Biological control how does it work

Podisus maculiventris preferentially feeds on lepidopteran larvae, whereas H. Such differential predation on particular stages of the same prey may lead to complementarity among predators, and ultimately enhance biological control. Here, we conducted field and laboratory experiments to evaluate how landscape composition influenced the effectiveness of augmentative biocontrol of lepidopteran pests by P.

Specifically, we asked: 1. Does augmentative biocontrol effectively enhance pest control and reduce plant damage? How does the interaction between landscape composition and enemy augmentation influence pest suppression?

We experimentally addressed these questions by releasing predators in cabbage fields situated in landscapes of varying complexity and evaluating whether predator augmentation suppressed pest populations to a greater extent than resident natural enemies acting alone. We further explored potential mechanisms responsible for our field results by evaluating the independent and combined effect of P. Relationships between the abundance of naturally occurring enemies and predation on sentinel eggs, predation on sentinel larvae, natural incidence of lepidopteran larvae, and plant damage.

All response variables were square-root transformed. The natural incidence of P. However, there was a positive relationship between the abundance of P. Augmentative releases of predators led to higher larval predation, lower plant damage, and higher crop biomass than the non-augmented control Fig.

A positive effect size indicates that the mean of the predator release treatment is larger than the mean of control treatment, while a negative effect size indicates a higher control mean.

Local effects of predator releases on larval predation were influenced by the composition of the surrounding landscape Fig. While caterpillar abundance and plant damage were significantly lower in the predator release treatment relative to the control in structurally complex landscapes i.

Crop biomass was also similarly affected by landscape composition with greater biomass in predator release treatments relative to control plots in complex landscapes, but in simple landscapes the opposite trend was observed Fig.

The effect of augmentative releases of predators on a lepidopteran larval abundance, b plant damage, and c crop biomass in landscapes of varying complexity. Predicted responses for the control solid lines and augmentative releases dashed lines treatments are calculated from the set of best supported linear mixed-effects models lme4. In the top Figures a — c every point represents the mean treatment value in a given experimental plot for a given sampling period i.

The bottom figs. A positive effect size indicates that the mean of the predator plots is larger than the mean of control plots, while a negative effect size indicates a higher control mean. Pairwise comparisons were individually calculated at even intervals across the landscape complexity gradient. Summary statistics of the LMER models used to estimate marginal means and confidence intervals are available in Table 1. As a result, larval predation was consistently higher in predator release plots irrespective of the landscape context Fig.

Predator releases increased egg predation in complex landscapes, but had no effect in simple landscapes Fig. The effect of augmentative releases of predators on a predation on sentinel larvae, and b predation on sentinel eggs in landscapes of varying complexity.

In the top Figures a and b every point represents the mean treatment value in a given experimental plot for a given sampling period i. A positive effect size indicates greater predation rates in predator compared to control plots, while a negative effect size indicates lower predation rates in predator plots. Landscape composition also had strong effects on resident natural enemy abundance. Predator releases reduced the abundance of foliar-foraging predators in simple landscapes, but increased the abundance in complex landscapes Fig.

However, contrary to foliar-foraging predators, predator releases had an adverse effect on parasitoid abundance in complex landscapes, but no effect in simple landscapes Fig. The effect of augmentative releases of predators on a foliar-foraging predator abundance, b ground-dwelling predator abundance, and c parasitoid abundance in landscapes of varying complexity. Predicted responses for the control solid lines and augmentative releases dashed lines treatments are calculated from the set of best supported linear and generalized mixed-effects models lme4.

A positive effect size indicates higher abundance of natural enemies in predator compared to control plots, while a negative effect size indicates lower abundance of natural enemies in predator plots. The outcome of the interaction between stinkbugs and ladybird beetles on prey predation depended on the developmental stage of the prey.

Thus, larval predation by stinkbugs was constrained by antagonistic interactions with ladybird beetles. Black bars represent predicted predation values for the combination of stinkbugs and ladybird beetles based on the multiplicative risk model However, unlike larval predation, the combination of predators neither strengthened nor weakened egg predation.

