**4. Impact of climate change on insects, plants and their interactions**

Climate change has significant consequences in every field of agriculture. Climatic changes like temperature, precipitation, humidity and other meteorological components influence the relationship between insect pests and plants. Climate change has enhanced the pest population and their damage potential by increasing the distribution, improving survival rates and developing the adaptability of insect pests. The change in population, mobility, and insect pest behaviour is caused by increasing temperatures, changed precipitation patterns and disrupted gaseous composition of the atmosphere etc. A number of variables that decide how much plants can grow are influenced by climate change. At the same time, incidence of higher temperatures, decline in the supply of water and changes in soil conditions would actually make it harder for plants to flourish. The relationships between plants and insects are altered by increased CO2 and temperature, with important consequences for food security. Via warming acceleration of plant phenology creates mismatches between plants and insect pollinators. Likewise, changing the development rate of plant in relation to the development of insect can intensify/mitigate the effects of herbivore.

#### **4.1 Impact of climate change on insect pests**

The insect pests are seriously affected by overall rise in global average temperatures, weather pattern changes and severe climatic events. With these seasonal and long term changes the population dynamics of many insect pests would be influenced. Different climate patterns primarily affect insect ecosystems and their survival strategies. Significant climate change drivers like higher temperatures

and CO2 levels and lower soil humidity, have an effect on the nature of population of insect pests and results in subsequent crop losses. Abiotic parameters impose direct effects on the rate of distribution and abundance of insect pest populations by adjusting their growth, survival, reproductivity, dispersal and number of generations per season. Because of the rapid climate change, insect pests are developing increased overwintering stages and number of generations with rapid population growth. Temperature is said to cause direct effects among the abiotic factors. For example, increasing temperatures, from 1.5 to 2.5°C, will surely increase the winter survival and prolong the range of pink bollworm, *Pectinophora gossypiella* [40]. During extended periods of drought, followed by heavy rainfall oriental armyworm, *Mythimna separata*, the populations raises due to the undesirable effects of drought on the activity and abundance of natural enemies of this insect pest [41].

### **4.2 Impact of climate change on beneficial insects**

Climate change impacts the insect pest's natural enemies in a wide variety of ways. Plants grown under higher temperatures and CO2 and lower precipitation provides various nutritional opportunities for different insect pests, eventually affecting the fitness of insect pest- feeding predators and parasitoids [42]. Despite of a wide variety of host and parasitoid species, variability in precipitation is the key cause for differences in caterpillar parasitism. Parasitism of mealy bug is reduced under conditions of water stress combined with dry conditions in cassava, *Manihot esculenta* [43]. In relation to herbivore hosts and their movement, natural enemies locate their hosts based on their tolerance to environmental extremes. Predatory bugs, *Oechalia schellenbergii* were found to be more effective in destroying the cotton bollworm larvae when pea plants are cultivated at high CO2 levels [44]. Similarly, in feeding upon the aphid, *Aphis gossypii*, the coccinellid predator, *Leis axyridis*, was found to be more successful at higher CO2 levels [45].

In hot summers rather than in moderate summers, ladybird beetles (*Coccinella septempunctata*) reduce aphid populations (*Sitobion avenae*) more effectively [46]. Rise in temperature affects the production and release of volatile compounds and extra floral nectar by plants. These secretions help the insects to avoid the attack from natural enemies. Natural enemies need to undergo climate change for breeding purposes, after overcoming temperature extremes; they need to find hosts efficiently through a broad spectrum of temperature and humidity environments. *Trichogramma carverae*, the egg parasitoid fails to recognise hosts at temperature above 35°C [47] and reduces fertility at 30°C [48]. Some parasitoids evolve earlier than hosts in rapid response to temperature and often engage in the extinction of the parasitoid population in absence of the hosts. At elevated temperatures, the rate of insect parasitism will be reduced as host species emerge and move through the susceptible stages quickly before the appearance of parasitoids. Mild winters in temperate regions enhance the survival of parasitoids. Ex: Aphid parasitoids from cereal crops become active during winter and reduce spring aphid populations [49]. The foraging behaviour of ants is often affected by temperature. In general, chemically recruited ants prefer to eat at temperatures lower than those that do not [50]. As a consequence, increased temperature results in pheromone decay changing the trail following action which is disadvantageous to the activity of ant feeding [51]. Hymenopteran parasitoids and small predators sometimes have a negative impact on rising temperatures. Ex: At 40°C BPH is 17 times more tolerant than its natural enemies *Cyrtorhinus lividipennis* and spider, *Pardosa pseudoannulata* [52].
