ARTHROPOD PREDATORS AND INSECT PEST CONTROL A CASE STUDY MARKURDI BENUE STATE

CHAPTER TWO

LITERATURE REVIEW

CONCEPTUAL FRAMEWORK

2.0 Insect Pests

The concise Oxford dictionary of the English language define pest as a troublesome or destructive person, or things. Williams [1947]state that an insect pest is any pest in the wrong place.

The classification of an insect as a pest is a subjective one based on its potential damage to human purposes or natural habitats and eco-system. Insect pests are said to be able to kill agricultural crops, ornamental plants etc. They can also consume and damage harvested food and also cause illness or unproductively in agricultural animals e.g. Cattle and vector as larvae while they may be pollinators in adulthood.

Some insects that are considered as pests are actually more beneficial than pestiferous for example wasps predate or parasitize many insects. An insect pest may cause injury which may be physical (bites and stings)or medical (causing diseases or illness) or economic (monetary lose of goods or properties). Injury may arise directly from the pest itself or may develop indirectly as a result of the actions or behavior of the pest. Insect pest affect us in one way or the other by the following ways:

1. They are an annoyance or nuisance e.g. cockroaches
2. They endanger human health or safety
3. They threaten the welfare of useful plants or domestic animals
4. They damage stored products or structural materials.

Although insect pest attract the most attention many insects are beneficial to the environment and to humans. Some insect like wasps, bees, butterflies and ants pollinate flowering plants. Insect pests can be controlled by the use of pesticides, sterilization, destruction of infected plant, traps, hunting, field burning, poisoned bait and biological control.

Insect can cause damage directly by their feeding or making shelters or indirectly by other means. Direct method include chewing of plants e.g. grasshoppers caterpillars, root chewing beetle larvae and piercing ant sucking which is the direct removal of plants sap or animal blood e.g. aphids, mites, bed bugs, lice, vegetable bugs e.t.c. while the indirect method can be through vectors e.g. plants viruses and bacteria transmitted via aphids and leafhoppers, malaria e.t.c.

Arthropod Predators

Arthropod predators are mainly free living species that consume a large number of prey during their life time. Insect predators can be found throughout plants, including the parts below ground, as well as in nearby shrubs and trees. Some predators are specialized in their choice of prey, others are generalists. Some are extremely useful natural enemies of insect pests.

Insect predators can be found in almost all agricultural and natural habitats.

Predators are organisms that kill and feed on prey and they are mainly free living species that directly consume a large number of prey during their whole life time. They are generally larger than their prey. The eggs are laid in the vanity of the prey and upon hatching from the egg, predators nymph or larvae actively seek out capture, kill and consume prey. Predators are insects and their relatives that consume several prey over the course of their development but some are more effective at controlling pests than others. Some species may play an important role in the suppression of some pests while others may provide good late season control but appear too late to suppress the early season pest population. Many beneficial species may have only a minor impact by themselves but contribute to overall pest mortality. Some common arthropod predators include true bugs, lacewings, wasps, predatory mites praying mantid, spider, damsel bugs, syrphid fly larvae etc.

Arthropod predators may be categorized based on their feeding mechanism.

1. Those with chewing mouthparts which simply chew up and swallow their victims. This includes lady beetles, praying mantids and ground beetles.
2. Those with piercing and sucking mouth parts which stick the mouth part into the prey and suck out the body contents. These predators often have powerful toxins and digestive enzymes that immobilize the prey. This group includes the lacewing larvae, syrphid larvae etc.

However arthropod predators are important in keeping insect pests in check and help to control the population of these pests

Characteristic Of Arthropod Predators

The characteristics of arthropod predators include

1. The adults and immature are often generalists rather than specialists.
2. They are generally large than their prey
3. They attack immature and adult prey
4. They kill or consume may prey
5. They destroy large numbers of prey quickly and thus their spectacular successes are often noticed.

