will be of value to regulatory authorities worldwide. Here we exposed D. magna to the insecticide methomyl and the herbicide propanil to compare phenotypic effects with changes in mRNA expression levels. Both pesticides are found in drainage ditches and surface water bodies standing adjacent to crops. Methomyl, a carbamate insecticide widely used in agriculture, inhibits acetylcholinesterase, a key enzyme in nerve transmission. Propanil, an acetanilide herbicide, is used to control grass and broad-leaf weeds. The phenotypic effects of single doses of each chemical were evaluated using a standard immobilisation assay. Immobilisation was linked to global mRNA expression levels using the previously estimated 48h-EC(1)s, followed by hybridization to a cDNA microarray with more than 13,000 redundant cDNA clones representing >5000 unique genes. Following exposure to methomyl and propanil, differential expression was found for 624 and 551 cDNAs, respectively (one-way ANOVA with Bonferroni correction, P

The impact of an insecticide on insect flower visitation and pollination in an agricultural landscape

1 Pesticides are considered a threat to pollinators but little is known about the potential impacts of their widespread use on pollinators. Less still is known about the impacts on pollination, comprising the ecosystem service that pollinators provide to wildflowers and crops. 2 The present study measured flower visitation and pollination in an agricultural landscape, by placing potted flowering plants (Petunia sp.) in vine fields sprayed with a highly toxic insecticide (fenitrothion). During two sampling rounds, insect visitors to the petunias were observed and measures of pollination were recorded by counting and weighing seeds. 3 In the earlier sampling round, a lower species richness of insect visitors was observed in fields that had received an early application of insecticide. No negative impacts were found from later applications. The results obtained suggest a greater potential harm to insect pollinators and flower visitation as a result of insecticide application early in the season. 4 No reduction in pollination was found in fields that received an early insecticide application. Pollination was greater with two insecticide applications between sampling rounds rather than one application. 5 In the present study system, insecticide application had a negative effect on pollinators but a possible positive effect on pollination services. In some cases, it may be that actions for conserving biodiversity will not benefit pollination services to all plants.

Legume type and temperature effects on the toxicity of insecticide to the genus Callosobruchus (Coleoptera: Bruchidae)

Three bruchid pest species, Callosobruchus maculatus, Callosobruchus chinensis and Callosobruchus rhodesianus, were studied for their response to insecticide toxicity taking into account the separate and interactive effects of temperature and pre-adult food. The food types used were cowpea (Vigna unguiculata) and mungbean (Vigna radiata). Callosobruchus maculatus was the most tolerant to malathion and the least affected by temperature change while C. rhodesianus was the least tolerant. Over a 4 C range (23, 25, 27 C), there was generally a significant impact of temperature on the tolerance of the three species to the insecticide. The food type on which the insects developed influenced considerably the degree of insecticide tolerance. Callosobruchus maculatus and C. chinensis populations reared onmungbean had higher tolerance to malathion than their counterparts reared on cowpea, but the opposite was observed in C. rhodesianus populations. The food influence in this study suggested an ancestral cause or fitness cost depending on the species. The interaction of food-by-temperature had no significant effect on malathion toxicity to this genus. Correlation analysis showed C. chinensis to be relatively less sensitive to insecticide concentration over the range studied compared with the other two species.

Synergistic effects of geographical strain, temperature and larval food on insecticide tolerance in Callosobruchus maculatus (F.)

This study investigated the multifactorial interaction of various environmental factors including 17 geographical strain (Brazil, Cameroon and Yemen strains), temperature, dose and larval food 18 (cowpea and mungbean) on the response of Callosobruchus maculatus adult to insecticide. All 19 the main factors, their two-way interactions and the four-way interaction had significant effects 20 on C. maculatus response to malathion (an organophosphate insecticide). However, the three-21 way interactions were not statistically significant (except strain x food x dose, P = 0.002). The 22 2 Brazil strain was the most responsive to temperature irrespective of the larval food type. The 23 impact of food type differs from one strain to the other, for instance, the food that imparts higher 24 tolerance in a strain might reduce the tolerance in another. Likewise, the hierarchy of tolerance 25 among the cowpea-reared strains (Brazil > Cameroon > Yemen) was totally different from the 26 mungbean-reared strains (Cameroon > Yemen > Brazil). The reasons for these differences were 27 discussed in the light of their impact on C. maculatus management. The management of both C. 28 maculatus and development of resistance could be complex, hence, the states of a variety of 29 environmental factors need to be considered. This is necessary in order to maximize management 30 success of this bruchid especially in tropical/subtropical developing countries.

Variation in the sensitivity of Callosobruchus (Coleoptera: Bruchidae) acetylcholinesterase to the organophosphate insecticide malaoxon: effect of species, geographical strain and food type

BACKGROUND: Bruchid beetles, Callosobruchus species, are serious pests of economically important grain legumes; their activity in stores is often controlled by use of synthetic insecticides. Esterases are known to be involved in insecticide resistance in insects. However, there is dearth of information on esterase activity in the genus Callosobruchus. In this study we investigated the effect of species, geographical strain and food type on the variation of acetylcholinesterase (AChE) activity and its inhibition by malaoxon (malathion metabolite) using an in vitro spectrophotometric method. RESULT: AChE activity varied significantly among species and strains and also among legume type used for rearing them. Generally irrespective of species, strain or food type, the higher the AChE activity of a population, the higher its inhibition by malaoxon. C. chinensis had the highest AChE activity of the species studied and in the presence of malaoxon it had the lowest remaining AChE activity, while C. rhodesianus retained the highest activity. CONCLUSION: A firsthand knowledge of AChE activity in regional Callosobruchus in line with the prevailing food types should be of utmost importance to grain legume breeders, researchers on plant materials for bruchid control and pesticide manufacturer/applicators for a robust integrated management of these bruchids.

