The majority of humans are unwilling to coexist with organisms that compete for life’s essentials, aggravate, irritate, or disrupt their comfort, and harm their well-being or property. These organisms are commonly referred to as ‘pests’. The medical and veterinary industries manage the microorganisms that affect the internal functions of humans and animals, while the pest management industry deals with the rest. Urban pest management does not involve agricultural pests, instead, it involves pests that directly attack humans, invade structures, and eat stored food, fabrics, and other properties.
Insects have been very successful in exploiting the human environment, and their influence is noteworthy.
Beneficial Insects
Out of over a million described insect species, only less than 3% are considered pests. The continued supply of fruits, vegetables, flowers, and other plants is all thanks to pollinating insects. Some insects provide products like beeswax, silk, shellac, and honey. They also play an essential role in the food chain as they are food for many higher organisms such as birds, reptiles, and mammals. There are insects that parasitize pest insects, such as small wasps which are often used as biological control agents that can help drive the pest population down. Some have a scavenger habit that feeds on dead organic matter and animal droppings. Insects can also provide aesthetic pleasure like butterfly farms and preserved insect mounts.
Why are insects so successful?
Size
Insects come in different sizes from microscopic to as big as smaller mammals. Overall, they are smaller than most animals, which is considered an advantage because they can exploit many different habitats available.
A disadvantage of being so small in size in animals is that because of the ratio of body surface area to body volume, moisture is lost more easily than in larger animals. Conservation of moisture is important in any life form, and insects have a solution for this problem which is their body covering.
Rapid reproduction
Insects can reproduce very rapidly in a short amount of time and often quickly develop into reproductively mature adults. An example of this is the German cockroach, which can undergo four generations per year. A female German cockroach can lay several egg cases that each contain 30-40 offspring, a population in an undisturbed habitat can be extensive.
Most female insects lay large numbers of eggs on substrates that their young can feed on when they hatch. Most insects also undergo very short life cycles— these two factors favour adaptability.
Adaptability
High rates of sexual reproduction create a diverse genetic pool in large populations, enabling rapid adaptation to diverse environmental conditions. Adaptability is a crucial survival advantage, especially in a competition with humans for resources. A short life cycle ensures swift adaptation to changing conditions, preventing extinction.
Over millions of years, insects have evolved diverse mouthparts to suit various diets. Primitive chewing mouthparts, seen in insects like cockroaches and grasshoppers, have adapted over time to pierce plant or animal tissue for food. This specialization is evident in hemipterans like bedbugus, and siphonapterans or fleas.
The insect’s capability and tendency to adapt to various conditions and environments have resulted in changes to their developmental processes.
Higher insects undergo specialized development, with flies, beetles, fleas, and moths experiencing complete metamorphosis — a significant change in form as they grow. Different growth stages serve specific purposes: the larval stage focuses on consuming and building reserves for the pupal stage, where the pupa undergoes a remarkable metamorphosis inside a cocoon, resulting in the emergence of an adult beetle, moth, butterfly or flea with piercing-sucking mouthparts. The adult’s main role is to find a mate and contribute to the next generation. Feeding isn’t as important in this stage as it is in the larval stage, except for females, which require nutrients for egg production. Some adult insects such as mayflies and certain moths, never feed during their whole adult life because of their short life span.
Primitive insects such as cockroaches, experience minimal changes in their growth, perhaps acquiring wings and reproductive organs only upon reaching adulthood.
In recent times, due to their rapid life cycle and extensive genetic variability, numerous insect strains have evolved resistance to different pesticides, adapting to chemical control measures.
Body covering
Insects unlike higher animals have an exoskeleton, which is like a skeleton outside of the body. The exoskeleton is made of a polysaccharide carbohydrate called chitin. Chitin can vary in flexibility and is shed periodically during ecdysis for the insect to grow. The exoskeleton not only covers and protects the body from desiccation but it is also a surface for muscle attachment for movement.
Other Protection
Aside from protective body covering, insects have developed many different protective adaptations against predators. Some caterpillars have spines, bristles, urticating hairs, or camouflage that can protect them from predators as they are exposed when they feed on foliage.
There are insects with a “fracture line” in each appendage that allows them to easily break off their appendage if caught by a predator — this is called autotomy or dropping. Autotomy is common in long-legged insects like crane flies, stick insects and grasshoppers. Generally, losing an appendage is only a minor disability, in fact, stick insects can regenerate their missing appendages after several moults.
Some insects play dead to avoid predation, this phenomenon is called thanatosis, more commonly known as feign death. Certain caterpillars, lady beetles, weevils, giant water bugs, robber flies, and the genus Cryptoglossa or death-feigning beetles are known to exhibit this behaviour.
Many insects use chemicals to defend themselves against their enemies. Some insects make their own toxins in their bodies, and in some cases, the chemicals are acquired from host plants. When threatened, the chemical compounds may be released on the surface of the body, into the air as a repellent, or sprayed directly at the enemy.
Flight
Insects were the first animals to evolve flight and this has definitely aided their success in exploiting the human habitat. Although wingless insects like fleas and bedbugs are still successful in dispersing, the ability of adult insects to fly cannot be overemphasized as a reason why they are able to disperse widely and escape unfavourable conditions.
Insects and Disease Transmission
There are two methods by which insects transmit pathogens:
Biological or cyclic transmission
The pathogenic organism is transported within the animal’s body, where it multiplies, reproduces, or undergoes stages of its life cycle before it is typically transmitted to a new host through biting to obtain a blood meal. Examples of this transmission method are malaria, dengue fever, and encephalitis.
Mechanical or passive transmission
Insects pick up pathogens when they make physical contact with or feed on contaminated water, garbage, faeces, and other wastes. The pathogens can be transmitted passively via excrement, regurgitation, or by carrying them externally on their body to food and surfaces. Diseases transmitted passively include dysentery, hepatitis, gastroenteritis, and Salmonella.