Types Of Arthropod Predators

Lady Beetles

These are commonly called lady bugs. They can be recognised by their dome shape and they are often brightly coloured, often spotted. These colours are highly variable and includes orange, black or yellow. Lady beetles are the first beneficial insects that most people learn to recognise. There are hundreds of lady beetles species but practically all species share the traits of being predacious as both larvae and adult except for the Mexican bean beetle which is an important pest of soyabeans in some regions of the country.

The adult female beetle lays groups of 10-50 football shaped eggs usually on upper leaf surfaced or twigs. The eggs hatch into spiry, black and orange, alligator like larvae. Some beetle larvae that feed on mealy bugs have a white, waxy covering (similar to that of mealy bugs). After feeding the larvae, pupate usually on the underside of the leaf near their prey and emerge as adults. Lady beetles spend the winter as adults in protected areas and can live for 11 months or longer, some as longs as two to three years.

PREY: Lady beetles are heavy feeders both as larvae and adult. Most lady beetles seem to feed preferentially on aplids when they are present but they will also feed on caterpillar eggs and small larvae as well as mites and white flies. However, when an aphid population crashes due to an ant break of fungal disease, lady beetles are forced to pursue other food such as caterpillar eggs and small larvae. In cotton field where this occurs, lady beetles may aid in suppressing tobacco budworm and boll worm population for a week or two after the applied population crashes. Adults may then leave in search of better food but the wingless larvae do not have this option.

PLATE 1: Showing lady beetle

SOURCE: New, T.R. 1991

Lace Wings

These are most abundant in cotton fields and they are one factor that helps slow the overall population of the growth of cotton aphids. They lay their eggs at the end of long stalks preasumbly to protect them from ants. Lace wings are of two types, the brown lacewing and green lacewing. They are common in cotton fields during summer especially at times when aphids are or were recently numerous. They are slander insects with golden eye, long antennae and large transparent wings but the green lacewings are smaller than the brown lacewings and they are brown in colour with wings less transparent because they are covered with small brown hairs.

PREY: The larvae of both species feed heavily on aphid and white flies as well as on moth eggs and small caterpillars. The larvae of green lacewing are called “aphid lions” because they attack and consume large numbers of aphids, mites, lacebugs and other small insects. The adult of green lacewing are not predatory but that of brown lacewing are predatory. Pollen, nectar and even honey due sustain the general non predacious adults of green lacewing. As with lady beetles, they help control tobacco bollworm and budworm.

Praying Mantids

This large, highly distinctive insect is tan, green or grey with bulging eyes on the side of his heads. A distinctive feature is its enlarged pairs of legs, which are held out in front of its body as though it were praying. The female deposit a tan, bubbly egg mass on branches near the end of the summer and this egg mass contain over 200eggs. Mantids have one generation per year it undergoes incomplete metamorphosis.

Prey: Praying mantids feed on flies, aphids, moths, butterflies and many other insects. They catch their prey with their strong, barbed front legs. Or they also lie in wait with the front legs on an upraised position. They intently watch and stalk their prey. Mantids grasping response is incredibly rapid.

PLATE 2: Showing praying mantid

SOURCE: M.J. Shirley. 1999.

Syrphid Flies

These can also be called hover flies or flower flies. They are non biting and non stinging flies that closely resemble wasps and bees as they are often coloured similarly with alternating stripes of yellow and black across the abdomen. The larvae are sometimes mistaken for tiny slugs and are usually found in the midst of aphid colonies. This larvae also deposit tar-like excrement around the feeding site. Although these larvae are specialized predators or aphids but they are not usually present in sufficient numbers to control aphid populations by themselves but they are a component of the natural enemy complex that helps keep pest population below damaging levels.

Prey: The larvae feed primarily on aphids and they are capable of consuming over 400 aphids before pupating. However, they also feed on thrips, white flies, small insects and will also feed on a wide array of pests including plant bugs and various caterpillar pests.

