Insects feel the heat: Pest management expertise contributes to research on global climate change Findings from Peru suggest that global warming is already affecting the distribution of crop insect pests. CIP and its partners are analyzing the implications

The heat is on Global warming is with us, say scientists. Records show that average temperatures worldwide rose by 0.6ºC between 1900 and 1990. The latest models predict a further rise of between 1.4 and 5.8ºC by the year 2100. Along with hotter climates, we will have to contend with rising sea levels and more extreme weather events. These trends have momentous implications for agriculture. There will be a dual shift in crop and livestock production: away from the equator to more temperate latitudes; and into the hills to escape heat or floods. Farmers will face new threats to their livelihoods and, as always when disasters strike, the poor will be hardest hit. The international community is just beginning to come to grips with the challenges posed by global warming. The CGIAR system's first response was to form the Intercenter Working Group on Climate Change to coordinate activities and identify priority areas for future research. Recently the group proposed the theme "Beating the Heat: Climate Change and Rural Prosperity" as one of the system's new Challenge Programs. This proposal is being considered for implementation because of its high priority on the international research agenda. CIP is contributing with its expertise in integrated pest management (IPM). Predictions in this field, as in all others affected by global warming, are fraught with uncertainty, but scientists agree that the current balance of insect populations is almost certain to be upset. For instance, some insects react strongly to relatively small changes in temperature and rainfall. Their altered distribution could be one of the first indicators that global warming is taking hold. "Expect the unexpected," says CIP entomologist Aziz Lagnaoui. "Climate change will favor invaders over native species. Some insect pests will become more important while others will decline, but the net effect will be to increase the pressure of pests on crop yields and therefore on farmers' incomes." Lagnaoui's ideas may have seemed mere speculation until dramatic evidence emerged from a valley in southern Peru.

The Cañete Valley laboratory

Around 150 kilometers south of Lima, Cañete Valley is one of the powerhouses of Peruvian agriculture. For two-thirds of its length, the river that gives its name to the valley tumbles through steep gorges, carving its way through the western flanks of the Andes. But as it approaches the Pacific Ocean the current slows and deepens, entering a broader plain. Here, on the flat valley floor, farmers grow cotton, potato, sweetpotato and other crops in an intensive production system. Much of the harvest is destined for urban markets, especially Lima, or for export.

Cañete farmers face the usual array of insect pests that typically plague such systems, including the ubiquitous whitefly (Bemisia tabaci and related species). When whiteflies are few in number, their feeding on crops does little damage. But if sprayed, they soon develop resistance and multiply, especially in systems where cropping is year-round. At high population densities, whiteflies can devastate whole crop stands, giving them a characteristic "silver-leaf" or burned appearance. Whiteflies are also vectors of some serious viral diseases, particularly mosaic and mottle viruses.

The Bemisia genus is highly diverse, with many different biotypes and species occurring around the world. Until recently, only biotype A of B. tabaci - which is common throughout the tropics and usually causes only moderate yield loss - was found in Cañete Valley. In 2001, however, a more aggressive whitefly, biotype B, was identified. According to farmers, it arrived during an El Niño year when the climate in this part of Peru was hotter and drier than usual. But instead of disappearing when the weather reverted to normal, the pest apparently adapted to its new environment, where it is now inflicting severe damage on yields and farmers' incomes.

Biotype B was detected during routine surveys by Peru's national entomology service, whose scientists alerted Lagnaoui and his colleagues at CIP. The two institutions decided to make the valley the subject of a more detailed study, which would form part of the Whitefly IPM Project of the CGIAR Systemwide Program on Integrated Pest Management. Working with Pamela Anderson, an entomologist based at the Centro Internacional de Agricultura Tropical (CIAT) in Cali, Colombia, Lagnaoui and Peruvian colleagues carried out extensive fieldwork in Cañete Valley.

What they found was cause for serious concern. The presence of B. tabaci biotype B was bad enough, but it was not wholly unexpected because this insect has been found elsewhere in Latin America. Research revealed, however, that another whitefly, B. afer, had also arrived. This species, which is even more aggressive than biotype B of B. tabaci, is normally restricted to the hotter, drier climates of Africa and had never been reported before in the Americas.

Electrophoretic patterns in whitefly samples from Cañete Valley New biotechnology tools, such as RAPDS (randomly amplified polymorphic DNA), help to evidence differences between biotypes of the B. tabaci species

"B. afer is now widespread in the valley and is causing serious damage to crops there," says Lagnaoui. "On sweetpotato it is even out-competing biotype B of B. tabaci." Particularly worrying is the fact that farmers are increasing their pesticide applications to control the newcomers. The result could be rising levels of resistance, eventually leading to crashes in yields and incomes, as has been the case elsewhere in the developing world.

