Richa Dubey, Alisha Shekh, Anusuiya Panda

Introduction
Climate change is an important determinant of abundance and distribution of species. It is concerned with everyone since it posess potential threat to environment, and agricultural productivity and production throughout the world. It has implications for livelihood and survival of human beings. According to Intergovernmental Panel on Climate Change (IPCC, 2001), it is defined as change in climate over time, either due to natural variability or as a result of human activity. The rise in global climate temperature is the result of the enhanced green house effect that is caused due to the increased levels of green house gasses (GHG) like Carbon-dioxide (CO2), Chlorofluorocarbon (CFC), Methane (CH4 ) and Nitrous oxide (N2O) in the atmosphere. For species to survive in the changing climates, they must either adapt in situ to new conditions or shift their distributions in pursuit of more favourable ones. Many insects have large population sizes and short generation times, and their phenology, fecundity, survival, selection and habitat use can respond rapidly to the climate change. These changes to insect life-history may in turn produce rapid changes in their abundance and distribution. Increased temperature will cause insect pests to be more abundant and almost all insects will be affected by changes in temperature.

The climatic change impacts on pests may include:
  • Changes in diversity and abundance of insect pests
  • Changes in geographical distribution of insect pests
  • Increased overwintering insects
  • Rapid population growth and no. of generations
  • Changes in synchrony between insect pests and their host crops
  • Introduction of alternative hosts plants
  • Changes in host plant resistance
  • Changes in insect biotypes
  • Changes in tritrophic interactions
  • Impact on extinction of species
  • Changes in activity and relative abundance of natural enemies
  • Increased risk of invasive pest species
  • Reduced efficacy of crop protection technologies

Impact of Climate Change and Insects-Pests
The increase in temperature associated with climatic change, would impact crop pest insect populations in several complex ways like, extension of geographical range, increased over-wintering, changes in population growth rate, increased number of generations, extension of development season, changes in crop pest synchrony, changes in interspecific interactions, increased risks of invasions by migrant pests and introduction of alternative hosts and over-wintering hosts.

a) Changes in insect- Pests diversity- The Western Ghats in India is the only habitat to many rare, endemic and exotic species of colourful butterflies in the world. In the present day scenario, many butterfly species are under a real threat due to depletion of the natural vegetation for various anthropogenic developmental activities.

b) Expansion of geographical ranges - Overwintering survival and timing of the commencement spring are important at higher latitudes, leading to population build-up of, for example, global warming results altitude wise range expansion and increased overwintering survival of corn earworms Heliothis zea (Boddie) and Helicoverpa armigera (Hubner) may cause heavy yield loss and put forth major challenge for pest management in maize, a staple food crop of USA.

c) Changes in Insect Phenology- Members of the order Lepidoptera are the best examples of such phenological changes. Changes in butterfly phenology have been reported in UK, where 26 of 35 species have advanced their first appearance. Early adult emergence and an early arrival of migratory species have also been reported for aphids in the UK.

d) Introduction of invasive alien species- Climate change can as well promote arrival and establishment of the exotic species. Risk of introduction invasive alien species, increase with global climate change.

e) Pest population dynamics and outbreaks- Changes in climatic variables have led to increased frequency and intensity of outbreaks of insect-pests. Outbreak of sugarcane woolly aphid Ceratovacuna lanigera Zehntner in sugarcane belt of Karnataka and Maharashtra states during 2002-03 resulted in 30% yield losses.

f) Crop-pest interactions- The capacity of an herbivore insect to complete its development depends on the adaptation to both, the environmental conditions and the host plant. This has been shown by gypsy moth attacking the Red maple (Acer rubrum L.) and Sugar maple (A. saccharum) which had reduced larval weight, increased feeding time and prolonged development. The large outbreaks observed in the expansion areas on the new hosts may be explained either by the high susceptibility of the hosts or by the inability of natural enemies to locate the moth larvae on an unusual hosts or environment.

g) Increased incidence of insect vectored plant diseases- Climate change may lead to more incidence of insect transmitted plant diseases through range expansion and rapid multiplication of insect vectors. Increased temperatures, particularly in early season, have been reported to increase the incidence of viral diseases in potato due to early colonization of virus bearing aphids, the major vectors for potato viruses in Northern Europe.