Damsel bugs:

These are found on the soil surface, in leaf litter or near the base of plants. They have a piercing-sucking mouth parts for piercing the body of their prey and sucking out the contents. Damsel bugs have slender bodies and a dark triangle at the base of their wings. The adults are typically found on vegetation and ground cover. The nymph resembles adult but lack fully developed wings.

Prey: They feed on small, soft-bodied insects such as aphids, thrips, leafhoppers and spider mites and this is done by the immature and adult damsel bugs.

Ground Beetles

These are nocturnal hunters seeking concealed refuge during the day. Various species of are recognized, some are green, yellow or arrange in colour. Their bodies are usually flattered with grooves or rows of puncture running down the wing covers. They are usually a bit longer than wide, have long legs and run fast. They also have large heads and are somewhat fairly.

Prey: They consume many other arthropods and small prey such as earthworms and snails. Some ground beetles can also feed on decaying matter from during white others may be omnivores feeding on both plants and animals.

Spiders

Spiders have no antennae and two body parts: the cephalothorax, containing the eight legs, eyes, and mouth; and the abdomen, containing the digestive organs, genitals, and spinnerets. Spiders are an incredibly diverse group with roughly 3,000 described species.All spiders are predators, and most feed on insects caught in a web. Others, such as jumping spiders and wolf spiders, are active hunters relying on excellent vision to kill their prey. Crab spiders, another commonly encountered group, ambush their prey. A recent study indicates that spiders are often the most abundant predators, as a group, on a wide range of plant material in the home landscape. Batra, S.W.T. (1982).

PLATE 3: Showing a crab spider

SOURCE: Begon, M.1986

Pests And Pest Status

All approaches for handling pests begin with the concept of a pest. The designation of a species as a pest is entirely anthropocentric and does not directly relate to any intrinsic characteristic of a species. Pests are those species that humans identify as impairing human welfare, property, or activities (Pedigo, 1989). Usually, the designation of a species as a pest and an assessment of its importance reflect both what harm individual pests do and how many of the pests are present. Thus, a consideration of insect activities and insect densities (numbers per unit area) are important in recognizing insect pest species. Because insect numbers are subject to change (and also insect activities, though to a much lesser extent), a species may be regarded as a pest under one set of circumstances and not under another. A more formal system for recognizing pest species and their importance involves the idea of pest status.

Pest status is a ranking of a pest species relative to the potential economic impact of that species (Pedigo, 1989; Stern et al., 1959). In a seminal paper, Stern et al. (1959) defined both pest status and an array of other terms and concepts that form the foundation of modern pest management. They proposed different rankings of pests, as severe, perennial, occasional, and subeconomic, based on a hypothetical average population level of a species (termed the general equilibrium position) and its relationship to the economic injury level (EIL), a cost-benefit criterion for evaluating the impact of pests. Perennial and severe pests cause the most serious and difficult problems for pest management and are often referred to as key pests (Pedigo, 1989). We discuss the EIL in more detail later; at this point, the key issue to highlight is that Stern et al. (1959) placed identification of pest status on a formal basis through an evaluation of economic impact of pest species. The EIL indicates where the economic costs of pest activities equal the economic benefits of taking action against pests. The concept of the EIL is important because it provides a mechanism for evaluating pest impact and implies that not all levels of pests require management. In establishing an economic and ecological rationale for addressing pest problems, Stern et al. (1959) provided the framework for a new paradigm for pest control. Although their failure to completely define certain concepts delayed the application of many of their ideas for more than a decade, these omissions do not diminish the impact of their work. Many workers built upon their ideas, ultimately developing modern concepts of pest management. Unfortunately, those concepts are not universally accepted.