We demonstrated that the local effectiveness of predator augmentation is moderated by the composition of the surrounding landscape. Indeed, predator releases had positive trophic cascading effects that increased predation rates, reduced pest abundance and plant damage, and increased crop biomass in complex landscapes. In contrast in simple landscapes, predator releases had a negative effect on pest control, increasing plant damage and reducing crop biomass.

Thus, the interaction between local augmentative biocontrol and landscape composition not only influenced the intermediate ecosystem service of pest control, but also had downstream consequences at the crop production level. Importantly, neglecting the landscape-mediated effects on the efficacy of predator augmentation may lead to inconsistent and misleading outcomes, which ultimately has consequences for growers who wish to implement this practice. While we recognize the potential implications of our findings for the management of lepidopteran pests in the cabbage system, our discussion here focuses on identifying the ecological mechanisms underlying the variation in the effectiveness of augmentative strategies.

Knowledge of these mechanisms is key to increasing our ability to predict and understand when enemy augmentation can lead to net positive effects on pest control in a wide range of cropping systems. Previous work has illustrated the importance of naturally occurring predators and parasitoids for lepidopteran pest suppression at the field scale 43 , Here, we build on those studies by showing that the abundance of naturally occurring enemies are directly influenced by the composition of the landscape surrounding our focal fields.

Simple landscapes, defined as landscapes with high proportions of cropland, were positively correlated with the abundance of foliar and ground-dwelling predators based on the control plots.

In contrast to predators, parasitoids were far less abundant in simple landscapes. These results indicate that the relative contribution of different naturally occurring enemies to pest suppression varies across the landscape complexity gradient, as reported elsewhere 16 , On one hand, parasitoids were positively host density-dependent i.

Ground beetles, on the other hand, showed stronger positive impacts on larvae biocontrol with subsequent reductions in plant damage particularly in simple landscapes, but their densities did not respond numerically to changes in pest density. Naturally occurring coccinellids showed no clear contribution in reducing densities of pest larvae or plant damage, but they were positively associated with egg predation. Although our findings suggest that naturally occurring enemies can contribute to the regulation of P.

Therefore, complementary strategies are desirable to achieve stable and economic pest control. Results from our study suggest that augmentative releases of predators have the potential to supplement the strength of pest control provided by naturally occurring enemies under certain ecological contexts.

Over the course of our study, predation on sentinel larvae was consistently higher at sites supplemented with predators when compared with predation in control plots.

Yet, predator augmentation failed to provide consistent control of naturally occurring pest larvae across sites, which is presumably tied to differences in landscape composition.

While previous studies have identified a number of ecological mechanisms that may limit the effectiveness of augmentative biological control in the field e.

Several non-mutually exclusive mechanisms could explain the landscape-moderated effectiveness of predator augmentation on pest control reported here: 1 functional complementarity among augmented and resident enemies in complex landscapes, 2 antagonistic interactions i. First, landscape complexity can enhance the complementarity among augmented and resident enemies, and thereby the strength of pest suppression Complex landscapes containing large amounts of semi-natural habitats can provide natural enemies with alternative food sources and suitable microhabitats that together might favor the coexistence of species with overlapping feeding niches Indeed, habitat heterogeneity has been positively linked to reductions in antagonistic interactions among natural enemies, thus increasing overall pest control 33 , 35 , Our results support the idea that increasing enemy abundance may have net positive effects on pest control and plant performance, but only in complex landscapes where habitat heterogeneity may create favorable conditions for complementarity between augmented and resident enemies.

Second, our results also provide empirical support to the notion that landscape simplification potentially increase antagonistic interactions among natural enemies by reducing the diversity of habitats that provide key foraging and nesting resources enabling species coexistence.

The role of antagonism among natural enemies in the outcome of biological control can be particularly important in situations when generalist predators are released. For example, P. However, the extent to which increasing the abundance of P.

In our study, the abundance of naturally occurring coccinellids decreased significantly following the introduction of P. It is conceivable that some of the reduction in coccinellid abundance was due to the increase in dispersal from the experimental plots supplemented with P.

