Biodiversity in a Forest-Agriculture Mosaic—The Changing Face of West African Rainforests

The tropical forest zone in West Africa has experienced centuries of human modification, leading to a substantial decline in forest cover and loss of forest biodiversity. Norris et al. (2010) identify agricultural expansion as the main cause of forest loss and degradation. In addition, the study examines biodiversity of plants, invertebrates, and vertebrates, as a measure of mean species richness across primary forest, logged forest, secondary forest, fallow, tree plantation, perennial crop, annual crop, and clearcut regions. The data show that across all biodiversity groups, there is a significant overall loss of forest species as tree cover is reduced and vegetation structure simplified. Forests are also intrinsically linked to the livelihoods of locals by providing food, fuel, fiber, and a range of ecosystem services to over 200 million people. Therefore, Norris et al. argue for multi-functional conservation solutions, which attempt to recognize and value the wide range of services forests provide. Further studies of this region can provide insights for developing policies that avoid comparable levels of degradation in other African forest regions, which are still largely untouched. Anastasia Kostioukova
Norris, K., Asase, A., Collen, B., Gockowski, B., Mason, J., Phalan, B., Wade, A., 2010. Biodiversity in a forest-agriculture mosaic – The changing face of West African rainforests. Biological Conservation 143, 2341–2350.

Rapid population growth coupled with 4–5% per annum urbanization has turned West Africa’s lush tropical forest landscape into a forest-agriculture mosaic. From 1988 to 2007, agricultural expansion has been credited with an increase of 7.3 million ha in harvest area of commercial commodities and food staples, such as cassava (Manihot esculenta), plantain (Musa x paradisiacal), cocoyam (Colocasia spp.), oil palm (Elaeis guineensis), and cocoa (Theobroma cacao). In face of growing food demands, West Africa’s limited access to new technologies and poor investment in agricultural research has lead to yield stagnation. Subsequently, instead of increasing yields from existing agricultural practices, West Africans transformed forests into farms thereby increasing the overall amount of land under cultivation. As a result, numerous forest species became threatened with extinction.
Norris et al. aimed to estimate changes in biodiversity across forest and modified forests, using 25 plant, 44 invertebrate, and 18 vertebrate species for comparison. Although richness of endemic species tends to decline in modified habitats (i.e. logged and secondary forests), the data show that in some instances overall species richness increases. This can be explained by non-forest species and habitat generalists replacing many of the native forest species. For example, in cases of liberation thinning, which involve the cutting of lianas and climbers, and girdling of non-commercial trees, richness and diversity of non-native butterfly species increased. Considering that West Africa’s remaining dense forests are often fragmented, Norris et al. concluded that larger fragments held more species of trees, and also a higher proportion of rare species, than smaller fragments.
The authors suggest that further studies be conducted, since data collected in human-modified landscapes are patchy, and prone to a number of generic problems that affect biodiversity datasets. As a solution to forest degradation, Norris et al. encourage forest and agro-forestry systems to produce crops that store significant amounts of carbon, such as cocoa. These crops could be cultivated as carbon credit plants, and brought to either of the two carbon offset markets. In the larger, compliance market, companies, government, or other players buy such carbon credits to comply with caps on total amount of greenhouse gases they are allowed to emit. In the second, much smaller market, individuals, government, or companies voluntarily mitigate their own carbon dioxide emissions in an effort to be more sustainable. Participating in global carbon dioxide reduction markets provide West African farmers with financial incentives to protect local ecosystems by replanting and retaining tree cover.
Additional sources of West African land-use changes from forest to agriculture were attributed to logging, mining, and hydropower activities. These bring infrastructure (i.e. roads), which make the forest interior more accessible to farmers. West Africa’s severe forest degradation levels serve as potent reminder of what might happen to Central Africa’s undisturbed wild forest areas. Norris et al. suggest that studying West African forest loss would lead to smarter conservation efforts to combat environmental degradation foreshadowed in Central Africa’s future. 