Preventing Pest Damage

Pest management differs from previous approaches to pest control because it focuses on tolerating pests. Through the EIL, tolerance is expressed in economic terms based on economic impacts from pest activities and economic costs associated with management action. As a fundamental objective, pest management programs seek to reduce the impact of pests to tolerable levels, not to the lowest levels obtainable Perkins (1982), in his important history of pest management, argues that the postinsecticide era was dominated by conflicting philosophies of total population management, an approach calling for areawide or regionwide pest population suppression, and pest management, an approach focusing on tolerating pest populations. Perkins’ (1982) total population management refers to efforts by E. F. Knipling and other scientists to regulate or eradicate pest populations.

However, we believe the underlying philosophical conflict between pest management and alternatives is more fundamental than those that Perkins (1982) highlights. Specifically, there are essential differences between what we identify as management and control philosophies. The control philosophy represents a viewpoint that ignores or minimizes the importance of tolerating pests and looks instead to purposeful regulation of pest populations. Some control approaches may consider economics in taking action, particularly in emphasizing economic risks from pest populations. Others may not. Control is based on the premise that we can and should regulate pest populations to whatever level is desirable, typically a very low level. At its extreme, the control philosophy is expressed in pest eradication efforts. In contrast, the management philosophy focuses on reducing pest impacts while tolerating some level of pests. Because tolerating pests is a fundamental issue for management, so is economics, as it directly relates to what is tolerable.

Although management programs may be directed to reduce pest population levels, efforts are not directed toward permanently regulating pest populations through continued human intervention. In choosing between these philosophies, it is important to recognize that management is based on ecological principles, whereas most control is not. Successful eradication of the screwworm [ Cochliomyia hominivorax (Coquerel)] from North America was based on ecological realities and represents the outstanding success in pest control (Knipling, 1979). Unfortunately, the more widespread legacy of control has been rampant pest resistance to pesticides resulting from pesticide overuse. Some applications of a control approach are appropriate, even in the context of pest management programs. For example, control efforts to eradicate an introduction of a new pest species are appropriate. However, such applications for control are very limited. Although pest management has become the predominant approach for handling pest problems, the conflict between control and management philosophies does persist. Many practioners continue to use pest control approaches. Similarly, much more research is directed toward developing pest control tactics than fundamental pest management tools. Control approaches often seem to offer magic bullets for pest problems, but it is a false promise given that their use is not sustainable. Unfortunately, the appeal of simple solutions to pest problems that control seems to promise is difficult to counter. For example, deployment of bioengineered genes for plant resistance to pests presently is based on notions of control rather than proper pest management, with the virtually certain prospect that such deployment approaches will encourage pest resistance (Funderburk and Higley, 1994).

Crop Tolerance To Arthropod Injury

Because tolerating pests is such an essential concept of pest management, it is important to define tolerance. In using the EIL to define what is tolerable, there is a strong emphasis on economic criteria. What is somewhat less obvious, but equally important, is the biological basis for tolerating pests-specifically, the relationship between pest activities and yield losses. These relationships vary based on a host of factors, including, but not limited to, pest densities. On a simple level, where the action of pests has little individual impact on marketable yield, more pests can be tolerated. Complexity arises as we try to quantify this relationship between pest numbers and yield and as we examine possible approaches for minimizing the impact of pests on yield. The nature of pest injury and physiological responses of crops to injury set the boundaries within which management actions are possible. Consequently, understanding the physiological responses of plants to pest injury is an essential undertaking for developing pest management programs. These responses to pest injury should be considered in the context of plant stress.

Fundamentally, pest management is one approach for avoiding or reducing the impact of biotic stress; it is a type of plant stress management. Although most emphasis on plant stress has focused on abiotic stressors, insects and other biotic agents are equally important as possible plant stressors. Unfortunately, plant stress from most biotic agents is poorly understood. Because plants integrate the effects of all types of stressors, predicting the impact of those stressors and developing approaches to mitigate that impact require comparable integration in our understanding of stress. Consequently, finding unifying concepts and terminology for examining plant stress is important in building a more comprehensive understanding of stress.