Impact of Climate Change on the Pest Management Strategies

a)Breakdown of host plant resistance- With global temperature rise and increased water stress, tropical countries like India may face the problem of severe yield loss in sorghum due to breakdown of resistance against midge Stenodiplosis sorghicola (Coq.) and spotted stem borer, Chilo partellus Swinhoe. There will be an increased impact on insect pests which benefit from reduced host defences as a result of the stress caused by the lack of adaptation to suboptimal climatic conditions.

b) Transgenic crops- In recent advancement of integrated pest management, insect resistant transgenics expressing the Bacillus thuringiensis (Berliner) (Bt) insecticidal protein (delta-endotoxin) were developed. However, these transgenic plants showed a reduction in the level of toxin protein during periods of high temperature, elevated CO2 levels, or drought, leading to decreased resistance to insect pests. Cotton bollworm, Heliothis virescens (F.), destroyed Bt cottons due to high temperatures in Texas, USA.

c) Natural enemies- The majority of insects are benign to agro-ecosystems, and there is considerable evidence to suggest that this is due to population control through interspecific interactions among insect pests and their natural enemies and pathogens, parasites, and predators. Oriental armyworm, M. separata populations increased during extended periods of drought (which is detrimental to the natural enemies), followed by heavy rainfall because of the adverse effects of drought on the activity and abundance of the natural enemies of this pest.

d) Bio-pesticides and Synthetic Insecticides- Natural plant products, entomo-pathogenic viruses, fungi, bacteria, nematodes, and synthetic pesticides are highly sensitive to the environment. Increased temperature will increase the activity of some of the insecticides. Diflubenzuron (an insect growth regulator (IGR)) caused rapid mortality at higher temperatures and was more efficient at 35°C. However, the biological activity of the entomopathogenic fungus, Beauveria bassiana (Balsamo), is reduced at temperatures >25°C.

e) Implications for Food Security- The greatest challenge in the coming century is to double the present levels of food production to meet the needs of ever increasing population by sustainable use of shrinking natural resource base. The climate change is likely to affect the extent of entomophilies pollination by disrupting the synchrony between plant-pollinator life cycles with an estimated risk of reduction in world food production by one third.

Adaptation of agriculture to changing pest scenario due to climate
No doubt, understanding and dealing with the problem of abiotic stresses and crop insect pest interactions under the influence of changing climate is difficult task. Some of the strategies that we would feel useful in tackling the issue are pointed out below.
  • Sensitization of Stakeholders about Climate Change and its Impacts.
  • Farmers Participatory Research for Enhancing Adaptive Capacity.
  • Promotion of Resource Conservation Technologies (RCTs).

Conclusion
Climate change now a day is globally acknowledged fact. It has serious impacts on diversity, distribution, incidence, reproduction, growth, development, voltisim and phenology of insect pests. Climate changes also affect the activity of plant defense and resistance, biopesticides, synthetic chemicals, invasive insect species, expression of Bt toxins in transgenic crops. Dealing with the climate change is really tedious task owing to its complexity, uncertainty, unpredictability and differential impacts over time and place. Understanding abiotic stress responses in crop plants, insect-pests and their natural enemies is an important and challenge ahead in agricultural research. Impacts of climate change on crop production mediated through changes in populations of serious insect-pests need to be given careful attention for planning and devising adaptation and mitigation strategies for future pest management programmes. Therefore, there is a need to have a concerted look at the likely effects of climate change on crop protection, and devise appropriate measures to mitigate the effects of climate change on food security.