Conservation Agriculture and Smallholder Farming in Africa— the Heretics’ View

Conservative agriculture (CA) is claimed to be a panacea to issues of poor agricultural productivity and soil degradation in Sub-Saharan Africa (SSA). CA methods are said to increase and stabilize yields and reduce labor requirements, while improving soil fertility and reducing erosion. However, CAs will only work when a number of agronomic management practices are applied simultaneously. Although showing great promise in controlled experimental conditions with added inputs such as fertilizers and herbicides, CAs gain little actual foothold on African farms. The constraints identified by Giller et al. (2009) include: a low degree of mechanization within the smallholder system; lack of appropriate soil fertility management options; problems of weed control under no-till systems; lack of credit; lack of market for grain legumes; lack of appropriate technical information; competition for crop residues in mixed crop–livestock systems; and limited availability of household labor. Giller et al. determine that each bio-physical and socio-economic environment determines the degree of CA success. The review concludes that under present circumstance CAs can offer substantial benefits to some farmers, but are inappropriate for most resource-constrained farmers in SSA. Anastasia Kostioukova
Giller, K., Witter, E., Corbeels, M., Tittonell, P., 2009. Conservation agriculture and smallholder farming in Africa: The heretics’ view. Field Crops Research 114, 23–34.

CA techniques are said to increase biological processes above and below ground leading to resource-efficient crop production. The three principles key to CAs are minimal or no mechanical soil disturbance, permanent organic soil cover, and diversified crop rotation. It is hard to assess CA practices, especially in demonstration programs, which include additional inputs such as fertilizers, herbicides, and improved seeds. Treating CA methods as indivisible concepts makes it difficult to discern the true source of crop growth stimulation, and evaluate benefits of each principle separately. Giller et al. determine that CA practices are most successful when configured to the environmental and social conditions of each growing region.
Important limitations exist under mixed African farming systems, which put constraints on adopting CAs. For example, in semi-arid areas where livestock are of great importance in income and risk management, crop residues are used as fodder instead of soil cover. Further, CAs can only gradually improve soil quality and crop yield. In the short-term, yield losses or no yield benefits are just as likely— a risk many resource constraint farmers are unwilling to take. Also in their initial years, CA systems have greater requirements for weed control. This creates demand in financial resources for herbicides or raising manual labor input for weeding. In addition, Giller et al. found that initial reduction in ploughing may cause mineral immobilization by affecting the rate of mineral absorption into soil. To offset yield reduction, farmers would need access to additional fertilizer until a new mineralization equilibrium is achieved. Adoptions of other CA principles, such as crop rotations are feasible only in regions where a ready cash market is available for famers to sell surpluses of grain legumes. In such cases, crops such as the groundnut (Arachis hypogaea) and cowpea (Vigna unguiculata) could improve soil fertility and be extremely beneficial for subsequent yields.
Switching from traditional farming methods to CA practices requires large amounts of initial input. Undertaking major transformation in crop and soil management proves overwhelming for most SSA smallholder farms. Additional burdens lie in remolding sensitive cultural rules and practices, such as traditional gender roles in agriculture. However, Giller et al. admit certain social benefits that may be bestowed upon farmers in light of the sheer complexity of CA systems compared to traditional practices. The authors offer evidence in support of positive social externalities associated with CA implementation, such as improvements in problem solving capacity as well as cooperation within SSA farming communities.

African Legumes—A Vital but Under-Utilized Resource

In recent years, African agriculture and forestry has become more reliant on non-native species. However, indigenous plants are arguably better suited for Africa’s environment. The ability to fix gaseous nitrogen makes nodulated legumes especially well-adapted to drought and low soil nutrients. Sprent et al. (2009) review selected case studies of native African legumes in an effort to analyze ways in which modern methods can improve plant productivity. In particular, the review focuses on cowpea (Vigna unguiculata), rooibos (Aspalathus linearis), and several honeybush (Cyclopia sp.), as well as, additive gum arabic (Acacia senegal). The range of products derived from these plants can be used to alleviate poverty in Africa through food and income generation. Anastasia Kostioukova
Sprent, J., Odee, D., Dakora, F., 2009. African legumes: a vital but under-utilized resource. Journal of Experimental Biology 61, 1257–1265.