Higley et al. (1993) discuss some of the constraints to more unified understandings of plant stress and offer some new definitions for more encompassing views of stress and related parameters. They recognize plant stress as an adverse reaction to the effect of environmental factors, biotic and abiotic, and define stress as a departure from optimal physiological conditions. For example, a reduction in net photosynthesis is a stress that can be caused by insect feeding. Other important considerations are agents producing stress and plant responses to stress. Workers on biotic stress have long distinguished between injury, the action of a stressor on a plant, and damage, the plant’s response to injury (Tammes, 1961; Bardner and Fletcher, 1974; Pedigo er al., 1986). Modifying previous usage, Higley er al. (1993) formally define these terms as: injury-a stimulus producing an abnormal change in a physiological process; and damage-a measurable reduction in plant growth, development, or reproduction resulting from injury. Injury, stress, and damage are terms that provide a common language for addressing all types of stress. Moreover, they indicate the specific events associated with stress: stimulus, physiological change, and reaction. Injury is the specific stimulus producing stress. Stress is the deleterious alteration of one or more physiological processes. Damage is the measure of how stress impacts plant fitness; in agronomic terms, it is a measure of yield loss or quality.

Consequently, damage is especially useful as a practical expression of plant response to injury. Our understanding of arthropod injury and resulting stress and damage is poorly developed. Despite the importance of the topic, surprisingly few reviews of plant responses to arthropod injury are available. Bardner and Fletcher (1974), Fenemore (1982), Pedigo et al. (1986), and Welter (1989) reviewed aspects of plant response to arthropod injury. Although a large body of literature addresses insect-plant interactions, almost all of this work focuses on how plants affect insects rather than the reverse. Indeed, many workers have pointed out the need for additional research emphasis on plant responses to arthropod injury (e.g., Bardner and Fletcher, 1974; Boote, 198 1 ; Funderburk and Higley, 1994; Pedigo et al., 198 1, 1986; Wintersteen and Higley, 1993).

Plant Resistance to Arthropods

Plant resistance is one of the most effective tactics available in IPM, because management is achieved with little cost to the grower and without potential health risks and environmental contamination from pesticides. Plant resistance also is compatible with other management tactics, including biological management (Boethel and Eikenbary, 1986; Smith, 1989). Even partial resistance may be sufficiently effective in conjunction with cultural or biological management to reduce or avoid the need for therapeutic actions (Starks et al., 1972). Painter (195 1) provided the first comprehensive discussion of plant resistance to arthropods.

Russell (1978), Panda (1979), Maxwell and Jennings (1980), and Smith (1989) provide more recent overviews of the subject. Resistance to major pests of selected crops is reviewed by Khush and Brar (1991). Plant resistance is the use of genetically controlled plant defense mechanisms to regulate herbivore populations (Painter, 195 1 ; Smith, 1989). Pseudoresistance, which manipulates plant growth and development to evade arthropod attack (Smith, 1989), and plant associational resistance, which relies on intercropping to disrupt host-finding behavior by a pest (Risch et af., 1983), are discussed in the next section on cultural management. Resistant cultivars traditionally have been developed using natural resistance sources in the same or related plant species.

However, recent advances in plant molecular engineering have created a vast potential for artificially incorporating novel resistant mechanisms into plants. Agronomically acceptable engineered crops containing genes for production of the toxin derived from the entomopathogen Bacillus thuringiensis probably will be available in the near future. The mechanisms of plant resistance are antixenosis (nonpreference), antibiosis, and tolerance (Painter, 1951 ; Smith, 1989). Antixenosis operates by disrupting normal arthropod behavior, whereas antibiosis adversely affects a pest’s physiological processes, thereby impairing arthropod survival, growth, development, and behavior. Antixenosis and antibiosis involve both plant and arthropod characteristics. Tolerance is a plant response to injury where acceptable plant production (i.e., yield) is achieved in spite of injury by a pest. Plant breeders and entomologists have focused on developing crop cultivars that are resistant to key pests particularly when insecticidal tactics are costly or ineffective. Plant breeders typically have relied on antibiosis as the preferred mechanism for developing resistant cultivars, because antibiotic mechanisms generally are more stable and provide more complete suppression in the field. Furthermore, when antibiosis is conferred by one or a few dominant genes, selection usually can be done easily in the greenhouse or field.