Regardless of the causal mechanism, increasing the abundance of P. Although P. Third, we showed that predators can disrupt one another via non-trophic interactions in a controlled laboratory experiment, which was designed to mimick a simple landscape. The effectiveness of P. Thus, our laboratory experiment results were consistent with our field findings of reduced biocontrol of P. Factors leading to reduced effectiveness of P.

Recent studies have shown that such behavioral effects are ubiquitous in biocontrol systems and potentially affect pest suppression 64 , 65 , 66 , 67 , 68 , as demonstrated herein.

In complex landscapes, some of the mechanisms of reducing niche overlap e. These results underscore the importance of considering non-trophic interactions e. Finally, the landscape context may influence the effectiveness of augmentative biocontrol via changes in the composition of the naturally occurring enemies.

Unlike our finding that augmentation effectiveness was inversely related to habitat simplification, augmentation of natural enemies has been used successfully for decades in greenhouses 69 , even though enclosed environments are arguably simpler than open-field crops.

This counterexample suggests that factors other than habitat complexity can, in some cases, determine whether positive effects of predator augmentation are realized within diverse enemy communities. Compared with open field crops, greenhouses virtually lack any naturally occurring enemies that could potentially interfere with the released agent. In fact, species richness and composition are important determinants of the range and direction of interactions among natural enemies 70 , especially in open field crops where enemy communities, even in simplified landscapes, are more complex and diverse than those of greenhouses Because there is considerable variation in the responses of different enemy taxa to changes in landscape composition, it follows that predator augmentation effects may vary in response to shifts in the identities of the species present in the local community.

Naturally occurring enemies may potentially disrupt augmented predators either directly through mutual interference or intraguild predation, or indirectly via reduction in prey densities thorough pest consumption. Therefore, the effectiveness of enemy augmentation is not determined solely by the landscape context, but by how the local enemy assemblage interacts with the augmented enemies.

Such context-dependency in the interaction among enemies hinders the formation of general rules to predict the net effects of predator augmentation across systems. Our study, nevertheless, provides new insights into the mechanisms whereby the combination of augmented and resident enemies may be expected to enhance pest control, and thereby offer a conceptual framework to make plausible predictions that are amenable to further testing in other systems. Taken together, our work clearly demonstrates that the benefits of natural enemy augmentation are landscape-dependent.

As such, our work adds to a growing set of evidence that biological pest control is not simply a function of enemy diversity and abundance, but also the landscape context in which enemies interact 72 , Fortunately, some general rules of these landscape dependency patterns have started to emerge to provide instructive management of certain landscape contexts where local agricultural practices may be more likely to enhance biological control.

For example, planting flower strips adjacent to crop fields tends to produce large effects on boosting natural enemy populations in simple landscapes, but reduced impacts in complex landscapes However, our study found landscape dependency patterns that differ from those described above, indicating that more research on augmentation practices is needed before broader conclusions can be drawn.

For example, it would be important to verify the consistency of our results over multiple cropping seasons. Also, studies in other cropping systems and geographic regions are important to test the generality of our findings. Augmentative biocontrol has long been recognized as a promising pest control alternative to conventional pesticide use when used as part of a comprehensive integrative pest managment approach. However, the effectiveness of augmentative biocontrol to manage agricultural pests in field situations has been questioned because they have mixed records of success.

Our research expands on previous work exploring the ecological factors associated with such conflicting outcomes 49 , 74 by demonstrating that the effectiveness of augmentation depends strongly on the composition of the surrounding landscape. In the context of our study region, augmentative biocontrol was more effective in suppressing lepidopteran pests in complex than in simple landscapes.

Clearly, these results are system-dependent and the specifics arising from other enemy-pest systems can create idiosyncrasies that demand case-by-case consideration. For example, a different conclusion might be reached by considering other natural enemies e. From an applied perspective, this context dependency can be frustrating, but it must be acknowledged if we hope to effectively integrate natural enemy augmentation strategies in agricultural production systems.