Traditionally, cowpea (Vigna unguiculata) is used as a human food crop, and has uses in medicine and animal feed. On the African continent, there are many different lines of nodulating cowpeas along a wide-range of nitrogen fixation ability. Some types are more efficient than others, and therefore breeding programs should extract germplasm from the best performers. Cowpea is especially rich in iron, and can be used to alleviate malnutrition in Africa. The protein rich Bambara groundnut (Vigna subterranea), similar to the peanut, is a balanced source of food as well. Some legumes in this genus have other special qualities. Beach pea (Vigna marina) grows in saline coastal areas. Salinity is, like drought, an increasingly global problem. Germplasm resistant to salinity could provide salinity tolerance in same subgenus crops. Further, some species in Vigna have tubes facilitating storage of nutrients and water. These organs are a useful trait in an increasingly dry and infertile world. Africa has a vast array of indigenous legumes, ranging from large rainforest trees to small annual herbs. The authors suggest that further studies done on the plants in the Vigna genus will be beneficial for targeting issues of malnutrition and food insecurity.
Gum arabic (Acacia senegal) is important for a wide variety of uses in the food industry, as well as for medicine and paper production. The authors only considered the variety senegal in detail as it produces the bulk of current gum production. Traits of the plant such as gum quality and amount produced should be improved if Africa hopes to sustainably grow and export gum arabic however. Further, Sprent et al. suggest reducing dependence on nitrogen fertilizers by identifying species most efficient in nitrogen fixation. However, this will be a daunting task without technological advances. Besides gum for food additives, growers should focus on health beverages for export. Important for the South African economy are unfermented legume teas made of rooibos (Aspalathus linearis) and several honeybrush (Cyclopia) species. Legume teas are low in tannins, but high in anti-oxidants. Unlike fermented tea, unfermented tea retains most nutrients and satisfies the increasing global market demand for healthy products.

Legume teas, adapted to growing in unfavorable conditions, are also used for cosmetics and pharmacological products. Breeding programs should breed in accordance to best quality and quantity of tea produced. Only ‘red type’ rooibos is used for the commercial production of tea. While having nitrogen-fixating nodules, this species can also grow in extremely poor acid soils, and has cluster roots and mycorrhizas that help nutrient uptake. Further, wild honeybrush fixes up to 90% of own nitrogen, while commercial cultivators fix less. The authors suggest focusing on taking wild germplasm and transforming it into acceptable agronomic variety for export. Africa’s Cape Floristic Region (CFR) is a biodiversity hot spot, perfectly suited for recruitment of wild materials. Varying climate and geomorphology results in numerous small areas with unique combinations of character, such as soil pH and nutrient content. CFR has a high level of endemism, and has evolved families with genera and species found only in this region. Diversity of host legumes is accompanied with a diversity of nodulating bacteria found on the roots of such plants. These can be developed further by breeding programs into legumes adapted to drought, contributing both to future climate instability management and growing efficiency. 

The Response of African Land Surface Phenology to Large Scale Climate Oscillations

A study done by Brown et al. (2010) explores the relationship between large-scale climate oscillations and land surface phenology metrics to determine influence of climate variability on the growing season. Spatial models were used to examine the distribution and interaction of these effects as determined by Normalized Differential Vegetation Index (NDVI) data. Specifically, 26 years of recorded data from North Atlantic Oscillation (NAO), Indian Ocean Dipole (IOD), Pacific Decadal Oscillation (PDO), and the Multivariate El Nino Southern Oscillation (ENSO) Index (MEI) were used to identify the most significant positive and negative correlations for the four climate indices in Eastern, Western, and Southern Africa. In the regions examined, the study found that the start of season (SOS) and cumulative NDVI of the growing season (cumNDVI) were significantly affected by variations in climate oscillations. Anastasia Kostioukova
Brown, M., de Beurs, K., Vrieling, A., 2010. The response of African land surface phenology to large scale climate oscillations. Remote Sensing of Environment 114, 2286–2296.