Antibiosis can be mediated by toxic allelochemicals, such as various types of alkaloids, arthropod growth inhibitors, reduced plant nutrient levels that inhibit arthropod growth, plant hypersensitivity, and plant structural factors such as glandular trichomes that secrete allelochemicals or adhesive substances that inhibit pest movement. Twenty sources of antibiotic resistance have been identified in small grains to the Hessian fly, Mayetiola destructor (Say) (Patterson et af., 1992). All except two sources are conferred by single dominant genes, although the exact chemical basis for resistance is not known for any source. Virtually all field corn hybrids grown in the Midwest United States produce elevated levels of the allelochemical DIMBOA (2,4-dihydroxy-7-methoxy- 1,4-benzoxazin-3-0ne), which has antibiotic effects on European corn borer larvae during the whorl stage (Klun er al., 1967). Antixenotic resistance consists of plant morphological or chemical factors that reduce the attractiveness of a plant as a host, resulting in the selection of an alternate host (Smith, 1989). Specific defenses include presence or absence of trichomes and leaf surface waxes, increased thickness of plant tissue, and chemical repellents or feeding deterrents (Smith, 1989). Feeding by the potato leafhopper [Empoasca fabae (Harris)] is deterred by the presence of simple erect trichomes on leaves of soybean (Broersma et al., 1972) and potato (Solanurn tuberosum L.) (Taylor, 1956). Leaves with wax blooms stimulate some insects and deter other insects from feeding on some crucifer crops (Stoner, 1990). Chemically based antixenosis can result from the presence of a chemical deterrent such as saponins, cardiac glycosides, cucurbitacins, condensed tannins, isoflavones, and various alkaloids (Smith, 1989). Antixenosis often provides partial resistance and may be less effective when resistant cultivars are grown over large geographical acres.

EMPIRICAL STUDIES

Chhay et. al (2017) examined the necessity and economic viability of insecticide use for rice cultivation, and the multiple interactions between the populations of both insect pests and natural enemies in dry-season rice fields. The outcomes of calendar-based insecticide-sprayed and non-sprayed rice fields were compared at three provincial research stations in Cambodia in terms of rice growth, economic returns, damage caused by insect pests, and population dynamics of insect pests and arthropod natural enemies. The results showed that rice fields without insecticide application did not suffer significant damage by insect pests or by diseases and had similar yields to those treated with insecticide application in two provinces.

Although the occurrence of caseworm was observed in the third province, this was successfully controlled by an integrated pest management (IPM) treatment without using insecticides. Insufficient densities of natural enemies appeared to correlate with the caseworm outbreak in this location, whereas high densities of natural enemies relative to those of insect pests contributed to control potential pest expansion in the other two provinces. Natural enemy populations were significantly decreased by insecticide applications. Reduced insecticide input in the insecticide-free control and IPM plots resulted in higher net profits than those in insecticide-applied plots, except for plots in the region with a caseworm outbreak (insecticide-free). Overall, this study provides encouraging insight into cost effective and environmentally friendly pest management in Cambodian rice fields.

Adrien et. al (2010)carried out a review to expose which elements, from the field to the landscape scale, influence natural enemy populations and pest regulation. They present the principal effects of seminatural habitats, farming systems, and crop management on the abundance of insect pests and their biological control, with a view to evaluating their relative importance and identifying key elements that regulate natural pest control interactions. Because of the range of spatial and temporal scales experienced by these organisms, they advocated, in studies investigating trophic relations and biological pest control, a clear description of cropping systems and an explicit consideration of seminatural habitats and more generally of the surrounding landscape.