Introduction

In recent decades, elevated awareness of the impacts of pesticide use on the climate and human health have brought about efforts to decrease reliance on chemical controls. Many nations have instituted more stringent regulation of pesticide manufacture, registration and use, subsequently increasing the expense, and decreasing the availability of these tools. In many cases, the actual bugs have indicated the requirement for change, with pesticide resistance now a typical reality in many weeds, insects and diseases. The requirement for alternatives to pesticides is clear, yet where will these arrangements come from? A recent report by the U. S. Congress, Office of Innovation Assessment (U. S. Congress, OTA 1995) indicates that biologically based advances, for example, biological control could be more generally used to tackle pressing requirements in bug management.

The utilization of natural foes to decrease the impacts of irritations has a long history. The ancient Chinese, observing that ants were viable predators of many citrus bugs, augmented their populations by taking their homes from surrounding habitats and placing them into their orchards. Today’s insectaries and air-cargo conveyance of natural foes across the nation or around the world are simply current adaptations of these original ideas. In this article we will examine approaches to biological control and applications of these approaches in current vermin management. While the principles of biological control can be applied against various vermin organisms (for example weeds, plant pathogens, vertebrates and insects), we will limit our conversation to the utilization of biological control of insects, primarily using different insects as natural foes.

Approaches to Biological Control

There are three general approaches to biological control; importation, augmentation and conservation of natural adversaries. Each of these strategies can be utilized either alone or in combination in a biological control program.

1.Importation

Importation of natural foes, at times alluded to as classical biological control, is utilized when a vermin of fascinating origin is the target of the biocontrol program. Irritations are constantly being imported into nations where they are not native, either accidentally, or now and again, intentionally. Many of these introductions don’t bring about establishment or on the off chance that they do, the organism may not become bothers. Be that as it may, it is entirely expected for a portion of these introduced organisms to become bothers, because of a lack of natural foes to smother their populations. In these cases, importation of natural foes can be profoundly viable (Caltagirone 1981).

When the nation of origin of the irritation is determined, exploration in the native area can be led to search for promising natural foes. In the event that such adversaries are distinguished, they may be evaluated for potential impact on the nuisance organism in the native nation or alternatively imported into the new country for additional review. Natural adversaries are imported into the US just under permit by the US Department of Agriculture. They should initially be placed in quarantine for one or more generations to be certain that no undesirable species are accidentally imported (diseases, hyperparasitoids and so on.). Additional permits are expected for interstate shipment and field release.

Biological control of the alfalfa weevil, Hypera postica (Gyllenhall) is an example of a fruitful program using importation of natural foes (Bryan et al. 1993). The alfalfa weevil, a native of Europe, was originally recognized in the US in Utah in 1904. A subsequent introduction was recognized on the East coast in 1951. By 1970, the weevil had spread to all 48 bordering states and become a serious bug of alfalfa. Some importation’s of natural foes began as early as 1911, in any case, a major program aimed at biological control of the weevil was initiated in 1957. In this program, USDA ARS faculty directed foreign exploration in Europe resulting in the eventual importation of 12 parasitoid species. Six of these species became established and are credited with contributing to the decrease in the weevil’s bug status in the eastern US (Day 1981).

2.Augmentation

Augmentation is the immediate manipulation of natural adversaries to increase their adequacy. This can be accomplished by one, or both, of two general techniques: mass creation and intermittent colonization; or hereditary enhancement of natural adversaries. The most normally utilized of these approaches is the first, wherein natural adversaries are created in insectaries, then, at that point, released either inoculatively or inundatively. For example, in areas where a particular natural foe cannot overwinter, an inoculative release each spring may allow the population to establish and adequately control a vermin. Inundative releases involve the release of large quantities of a natural foe to such an extent that their population totally overpowers that of the irritation. Augmentation is utilized where populations of a natural foe are absent or cannot answer to the vermin population. Therefore, augmentation usually doesn’t give permanent concealment of bugs, as may happen with importation or conservation techniques.