Satellite remote sensing has become a primary input to monitor food production in Africa. To produce enough food to feed their families, hundreds of millions of Africans rely on sufficient rainfall and moderate temperatures. These variables are sensitive to climate change. Therefore, understanding which climate oscillations are most influential and affect variation in phenology metrics from one year to the next can improve seasonal analysis and agriculture planning across the continent. The objective is to provide evidence of whether climate variability captured in the four indices has had a significant impact on the vegetative productivity of Africa during the past quarter century. The use of satellite imagery provides a unique vantage point for observing seasonal dynamics of the landscape that have implications for global climate change issues.
Although five phenology metrics were calculated in the model, only SOS and NDVI were considered in the analysis. Further, African growing seasons do not consistently fall within one calendar year. Therefore, SOS and NDVI were determined by using two 1.5 year time periods— Cycle 1: October year 1– March year 3; and cycle 2: April year 2– October year 3. In order to reduce noise during correlation and increase the signal for each climate index, the study aggregated monthly climate indices into four seasons: December, January, February (DJF); March, April, May (MAM); June, July, August (JJA); and September, October, November (SON). Using spatial models, Brown et al. examined how many pixels behaved differently under a null hypothesis, with a significance of less than a 0.1 p-value. Rejection rates of the null hypothesis indicated links between climate oscillations and crop yields.
Brown et al.’s results were consistent with observed patterns of farming and climate variation. For example, results for cycle 2 capture the rainy seasons in which most Eastern African crops are grown. These are known as the Ethiopian ‘belg’ season, the Somalian ‘gu’ season, and Kenya’s ‘long rains’ season. Overall results show that East Africa’s SOS and cumNDVI are particularly sensitive to PDO variations in March–April–May. In Western Africa, the PDO during the September–November period dominates the correlation surface for cumNDVI. While the growing season in Southern African is sensitive to variations in the ENSO as well as NAO. The IOD was found to have a virtually no influence on phenology in all three regions. Brown et al. determined that further research on large-scale climate oscillation could provide forecast into future agricultural production in Africa.

Adapting to Climate Change—Agricultural System and Household Impacts in East Africa

A study done by Thornton et al. (2009) examined maize and bean crop yield response to future climate change in three distinct climates—temperate/tropical highland (MRT), humid-subhumid (MRH), and arid-semiarid (MRA). The authors focused on East African countries (i.e., Burundi, Kenya, Rwanda, Tanzania, and Uganda). The data show that in some areas of East Africa climate change will increase yield and have beneficial effects on household food security and income levels. This was primarily found in high altitude MRT areas where an increase in temperature will favor crop growth. In MRH systems, only moderate yield losses can be expected. Severe crop yield decreases are predicted for lower altitude MRA climates. These anticipated system-level shifts will take place in a context characterized by high population growth rate, and subsequent food stress. The authors suggest that adaptation to weather variation will be most successful when determined at the household and local community levels. Anastasia Kostioukova
Thornton, P., Jones, P., Alagarswamy, G., Andersen, J., Herrero, M., 2009. Adapting to climate change: Agricultural system and household impacts in East Africa. Agricultural Systems 103, 73–82.

East Africa is climatically and topographically variable. In order to determine the response of crop yields to rising global temperatures in MRT, MRH, and MRA, the authors allocated production spatially within each country. Livestock-based systems were used due to an unavailability of sub-national crop distribution data. Further, for predicting maize and bean yields in 2030 and 2050, Thornton et al. overlaid simulated crop yields on areas where suitability had been determined for maize and bean production. The suitability factors are proper length of growing period (LGP) and suitable soil. In addition, the study incorporated four combinations of two rainfall and two greenhouse-gas emission scenarios. Since maize and beans are traditionally rainfed crops in East Africa, one drier model (HadCM3) and one wetter model (ECHam4) were used. Further, high-emission (A1FI) scenario and low-emission (B1) scenarios were used to predict future crop growth.
The study found that countries with more MRT areas are better suited for future climate change. The crops grown in these temperate, cooler climates will benefit from an increase in temperature. For example, Burundi in 2050 is predicted to have an overall crop yield increase of 9%. This is because a 9% decrease of crop yields in MRH systems will be offset by a larger 18% increase in MRT crop yield areas. Further, the authors determine that crop yield production may differ between 2030 and 2050. For example, bean production is predicted to increase in Tanzania 4% in 2030, but decrease 5% by 2050, presumably because of a temperature increase beyond maize and bean heat tolerance threshold of 20–22°C. Overall by 2050, bean and maize yields are projected to increase in Burundi, Kenya, and Rwanda, but decline in Tanzania and Uganda.
Shifting areas of farming from MRH and MRA areas to MRT systems could offset losses and be an effective response to novel temperatures in East Africa. The authors cite Kenya as an example in which crop production can increase 17% accompanying a shift from MRH to MRT farming. However, in areas with few MRT regions such as Tanzania and Uganda, shifting production may not be an option. In this case, breeding programs focused on heat-drought tolerant maize and bean varieties are a better option. Since by 2050, East Africa’s total crop yield will have a larger increase than anywhere else in Africa, a rise in regional trade could be a solution to offset yield losses and food insecurities in neighboring countries. In MRA systems, households switching to crop types such as sorghum and millet would be a good strategy to combat severe crop yield decreases by 2050. Adoption of livestock-orientated production may be another option. In addition, these anticipated system-level shifts will take place in a context characterized by a high population growth rate. Given variability in yield response and in households’ ability to adapt, investment in agricultural development will be crucial if demands are to be met in poverty alleviation and food security. 

