Dr. G. V. Ramanjaneyulu, and Dr. T. A. V. S. Raghunath
Insect populations like all animal populations are governed by their innate capacity to increase as influenced by various abiotic and biotic factors. The changes caused by the natural evolutionary forces are accelerated with the human interventions. After the changes like depletion of natural resources, environmental pollution, extinction of certain species of plants and animals, the Climate Change particularly caused by inadvertent anthropogenic disturbances has become more evident. Projected carbon dioxide levels in the twenty first century are two to four times higher than the pre industrial era. Global climate change resulting in changes in temperature rise and precipitation patterns, could accentuate the vulnerability of agriculture. IPCC (International Panel on Climate Change) predicted that global mean temperature would rise between 0.9 to 3.50 C by the year 2100 (IPCC, 2001). Global warming may increase average water vapour and evaporation, increase in precipitation in high-altitude regions, significantly alter the Monsoon pattern resulting in long dry spells and heavy downpours and change in storm patterns which could influence the global movement of pests, especially pathogens.
In agricultural ecosystems, soil, plant and animal interactions are rarely persistent enough, in time and space, to provide the ecological stability but result in dynamic equilibrium. Pest shifts are observed with changes in the ecological balance. The natural balance between beneficial and harmful insects changes with the cropping patterns, pest management practices and variability in environment. Weather and Climate have an impact on the pest population. ‘Weather’ is short term variation of the atmosphere at a given time with respect to temperature, pressure, wind moisture, cloudiness and precipitation. ‘Climate’ is usually defined as the statistical collective of the weather of a specified area during a specific interval of time or as the prevailing or average weather conditions of an area over a long period. Climate change leads to shifts in the pest incidence, migration and viability thresholds. Today, farming and farmers lives are already effected by the pests and pest management practices they adopt. Hence, understanding the intricacies of climate change on pest management in agriculture is crucial.
Weather has both direct and indirect effects on the insect populations. The direct effects of weather on behavior and physiology are well documented. Reproductive biology of an insect may be affected both positively and negatively which ultimately affect its populations. Climate change would shift pest populations as it would shift important determinants of pest incidence, namely temperature, precipitation distribution, and wind pattern.
Temperature: All life survives with a certain narrow range of temperature. Deviations from this in optimum range on either side is tolerated to some extent, depending on the physiological adaptations of the concerned species or populations. Temperatures above or below these limits can prove lethal. Exposure to lethal high or low temperatures may result in instant killing or failure to grow and reproduce normally. Harmful effects of exposure to sub-lethal temperatures may be manifested at later critical stage like moulting or pupation. rise in temperature might also have a negative effect on delicate natural enemies such as hymenopteran parasitoides and small predators. This may effect natural enemy-pest relationship. For e.g. Brown Plant Hopper is 17 times more tolerant to 400 C than its predator Cyrtorrhynus lividipennis but wolf spider Paradosa pseudoannulata is tolerant to 40 0 C.
Moisture: Most terrestrial insects live in an environment, which is dry. The only source of water for insects is the water obtained with food material from their host plants. These insects have, therefore developed a variety of mechanisms to conserve water. In spite these mechanism, exceptionally dry air may prove lethal to most insects. Likewise, excessive moisture may also adversely affect many insects by encouraging disease outbreaks, affecting normal development and by lowering their capacity to withstand lower temperatures. The reproductive capacity of the insects is also affected by moisture but there are great differences in the capacity of different insects to tolerate conditions ranging from extreme dryness to near saturated environments. For example, incidence of Rice Hispa in Telangana region has increased in the last two years due to prevailing dry situations.
There is a shift observed from the leaf/fruit eating caterpillars to sucking pests in the recent years. While monoculture of crops/varieties and chemical pest management practices understood to have resulted resulted in such pest shifts, climate change also have also contributed for such shift. For example in cotton there is a shift towards sucking pests (mealy bugs, jassids) particularly after the introduction of Bt cotton. Similarly, Aphid incidence in Groundnut, Thrips and yellow mites in chillies are observed. Most of the sucking pests are also vectors of viral diseases. With increasing incidence of sucking pests viral diseases are also increasing e.g., Budnecrosis in Groundnut, Tobacco Streak Virus incidence in Cotton, and similar viral problems in most of the fruit crops, vegetables.
Other impacts of Climate change on pest incidence
a. Increases in UV-B radiation is likely due to depletion of ozone layer resulting in increased production of plant metabolites that might change the host-pathogen relationships and the status of the individual pest.
b. Under changed climatic condition, cropping pattern and intensity may be changed and to cope up the situation new varieties, or new methods of pest control or new chemicals to kill a pest may be released which might have either positive or negative impact on pests.
Ecological Pest management
Pest is not a problem but a symptom. Disturbance in the ecological balance among different components of crop ecosystem (biotic and abiotic) makes certain insects reach pest status. These problems of increasing pest incidences and pest shifts can be tackled only with better environmental friendly pest management practices. Ecological approaches to pest management should be based on knowledge and skill based practices to prevent insects from reaching damaging stages and damaging proportions by making best use of local resources, natural processes and community action’.
- Understanding crop ecosystem and suitably modifying by adopting suitable cropping systems and crop production practices. The type of pests and their behavior differs with crop ecosystem. Similarly the natural enemies’ composition also varies with the cropping systems.
- Understanding insect biology and behavior and adopting suitable preventive measures to reduce the pest numbers.
- Building Farmers knowledge and skills in making best use of local resources and natural processes and community action. Natural ecological balance which ensures that pests do not reach a critical number in the field that endangers the yield. Nature can restore such a balance if it is not meddled with too much.
In Andhra Pradesh such initiative implemented through Federations of Women Self Groups across the state in 18 districts in more than 3000 villages covering more than 14 lakh acres in 2008-09 in the name of ‘Non Pesticidal Management’ has shown that such eco-approaches can bring in both ecological and economic benefits to the farmers. This program started in 2004-05 with technical support from Centre for Sustainable Agriculture and financial and administrative support from Society for Elimination of Rural Poverty (SERP). The farmers in the villages are grouped into Field Schools and trained by the local civil society organisations. The regular and incidental technical support is institutionalized and community managed. The learning from this program are now considered by the ‘National Mission on Sustainable Agriculture’ as part of National Action Plan on Climate Change to be implemented across the country during the 11th five year plan.
 The aurthors can be contacted at Centre for Sustainable Agriculture, 12-13-445, Street no-1, Tarnaka, Secunderabad-500 017 email@example.com, http://www.csa-india.org