Sublethal neonicotinoid insecticide exposure reduces solitary bee reproductive success

1. Pollinating insects provide crucial and economically important ecosystem services to crops and wild plants, but pollinators, particularly bees, are globally declining as a result of various driving factors, including the prevalent use of pesticides for crop protection. Sublethal pesticide exposure negatively impacts numerous pollinator lifehistory traits, but its influence on reproductive success remains largely unknown. Such information is pivotal, however, to our understanding of the long-term effects on population dynamics. 2 We investigated the influence of field-realistic trace residues of the routinely used neonicotinoid insecticides thiamethoxam and clothianidin in nectar substitutes on the entire life-time fitness performance of the red mason bee Osmia bicornis. 3 We show that chronic, dietary neonicotinoid exposure has severe detrimental effects on solitary bee reproductive output. Neonicotinoids did not affect adult bee mortality; however, monitoring of fully controlled experimental populations revealed that sublethal exposure resulted in almost 50% reduced total offspring production and a significantly male-biased offspring sex ratio. 4 Our data add to the accumulating evidence indicating that sublethal neonicotinoid effects on non-Apis pollinators are expressed most strongly in a rather complex, fitness-related context. Consequently, to fully mitigate long-term impacts on pollinator population dynamics, present pesticide risk assessments need to be expanded to include whole life-cycle fitness estimates, as demonstrated in the present study using O. bicornis as a model.

Poor survival on an artificial diet of two genotypes of the aphid Myzus persicae: a fitness cost of insecticide resistance?

A fully susceptible genotype (4106A) of Myzus persicae survived the longest on an artificial diet and, in several of the eight replicates, monitoring was terminated when the culture was still thriving. A genotype with elevated carboxylesterase FE4 at the R3 level (800F) had a mean survival of only 98.13 days, whereas 794J, which combines R3 E4 carboxylesterase with target-site resistance (knockdown resistance), survived for the even shorter mean time of 84.38 days. The poorer survival of the two genotypes with extremely elevated carboxylesterase-resistance was not the result of a reluctance to transfer to new diet at each diet change. Although available for only two replicates, a revertant clone of 794J (794Jrev), which has the same genotype as 794J but the amplified E4 genes are not expressed leading to a fully susceptible phenotype, did not appear to survive any better than this clone. This suggests that the poor survival on an artificial diet of the extreme-carboxylesterase genotypes is not the result of the cost of over-producing the enzyme. The frequency of insecticide-resistant genotypes is low in the population until insecticide is applied, indicating that they have reduced fitness, although this does not necessarily reflect a direct cost of expressing the resistance mechanism.

Bt cotton, pesticides, labour and health - A case study of smallholder farmers in the Makhathini Flats, Republic of South Africa

This paper describes some of the results of a detailed farm-level survey of 32 small-scale cotton farmers in the Makhathini Flats region of South Africa. The aim was to assess and measure some of the impacts (especially in terms of savings in pesticide and labour as well as benefits to human health) attributable to the use of insect-tolerant Bt cotton. The study reveals a direct cost benefit for Bt growers of SAR416 ($51) per hectare per season due to a reduction in the number of insecticide applications. Cost savings emerged in the form of lower requirements for pesticide, but also important were reduced requirements for water and labour. The reduction in the number of sprays was particularly beneficial to women who do some spraying and children who collect water and assist in spraying. The increasing adoption rate of Bt cotton appears to have a health benefit measured in terms of reported rates of accidental insecticide poisoning. These appear to be declining as the uptake of Bt cotton increases. However, the understanding of refugia and their management by local farmers are deficient and need improving. Finally, Bt cotton growers emerge as more resilient in absorbing price fluctuations.

Explaining contradictory evidence regarding impacts of genetically modified crops in developing countries. Varietal performance of transgenic cotton in India

A study of the commercial growing of different varieties of Bacillus thuringiensis (Bt) cotton compares the performance of growing official and unofficial hybrid varieties of Bt cotton and conventional (non-Bt) hybrids in Gujarat by 622 farmers. Results suggest that the official Bt varieties (MECH 12 and MECH 162) significantly outperform the unofficial varieties. However, unofficial, locally produced Bt hybrids can also perform significantly better than non-Bt hybrids, although second generation (F-2) Bt seed appears to have no yield advantage compared to non-Bt hybrids but can save on insecticide use. Although hybrid vigour is reduced, or even lost, with F-2 seed the Bt gene still confers some advantage. The F-2 seed is regarded as 'GM' by the farmers (and is sold as such), even though its yield performance is little better than the non-GM hybrids. The results help to explain why there is so much confusion arising from GM cotton release in India.

Perceptions of the impacts of genetically modified cotton varieties: a case study of the cotton industry in Gujarat, India

The paper reports the findings of a study designed to consider the impact of the adoption of Bt cotton on markets, businesses, and institutional arrangements in India. Given that evidence to date suggests that widespread adoption of Bt cotton by farmers is likely to increase production, this study aims to assess possible implications for markets (access to inputs, prices of inputs and outputs, etc.) and local industries and to identify potential winners and losers. The results suggest that there are impacts on the cotton industry following from the release of Bt hybrids, and so far the impacts are most noticeable "upstream" (i.e., the input suppliers), where companies are rapidly moving away from the sale of bollworm insecticide and attempting to sell Bt seeds. Seed companies are looking for partnerships with Monsanto, the owner of the Bt gene. One reason that companies are keen to move away from insecticide is so they can avoid the need for credit supply to their customers. Seed purchase is not normally through credit, whereas insecticide purchase is. Issues for companies "downstream" (gins, textile manufacturers) relate more to the better quality of Bt cotton and the need for adequate segregation of Bt and non-Bt cotton.