Shifts in African crop climates by 2050, and the implications for crop improvement and genetic resources conservation

Climate is a major agricultural constraint in much of Sub-Saharan Africa. Expected global warming trends pose a substantial threat as temperatures begin to move outside historical experience. Burke et al. (2009) characterized climates under which Africa’s cereals need to be grown in the coming decades. The study identified Sudan, Nigeria, Cameroon, and Mozambique, as the set of countries whose current growing season temperatures are analogous to many future novel climates. These areas have crop varieties less sensitive to heat. In protection and conservation efforts, selected regions should be the focus of genetic resource extraction by international genebanks.—Ana Kostioukova
Burke, M., Lobell, D., Guarino L., 2009. Shifts in African crop climates by 2050, and the implications for crop improvement and genetic resources conservation. Global Environmental Change 19, 317–325.

Of all African poor, 70% are life-dependent on farming.  Given African farmers adaptability to past climate variability, it is likely that they will continue adopting new crop varieties and alter timing of planting, among other agronomic practices. However, due to the speed of future climate change, Burke et al. predict that rural farmers will be unable to adapt rapidly enough without outside help. Data show that nearly all crop regions move rapidly outside previous temperature ranges. For maize, growing season average temperatures will overlap only 58% of historical observations by 2025, 14% by 2050, and 3% by 2075. Millet temperatures will overlap by 54%, 12%, and 2% in 2025, 2050, and 2075, and sorghum temperatures will overlap by 57%, 15% and 3%.
Traditional breeding methods have had a long history of success in Africa. Domesticated crop varieties called landraces, are typically improved by farmer selection for favorable traits such as resistance to drought, heat, pests, and disease. Currently, African landraces are underrepresented in international genebanks. Most seeds in conservation are adapted to cooler climates, therefore, irrelevant for Africa’s future growing season temperatures.
Using Africa’s primary cereal crops—maize, millet, and sorghum—the study measures self-overlap margins of past and future growing season temperatures by country. Second, it evaluates the extent and location of places the current climates of which serve as analogs for the future climates of other countries. Burke et al. determined that climate analogs represent regions of crop genetic diversity highly relevant to future growing conditions on the continent, and thus a promising source of germplasm on which needed breeding efforts could be based. Fourteen countries have less than 50% overlap with their future temperatures, but have five or more countries as analogs that overlap at least 75% with their novel climates. The study also found that for maize, five countries have less than 50% self-overlap, and fewer than five analog countries. These nations are typically Sahelian countries, and are the hottest and driest of the cereal growing countries currently. The authors suggest switching to more heat resistant crops, such as sorghum and millet.
Burke et al. also measured self-overlap, and analogous overlap, of historical and predicted rainfalls. The data show that in 85% of countries rainfall self-overlaps. Therefore, climate change will have less of an affect on precipitation rate changes in Africa. Further, it was determined that good temperature analogs tend to be good precipitation analogs with some outliers. Sudan and Eritrea are good analogs to many other countries’ future temperatures. However, these countries are much drier than the median African crop climate. Therefore, are less appealing as sources for maize, sorghum, and millet genetic resource conservation.

Multi-Scale and multi-sites analyses of the role of rainfall in cotton yields in West Africa

In West and Central Africa cotton is irrigated by rainfall. Therefore, cotton yield relies on climate. The study done by Sultan et al. (2010) links climatology and agriculture, in an effort for weather forecast systems to anticipate year-to-year cotton yield variability through rainfall parameters. The study used data from one long-term time series, 1965–1990, in a single plot in Mali, and a second short-term time series, 1993–2003, in 28 Cameroon locations. Both locations provided data identifying length of rain season as the most salient rainfall parameter to affect crop yield. —Ana Kostioukova
Sultan, B., Bella-Medjo, M., Berg, A., Quirion, P., Janicot, S., 2010. Multi-Scale and Multi-sites Analyses of the Role of Rainfall in Cotton Yields in West Africa. International Journal of Climatology 30, 58–71.