An example of the inoculative release technique is the utilization of the parasitoid wasp, Encarsia formosa Gahan, to stifle populations of the nursery whitefly, Trialeurodes vaporariorum (Westwood), (Hussey and Degrees 1985, Parrella 1990). The nursery whitefly is a ubiquitous irritation of vegetable and floriculture crops that is notoriously hard to manage, even with pesticides. Releases of relatively low densities (typically 0.25 to 2 for every plant, depending on the harvest) of E. formosa immediately after the primary whiteflies are recognized on a nursery yield can really keep populations from developing to damaging levels. In any case, releases ought to be made within the setting of an integrated yield management program that takes into account the low tolerance of the parasitoids to pesticides.

3.Conservation

In any biological control effort, conservation of natural foes is a critical part. This involves identifying the factor(s) which may limit the viability of a particular natural foe and modifying them to increase the adequacy of the beneficial species. In general, conservation of natural foes involves either, reducing factors which interfere with natural adversaries or providing resources that natural foes need in their current circumstance.

Many factors can interfere with the viability of a natural foe. Pesticide applications may straightforwardly kill natural foes or have indirect impacts through decrease in the numbers or availability of hosts. Various cultural practices, for example, tillage or burning of harvest trash can kill natural adversaries or make the yield habitat unsuitable. In orchards, repeated tillage may create dust deposits on leaves, killing small predators and parasites and causing increases in certain insect and mite bothers. In one review, occasional washing of citrus tree foliage brought about increased biological control of California red scale, Aonidiella aurantii (Maskell) due to increased parasitoid effectiveness (Debach and Rosen 1991). Finally, have plant impacts, for example, chemical safeguards which are harmful to natural foes yet to which the bug is adapted, can diminish the viability of biological control. A few irritations are able to sequester toxic parts of their host plant and use them as guard against their own foes. In different cases, physical characteristics of the host plant like leaf hairiness, may diminish the ability of the natural foe to find and attack has.

Ensuring that the ecological necessities of the natural adversary are met in the cropping climate is the other major means of conserving natural foes. To be successful, natural adversaries may require access to; alternate hosts, adult food resources, overwintering habitats, constant food supply, and appropriate microclimates (Rabb et al. 1976). In a classic example, Doutt and Nakata (1973) determined that Anagrus epos Girault, principal parasitoid of the grape leafhopper, Erythroneura elegantula Osborne in California grape vineyards required an alternate host for overwintering. This host, another leafhopper, just overwintered on blackberry foliage in riparian areas, frequently quite distant from the vineyards. Vineyards near natural blackberry stands experienced earlier colonization by the parasitoid in the spring and better biological control. Wilson et al. (1989) found that French prune trees which harbor another overwintering host, could be planted upwind of vineyards and actually conserve Anagrus epos.

Current Applications of Biological Control

Biological control is an exciting science because it constantly incorporates new information and procedures. In this part we will illustrate several ways wherein revered approaches to biological control are being adapted to address today’s nuisance management difficulties.

Modern Approaches in Augmentation of Natural Foes

Because most augmentation involves mass-creation and intermittent colonization of natural adversaries, this sort of biological control has fit commercial turn of events. There are many biological control items available commercially for many vermin invertebrates, vertebrates, weeds, and plant pathogens (Anonymous 1995).

The practice of augmentation varies from importation and conservation in that making permanent changes in an agroecosystem to further develop biological control isn’t the primary goal. Rather, augmentation generally tries to adapt natural adversaries to fit into existing creation frameworks. For example, societies of the predatory mite, Metaseiulus occidentalis (Nesbitt) were laboratory-chosen for resistance to pesticides usually utilized in an integrated mite management program in California almond orchards (Hoy 1985). This program has saved producers $24 to $44 per acre each year in diminished pesticide use and yield misfortune (Headley and Hoy 1987). Hereditary improvement of several predators and parasitoids has been accomplished with traditional choice techniques (Hoy 1992), and appears conceivable with recombinant DNA innovation.