While Lagnaoui and his colleagues collect data on pest distributions, other CIP scientists are analyzing climate data for the valley to find out how its weather has changed over the past 50 years. The aim is to match the data on pest populations with information on changes in temperature and rainfall. If patterns are detected, the analysis will be broadened to cover other valleys on the Pacific Seaboard, with a view to obtaining a more comprehensive picture.

"At the moment, we are caught in the typical predicament of scientists who make discoveries of this kind," notes Lagnaoui. "Report too early, and you court accusations of inadequate science coupled with sensationalism in order to attract funding; report too late, and farmers, politicians and the public ask, why didn't you warn us?" Early confirmation of similar findings in other locations will ease that dilemma.

Tracking pest movements

There is good reason to suspect that the new pests have spread beyond Cañete Valley. An insect similar to the whitefly, the leafminer (Liriomyza huidobrensis), has, in less than ten years, risen from comparative insignificance as a minor pest on a few vegetables to the status of a serious international problem. Population explosions have been reported globally, with the most serious outbreaks occurring in the intensive production systems of Asia and Latin America. In Cañete Valley, the pest has long been reported on peas and beans but has recently begun to feed on other crops as well. More polyphagus tastes on the part of a pest are commonly the prelude to a steep rise in its numbers.

In these cases of rising population levels, it is difficult to single out the causes. Climate is one of a complex set of inter-related factors that could be causing the changes. Other are associated, for instance, with intensification of production. In leafminers as in whiteflies, pesticides seem to have been a large part of the problem, fostering resistant strains and killing off the pests' natural enemies. In Cañete Valley, resistance appears to have developed in leafminers when the pest was restricted to peas and beans. The spread to other crops probably has occurred since the most recent El Niño event raised temperatures in the valley.

Modern science is contributing to the analysis by providing tools that can help us to understand just how pests spread. At the request of Lagnaoui and his colleagues, for instance, a scientist in the USA is conducting detailed DNA analysis of different biotypes of leafminer, with a view to tracking their movements worldwide over the past decade. The tools of molecular biology will provide a clearer answer than human eyes can, because the different species of leafminer, like those of whitefly, are difficult to distinguish by appearance alone. "So far, the analysis suggests that the most widespread biotypes are Latin American in origin," says Lagnaoui.

Managing change

In the face of global climate change, IPM strategies and technologies may need a radical overhaul.

Increasingly, plant breeders will need to combine pest resistance with tolerance to factors such as heat and drought when they develop new varieties. The search for such tolerance has made good progress in a few dryland cereals, such as pearl millet, sorghum and durum wheat, but has been less successful - or hardly attempted at all - in most other crops. Flexible global arrangements will be needed to facilitate the speedy exchange of germplasm with the necessary resistance characteristics.

The shift away from chemical pesticides towards bio-insecticides will doubtless continue as an IPM strategy. Some bio-insecticides, however, are highly susceptible to rises in temperature and ultra-violet radiation. For example, the half-life of commercial preparations based on the granulosis virus - widely applied as a dust to stored potatoes to destroy the potato tuber moth and other pests - falls by 60 percent when temperatures rise from 25oC to 30oC. Storage temperatures in North Africa frequently reach 31oC and stand to go higher as global warming takes hold. Already, these preparations can rarely be applied in the field under tropical conditions, because - unless they are mixed with a UV-protectant - they become ineffective within a few hours.

"We must be alert and ready to respond quickly to changing conditions," says Lagnaoui. That implies a need to improve capabilities for detection of early signs of changes in pest pressure, strengthen links between all relevant partners and increase investment in farmer field schools and other participatory approaches that can help educate farmers to keep a close watch on their crops and deal effectively with problems as they arise. And these farm-level approaches will need to be linked to stronger public-sector advisory services at regional and national levels.

In short, the international community has its work cut out if it is to meet the challenges of global warming. CIP's IPM experts are poised and ready to help.

Climate change and insects: Some key questions The complex interactions between global climate change and crop insect pests raise some major questions: How will changes in temperature and rainfall affect pest populations and distributions? Pests vulnerable to high temperatures may decline in numbers or move to higher latitudes or altitudes. There could be population explosions in species that respond to higher rainfall or drought by increasing their feeding and/or breeding behavior. New biotypes and species could evolve. How will the increased atmospheric carbon associated with global warming affect plants and insects? It could stimulate plant growth, increasing the amount of feed available, although this effect may be offset by drought stress. More carbon could reduce the nutritive value of plants, causing some insect species to decline but others to multiply as they step up their feeding behavior. How will relationships between insect pests and their natural enemies change? Some natural control mechanisms could "decouple" as the populations of pests and predators react differently to changes in rainfall and temperature. How will crop resistance or tolerance to insects be affected? Some cultivars could prove more vulnerable to pests as a result of stress caused by higher temperatures or other climate changes. How will changes in the pressures from insect pests interact with those from diseases and weeds? The host plants available to insect pests could vary if warming favors some weeds over others. Changes in the populations of insect vectors of plant viral diseases may alter disease incidence. Climate could also induce changes in the incidence of fungal diseases.