To this end, we need to move beyond the debate concerning the merits of using multiple vs. Ultimately, a greater understanding of landscape-moderated interactions between pests and their natural enemies would provide much needed information for pest management practitioners with respect to how and where natural enemy augmentation can be implemented more effectively. The landscape in this region is characterized by a mosaic of cropland and semi-natural habitats. Cropland in these landscapes mainly consisted of corn, soybean, winter wheat and crucifers, while semi-natural areas are composed of shrublands, woody wetlands, and mixed forest.

All farms selected for the study were either organic or used minimal inputs for pest management. These spatial scales are suitable for analyzing the effects of landscape context on pest control and natural enemies Seeds of fresh-market cabbage B. Plants were eight weeks old when they were transplanted to the field. On each of the 11 farms, we established two experimental plots. One plot was randomly chosen for the augmentative predator release treatment while the other served as a non-release control.

Care was taken to minimize fine-scale landscape heterogeneity between experimental plots within the same farm. Plots within the same farm primarily differed in the predator release treatment, while landscape context, plot size and shape, and abiotic conditions were similar for each pair. Each experimental plot consisted of ten 7.

Row and plant spacing were 0. Plants were transplanted across farms over two consecutive weeks in mid-June Experimental fields within the same farm were planted on the same day. All experimental plots were managed without fungicides or insecticides, and weeds were removed at two-week intervals. The predator release treatment included both Podisus maculiventris nymphs and Hippodamia.

Both the nymphal and adult stinkbugs display high predation rates on lepidopteran larvae, so we released fourth and fifth instars in our experiments to minimize dispersal after release and increase the potential for season-long pest control. Ladybird beetle larvae were not available commercially, which precluded us from using less-mobile stages.

Predators were released three times throughout the season at the seedling, pre-cupping, and early head formation growth stages Releases were conducted early in the season, as previous studies have shown that early control is key to the success of biocontrol strategies in field settings 80 , Approximately stinkbugs and ladybeetles were released per plot each time by carefully deploying them on the leaves.

These release rates equaled 1. These are commonly recommended release rates by commercial vendors 82 , 83 , 84 , No predators were released in the control plots. Keep in mind that all insect species are also suppressed by naturally occurring organisms and environmental factors, with no human input. This is frequently referred to as natural control.

This guide emphasizes the biological control of insects but biological control of weeds and plant diseases is also included. Natural enemies of insect pests, also known as biological control agents, include predators, parasitoids, and pathogens. Biological control of weeds includes insects and pathogens. Biological control agents of plant diseases are most often referred to as antagonists. Predators, such as lady beetles and lacewings, are mainly free-living species that consume a large number of prey during their lifetime.

Parasitoids are species whose immature stage develops on or within a single insect host, ultimately killing the host. Many species of wasps and some flies are parasitoids. Pathogens are disease-causing organisms including bacteria, fungi, and viruses.

They kill or debilitate their host and are relatively specific to certain insect groups. Each of these natural enemy groups is discussed in much greater detail in following sections. The behaviors and life cycles of natural enemies can be relatively simple or extraordinarily complex, and not all natural enemies of insects are beneficial to crop production.

For example, hyperparasitoids are parasitoids of other parasitoids. In potatoes grown in Maine, 22 parasitoids of aphids were identified, yet these were attacked by 18 additional species of hyperparasitoids. This guide concentrates on those species for which the benefits of their presence outweigh any disadvantages.

A successful natural enemy should have a high reproductive rate, good searching ability, host specificity, be adaptable to different environmental conditions, and be synchronized with its host pest. A high reproductive rate is important so that populations of the natural enemy can rapidly increase when hosts are available. The natural enemy must be effective at searching for its host and it should be searching for only one or a few host species.

Spiders, for example, feed on many different hosts including other natural enemies. It is also very important that the natural enemy occur at the same time as its host. For example, if the natural enemy is an egg parasitoid, it must be present when host eggs are available. No natural enemy has all these attributes, but those with several characteristics will be more important in helping maintain pest populations. There are three broad and somewhat overlapping types of biological control: conservation, classical biological control introduction of natural enemies to a new locale , and augmentation.