Identifying the beginning of the rainy season would maximize cotton yield. Farmers could start sowing immediately, thus providing favorable conditions for cotton’s 20 mm of rainfall. Followed by, a period of 30 days in which no dry spell exceeds 7 days. Dry spells shortly after planting are disastrous for the crop. Therefore, incorrectly identifying the onset of rain season could lead to crop failure. The study also identified two critical periods, in early and in late cotton season, in which cotton is especially sensitive to water stress. These times are during sowing and cotton blooming, 60 to 90 days after sowing. There is no indication that dry spells during other periods of the rain season negatively affect cotton yield.
Exposing cotton to sufficient levels of water for the total growth cycle would hedge against crop failure. Additional data were found by Sultan et al. in support of rain season length and onset dates being the best indicators of high cotton yield when calculating cotton’s water requirement satisfaction index (CWRSI). This number is based on the relationship between water supply and demand cotton experienced during a given growing season. It is calculated as the ratio of seasonal actual evapotranspiration (AET) — the trade-off between evaporation and transpiration of a plant, to the seasonal crop water requirement (WR). Using CWRSI, the study could hypothetically shift the actual sowing date to before the onset of rain season.  The data show that yield tends to increase while sowing before onset date. Correctly identifying rainy season onset would be especially beneficial in the driest locations, which the authors found to be more sensitive to climate fluctuations, therefore, more vulnerable to crop failure.
Cotton is the main tradable crop of West and Central Africa. It is an important source of income for farmers, because it finances fertilizers, materials and animals needed for production of food. Current West African climate forecast parameters focus on total rainfall amount during rainy season. Therefore, offer no insight into length or onset of rain season. In order to correctly gauge yearly cotton yield fluctuations, Sultan et al. suggest focusing forecast studies on onset date and length of rainy season in West Africa. 

Mirid Bug outbreaks in multiple crops correlated with wide-scale adoption of Bt Cotton in China

A study by Lu et al. (2010) in Northern China’s six major cotton-growing provinces (i.e., Shanxi, Henan, Hebei, Shandong, Anhui, and Jiangsu), links planting transgenic Bt (Bacillus thuringiensis) cotton with an increase in mirid bugs (Heteroptera miridae). Before the adoption of Bt cotton in 1997, mirid bugs were considered low risk, low population density pests. However, since the adoption of the genetically engineered crop, mirid bug populations have dramatically increased. Before Bt cotton insecticide spray directed against the cotton bollworm (Helicoverpa armigera) was commonly used. It killed mirid bugs as well. The addition of Bt cotton proved highly effective against H. armigera and led to a discontinuation of insecticide spraying. However, mirid bugs are not susceptible to Bt toxin. With the reduction of insecticide sprays, Bt cotton became a breeding ground for these once harmless pests, so spraying had to be reinstalled.
Lu,Y.,Wu,K.,Jiang, Y., Xia, B. Li, P., Feng, H., Wyckhuys, K.,Guo, Y. 2010. Mirid Bug Outbreaks in Multiple Crops Correlated with Wide-Scale Adoption of Bt Cotton in China. Science 328, 1151–1154.

Lu et al. monitored 38 locations for mirid bug abundance and insecticide use throughout the study region during 1997–2008 and 1992–2008 respectively. Mirid bug populations gradually increased, showing a positive linear relationship to amounts of Bt cotton planted. While incidents of cultivators using mirid bug specific spray increased exponentially, with amount of Bt cotton planted. Bt cotton is genetically engineered to express δ-endotoxins (cry proteins). These toxins kill a large percentage of cotton bollworms, which lay eggs in cotton, before adulthood. However, cry proteins are harmless to mirid bugs.
Mirid bugs are attracted to flowering plants. The early flowering cotton plant plays host to mirid bugs in mid to late June. Before adoption of Bt cotton, the crop was sprayed with broad-spectrum H. armigera spray. This reduced the mirid bug population in the early summer. However, with the Bt cotton built-in target pest control, mirid bugs are allowed to breed unhindered, with large populations spilling over to later flowering plants (i.e., Chinese date, grapes, apples, peach, and pear).  The highly adaptable pests can easily attained outbreak densities, switch host crops and spread geographically.
Although Bt cotton was supposed to reduce the amount of insecticide needed, the study found that cotton needed to be sprayed anyway. Lu et al. concluded that transgenic crops might bring various direct and indirect effects on the ecology by influencing nontarget factors. A more-comprehensive risk management system may be key to creating an integrated pest management system, and ensuring the sustainability of transgenic technologies.