**3. Effect of different climate change factors on insect pest, plants and their interactions**

In agriculture, climate change can interfere in normal plant physiologies such as photosynthesis, respiration, transpiration, nutrient absorption, balance of minerals and exchange of ions etc. It may also intervene with the production of crops by altering the population and function of insect pests. Climate variables such as temperature, humidity, precipitation etc. are accountable for the growth, development and multiplication of organisms like insects, fungi, bacteria, virus etc. As with the changing climate, populations of pest are also expected to change. In addition, climate change is expected to fetch modifications in host plant resistance against insect pests. The resistance can be overcome by faster disease cycles and altered physiologies of insect pest. As global warming is caused by climate change, several insect species are affected in terms of their distribution, demography, and life history parameters. The response of an insect population to a swiftly changing

*Climate Change and Its Potential Impacts on Insect-Plant Interactions DOI: http://dx.doi.org/10.5772/intechopen.98203*

climate will be inconsistent when insects interact with different competitors, predators and parasitoids. This also affects overall food production systems that can be at critical risk due to the consequences of climate change [7]. These changes inflict consequences on human livelihood, including the rapid spread of pest and diseases of important crops. This has brought new challenges to agricultural sustainability.

### **3.1 Effect of temperature on insect pest and plants**

The global average temperature is expected to increase by at least 4°C by the end of the 21st century, due to the increased frequency and intensity of drought and heat waves [8]. Temperature has a strong effect on insect growth, survival and reproduction and enrols a major role in controlling the development and growth of their host plants. In addition, the development of plant secondary chemicals as well as the structural characteristics used to protect against herbivores are influenced by temperature. Thus, for both insects and plants, temperature has potentially significant consequences (**Figure 1**). Phytochemical and morphological changes in host plants are caused by changes in temperature. For example, at night temperatures of 17°C, the concentration of catecholic phenolics (chlorogenic acid and rutin) in tomatoes was significantly higher than at other temperatures [9]. Also, Rivero et al. [10] reported low polyphenol oxidase (PPO) activity of peroxidase (POX) at 35°C in tomatoes; it has been also reported that there is a substantial decrease in protease inhibitor activity in tomato at temperatures below 22°C [11]. At elevated temperatures, the thickness of leaf trichomes normally rises [12].

In alfalfa (*Medicago sativa*), the concentrations of plant secondary metabolites (sapogenins and saponins) were elevated at increased temperatures, suppressing the growth of caterpillar (*Spodoptera exigua*). By contrast, the Green-veined

**Figure 1.** *Effects of elevated CO2 and temperature on plant, insect and their interaction.*

butterfly, *Pieris napi* reacted to warming-mediated poor-quality foliage in Brassicaceae, by consuming significantly higher amounts of plant tissue [13]. However, when fed on oilseed rape plants subjected to different temperatures with nutritional quality variations, the production of aphids (*Myzus persicae* and *Brevicoryne brassicae*) was not affected [14]. Moreover, temperature-induced tobacco shifts (*Nicotiana tabacum*) have an impact on the tobacco hornworm, *Manduca sexta* that the normally accepted law of temperature size, which predicts an improved final mass of ectotherms (e.g. insects) at lower temperature, has been reversed [15].
