Climate change impacts pest populations in a variety of ways. Some of the most common effects include increased winter temperatures, warmer summer temperatures, and a reduction in cold temperature extremes.

In general, rising temperatures will enable existing pest species to grow faster and reproduce more frequently. This is especially true for insects with yearly life cycles.

1. Increased Temperature

Temperature plays a direct role in pest phenology, metabolism, development, movement, and survival. It also influences the relationships of pests with their host plants, natural enemies and the environment, and can alter population dynamics. The physiology of insects tends to increase with temperature rise, which is expected to lead to faster growth and fecundity, increased movement rates and colonization ability, and changes in population size and geographic range and inspection and evaluation of the infested area.

Temperature also impacts insect morphology. Warmer temperatures enable insects to reproduce at higher rates, resulting in an increased number of generations and increased damage to crops. In addition, warmer climate conditions can make it difficult for pests to avoid their predators, which leads to a loss of biological control and a rapid increase in populations.

The effects of temperature rise on pests are exacerbated when they occur in combination with other climatic factors such as milder winters, warmer spring weather and changeable precipitation patterns. These climate shifts can create new ecological niches that allow crop pests to thrive and expand their geographic ranges.

For example, aphids can quickly grow and reproduce in a variety of different environments. However, they are typically limited in their range by the availability of a specific pheromone that serves as an alarm signal for their natural predators. This pheromone is triggered by cold temperatures and is a key factor in the control of aphid populations.

Climate change will likely affect the ability of natural predators to detect this signal, meaning that aphids may be able to continue their unchecked expansion. In this case, the increased numbers of aphids will cause serious crop damage without being adequately controlled by natural enemies, leading to an even greater threat to food production and human health.

A similar scenario occurs with cereal leaf beetles (Oulema melanopus), a major global pest of maize and wheat. Climate change causes the emergence of new habitats that provide suitable conditions for this pest, as well as changing the distribution of its predators and parasitoids [5]. Consequently, this change in environmental conditions makes the herbivorous beetle more successful at damaging crops.

2. Changes in Soil Moisture

The climate change that has been occurring over the past several decades has had a significant impact on the earth’s millions of insect species. This includes changes in the amount of precipitation, wind patterns, temperature and humidity. These changes also have a direct impact on the earth’s crops and their pest populations.

As the earth warms, pest populations can build up quickly. As they grow, their ability to consume plants and spread can be enhanced, leading to damage to our crops and food supply.

In addition, as temperatures increase, the ability of insects to survive in cooler regions may be reduced. This can lead to a “perfect storm” for pests in which they have an abundant source of food and no natural predators to prevent them from overwhelming and destroying our crops.

The impact of climate change on insect pests depends largely on temperature, which influences many different aspects of their biology. For example, higher maximum temperatures can reduce insect growth rates by lowering their metabolic rate, and increase the frequency and intensity of heat waves. In addition, higher winter minimum temperatures can favour the overwintering of invasive species and increase spring phenology, which can lead to a faster build up of pest populations.

As the climate changes, the relative importance of each of these factors will vary by insect species. For example, the effects of increased temperature will be much more severe for aboveground insect pests that spend most of their lives in the air than for those that live underground and feed on roots or soil. This is because aboveground insects are exposed to more extreme temperatures and higher variation in temperature, whereas ground-based insect pests are insulated by the thermal mass of the soil.

In addition, climatic changes can affect the interaction of insect pests with their natural enemies, such as parasitoids, herbivores and predators, through a number of mechanisms. These include a shift in the geographic range of habitats in which natural enemies can find suitable host plants, an alteration in their feeding preferences due to climate change, and the effect of temperature changes on the metabolisms of pests and their natural enemies.

3. Changes in Water Supply

Increasing temperatures can also cause changes in precipitation patterns and amounts. These changes can lead to more frequent and severe flooding and droughts, as well as changes in the quality of water supply sources. For example, frequent and heavy rainfall can result in the runoff of sediments, nutrients, pathogens, and other contaminants into bodies of water such as rivers, lakes, ponds, estuaries, and the ocean. This pollution can harm ecosystems and affect human health and water supplies. It can also increase the frequency of harmful algal blooms, which can kill fish and shellfish and make water unsafe for drinking.

Climate change can also affect the water supply of people living in rural and arid regions. For example, increasing temperature and shifting precipitation patterns can decrease the availability of freshwater, which is necessary for growing crops and sustaining livestock. This can also increase the costs of water supply, which can limit access to affordable and nutritious food.

Because of the complex and varied effects of climate change, pest responses to it are biome and habitat specific. In general, however, most climate change scenarios favor pest proliferation worldwide, with the exception of tropical regions.

In addition, a shift in temperature can decouple the synchronized population dynamics of insect pests and their natural enemies. For example, a study of the aphid-parasitoid wasp relationship showed that elevated temperatures increased aphid fecundity but reduced parasitism effectiveness [43].

Finally, climate change can impact crop pest populations through a range of other indirect mechanisms. For example, climate change can destabilize agricultural infrastructure and damage crops through increased droughts and floods. This can lead to decreased production, which can in turn increase prices and reduce food security for people around the world.

Several hundred million people would be at risk of hunger if average global temperatures rise more than 1.5°C above pre-industrial levels, according to a recent report from the UN Intergovernmental Panel on Climate Change (IPCC). Limiting global temperature increases to this level can avoid the most devastating impacts on human health and welfare and protect agriculture and ecosystems.

4. Changes in Predators

As climate warming leads to changes in plant growth and water supply, it can also affect predator populations. Predators are key to keeping pests in check, and a decrease in predators can lead to an increase in the size of the pest population. This can cause serious economic losses to crops and threaten human food security.

Scientists have been studying the effects of climate change on predator-prey relationships to determine the impact on both species. The results have been quite varied and have led to some surprises. For example, one study found that the size of a predator population was affected by its ability to subdue prey, rather than by the presence of other predators. The researchers concluded that a loss of predators could cause the pest population to grow out of control, and this would lead to increased damage to crops.

Another study examined the effect of rainfall on predator-prey relationships and found that a decrease in predators caused by drought can result in higher population levels of the pest. This is because the lack of predators means that the prey species can reproduce faster, resulting in an exponential increase in its population. This, in turn, leads to an increase in the number of eggs laid and a higher risk of infestation of crops by the pest.

This type of scenario is likely to occur in the future, as climate change leads to decreased predator numbers and increases in the size of the prey species. This can lead to increased crop damage and the need for more intensive pest control measures.

Moreover, climate change is also driving the expansion of some insect pests’ ranges. For instance, warm temperatures can allow prickly pear (Opuntia Mill) to thrive in new areas by boosting overwinter survival rates and increasing the number of generations per year.