A superb example of an augmentative practice than has been effectively adapted to a wide variety of agricultural frameworks is the inundative release of Trichogramma wasps. These minute endoparasitoids of insect eggs are released in yields or forests in large numbers (up to several million/ha) coordinated to the presence of irritation eggs. Trichogramma are the most broadly augmented types of natural foe, having been mass-delivered and field released for almost 70 years in biological control efforts. Worldwide, north of 32 million ha of agricultural yields and forests are treated annually with Trichogramma spp. in 19 nations, for the most part in China and republics of the former Soviet Association (Li 1994).

In China, agricultural creation and nuisance management frameworks capitalize on low labor costs, and generally follow exceptionally innovative yet technologically simple cycles. For example, Trichogramma spp. that are inundatively released to smother sugarcane borer, Chilo spp., populations in sugarcane are shielded from rain and predators inside development packets. Insectary-reared parasitized eggs are wrapped in segments of leaves which are then sneaked past hand over blades of sugarcane. Most Trichogramma creation in China takes place in facilities producing material for a localized area. These facilities range from outside insectaries to mechanized facilities that are leading the world being developed of artificial host eggs.

One of the barriers to more extensive implementation of biological control in western agriculture has been socio-financial matters (van Lenteren 1990). In current large-scale creation agricultural frameworks, a premium is placed on effectiveness and economy of scale. Whole support industries have created around the application of agrichemicals, including application gear manufacturing, circulation and sales, as well as application administrations. In order for biological control items to not be at chances with these industries, and to contend emphatically with pesticides, they ought to have many of the same characteristics. Ideally, they ought to be as compelling as pesticides, have residual activity, be easy to utilize, and they ought to have the capacity to be applied rapidly on a large scale with conventional application hardware.

In Western Europe, almost two decades of intensive research brought about the commercial marketing of three items utilizing the European native, Trichogramma brassicae Bezdenko, to stifle the European corn borer, Ostrina nubilalis Hübner, in corn fields (Bigler et al. 1989). These items are annually applied to approximately 7,000 ha in each of Switzerland and Germany, 150 ha in Austria, and 15,000 ha in France. All three items are based on manufactured plastic or paper packets intended to give assurance to the wasps against weather limits and predation until rise in the field.

As in the Chinese example above, European Trichogramma items are for the most part applied to trim fields the hard way. One special case is the item called, Trichocaps which can be broadcast either the hard way or via aircraft using conventional application gear. Trichocaps packets are actually empty walnut-shaped cardboard capsules (2 cm. diam.) that each contain approximately 500 parasitized Mediterranean flour moth, Ephestia kuehniella Zwolfer, eggs (Kabiri et al. 1990). Developing Trichogramma inside capsules are induced into an overwintering (diapause) state in the insectary, then stored in refrigerated conditions for as long as nine months without loss of quality. This framework allows for creation of item during winter months, then conveyance to cultivators when required in the late spring.

Once eliminated from cold storage, Trichogramma inside the capsules will begin advancement and begin development approximately 100 Celsius degree days later. This ‘reactivation’ cycle can be manipulated so that capsules containing Trichogramma at various developmental stages can be applied to fields at the same time, extending the rise time of parasitoids and increasing the ‘residual’ activity of a single application to approximately multi week. Planning and preparation of the item for application is finished by the company with the goal that cultivators are just liable for applying the item to edit fields.

Cooperative research throughout the course of recent years (between BIOTOP, Trailblazer Hey Reproduced Intl., BASF, Univ. of Illinois, Iowa State University, Michigan State University, Purdue University, and Vermin Management Co. of Nebraska) has brought about fruitful commercial-scale pilot testing of this technique in North America on seed corn and field corn creation frameworks (Orr 1993, Orr et al. unpublished data). This strategy currently has the potential for immediate commercial implementation in North America.

Landscape Ecology and the Conservation of Natural Enemies

The investigation of disturbance and its consequences for community dynamics and the development of the discipline of landscape environment are impacting the way we think about the conservation of natural foes. Throughout recent years, environmentalists have come to perceive the central job that disturbance plays in the structuring of ecological communities (Pickett and White 1985, Reice 1994). While the most profoundly upset terrestrial environments may have one disturbance occasion like clockwork (for example fire in grasslands), many agricultural biological systems experience numerous occasions per growing season (plowing, planting, supplement and pesticide applications, cultivation and harvest). According to an ecological point of view, the results are predictable (Odum 1985). Exceptionally upset frameworks exhibit decreased species diversity and shortened pecking orders, resulting in the couple of all around adapted species (for example bugs) having not many natural adversaries to stifle their populations. This expects that additional disturbance occasions be initiated (for example pesticide applications) which, while controlling the initial negative symptom, may precipitate its reoccurrence.

Current frameworks of yield creation also shape the physical construction of our agricultural landscapes (Forman and Godron 1986). With increased reliance on mechanization and pesticides, diversity in farmlands has rapidly disappeared and the impacts on natural adversaries are simply now beginning to be understood (Ryszkowski et al. 1993). In general, increased habitat fragmentation, isolation and decreased landscape structural complexity will quite often destabilize the biotic interactions which serve to regulate natural biological systems (Kruess and Tscharntke 1994, Robinson et al. 1992).

The goal of an ecological approach to conservation biological control is to adjust the intensity and recurrence of disturbance to the point where natural adversaries can work really. This should happen at field, farm and larger landscape-levels. Within fields, modification of tillage intensity and recurrence (decreased tillage or no-tillage) can leave more plant buildup on the dirt surface and have a positive impact on predators (ground insects and bugs). Intercropping can also adjust the microclimate of harvest fields making them more favorable for parasitoids.

At the farm level, the presence and dispersion of non-crop habitats can every now and again be critical to natural foe survival. Eriborus terebrans (Gravenhorst) is a wasp which parasitizes European corn borer larvae. Female Eriborus require moderate temperatures (<90° F) and a source of sugar (nectar of flowering plants or aphid honeydew). Neither of these conditions is met in a conventionally managed corn field. Therefore, wasps look for more protected locations in lush fencerows and woodlots where they find diminished temperatures, higher relative humidity and abundant sources of adult food. European corn borer larvae in corn field edges near these sorts of habitats are parasitized at a few times the rate of those in field interiors (up to 40%) (Landis and Haas 1992). Ebb and flow research is examining the potential of modifying corn creation frameworks by creation of natural foe resource habitats to give critical resources and increase natural control of European corn borers. Intercrops, strip crops, as well as modification of grass waterways, shelterbelts, cradle and riparian zones are promising methods.

Finally, at the landscape-level, the physical construction of agricultural creation frameworks can also influence bug and natural foe diversity and abundance. In a review contrasting simple versus mosaic landscapes, Ryszkowski et al. (1993) presumed that natural foes are more subject to asylum habitats than are nuisances and the greater abundance of these shelters in the mosaic landscapes brought about their higher diversity, abundance and ability to answer prey numbers. Marino and Landis (in press) examined parasitism of genuine armyworm, Pseudaletia unipuncta (Haworth), in structurally-complex versus simple agricultural landscapes. Overall parasitism in the mind boggling sites was more than multiple times higher than in the simple sites (13.1% versus 3.4%). Contrasts were largely attributable to one wasp animal varieties, the braconid, Meterous communis (Cresson) which was far more abundant in complex sites. They theorized that abundance and proximity of favored habitats for alternate hosts of M. communis may account for the observed contrasts.

In the past, conservation was typically attempted each species in turn, concentrating on meeting the necessities of what was considered the main natural foe in a particular framework. While this will continue to be an enormously valuable approach, it presently appears to be conceivable that basic ecological theory could inform the plan and management of landscapes to conserve and enhance the viability of whole communities of natural enemie

Summary

Importation, augmentation and conservation of natural foes constitute the three basic approaches to biological control of insects. Explicit strategies within these approaches are constantly being created and adapted to meet the changing requirements of irritation management. Enhancements in rearing and release methods and hereditary improvement of natural foes have brought about more powerful augmentation programs. Application of new ecological theory is transforming the way we check out at conservation of natural adversaries. Continued refinement and adaptation of biological control approaches and applications are necessary on the off chance that the maximum capacity of this biologically based bug management strategy is to be satisfied.