Conservation The conservation of natural enemies is probably the most important and readily available biological control practice available to growers. To be effective, natural enemies may need access to; alternate hosts, adult food resources, overwintering habitats, constant food supply, and appropriate microclimates Rabb et al. This host, another leafhopper, only overwintered on blackberry foliage in riparian areas, often quite distant from the vineyards.

Vineyards close to natural blackberry stands experienced earlier colonization by the parasitoid in the spring and better biological control. Wilson et al. Biological control is an exciting science because it constantly incorporates new knowledge and techniques.

In this section we will illustrate several ways in which time honored approaches to biological control are being adapted to meet today's pest management challenges. Because most augmentation involves mass-production and periodic colonization of natural enemies, this type of biological control has lent itself to commercial development.

There are hundreds of biological control products available commercially for dozens of pest invertebrates, vertebrates, weeds, and plant pathogens Anonymous The practice of augmentation differs from importation and conservation in that making permanent changes in a agroecosystem to improve biological control is not the primary goal. Rather, augmentation generally seeks to adapt natural enemies to fit into existing production systems. For example, cultures of the predatory mite, Metaseiulus occidentalis Nesbitt were laboratory-selected for resistance to pesticides commonly used in an integrated mite management program in California almond orchards Hoy Genetic improvement of several predators and parasitoids has been accomplished with traditional selection methods Hoy , and appears possible with recombinant DNA technology.

An excellent example of an augmentative practice than has been successfully adapted to a wide variety of agricultural systems is the inundative release of Trichogramma wasps. Trichogramma are the most widely augmented species of natural enemy, having been mass-produced and field released for almost 70 years in biological control efforts. Worldwide, over 32 million ha of agricultural crops and forests are treated annually with Trichogramma spp. In China, agricultural production and pest management systems capitalize on low labor costs, and generally follow highly innovative yet technologically simple processes.

For example, Trichogramma spp. Insectary-reared parasitized eggs are wrapped in sections of leaves which are then slipped by hand over blades of sugarcane. Most Trichogramma production in China takes place in facilities producing material for a localized area. These facilities range from open air insectaries to mechanized facilities that are leading the world in development of artificial host eggs.

One of the barriers to wider implementation of biological control in western agriculture has been socio-economics van Lenteren In current large-scale production agricultural systems, a premium is placed on efficiency and economy of scale. Entire support industries have developed around the application of agrichemicals, including application equipment manufacturing, distribution and sales, as well as application services. In order for biological control products to not be at odds with these industries, and to compete strongly with pesticides, they should have many of the same characteristics.

Ideally, they should be as effective as pesticides, have residual activity, be easy to use, and they should have the capacity to be applied quickly on a large scale with conventional application equipment. These products are annually applied to approximately 7, ha in each of Switzerland and Germany, ha in Austria, and 15, ha in France. All three products are based on manufactured plastic or paper packets designed to provide protection for the wasps against weather extremes and predation until emergence in the field.

A Trichocap opened to show eggs parasitized by Trichogramma brassicae. Upon emergence wasps exit through holes in capsule wall. Photo by D. As in the Chinese example above, European Trichogramma products are for the most part applied to crop fields by hand. One exception is the product called, Trichocaps which can be broadcast either by hand or by aircraft using conventional application equipment. Trichocaps packets are actually hollow walnut-shaped cardboard capsules 2 cm.

Developing Trichogramma inside capsules are induced into an overwintering diapause state in the insectary, then stored in refrigerated conditions for up to nine months without loss of quality.

This system allows for production of product during winter months, then distribution to growers when needed in the summer. Once removed from cold storage, Trichogramma inside the capsules will begin development and begin emergence approximately Celsius degree days later. This 'reactivation' process can be manipulated so that capsules containing Trichogramma at different developmental stages can be applied to fields at the same time, extending the emergence period of parasitoids and increasing the 'residual' activity of a single application to approximately one week.

Planning and preparation of the product for application is done by the company so that growers are only responsible for applying the product to crop fields. This strategy now has the potential for immediate commercial implementation in North America. The study of disturbance and its effects on community dynamics and the emergence of the discipline of landscape ecology are impacting the way we think about the conservation of natural enemies.

While the most highly disturbed terrestrial ecosystems may have one disturbance event every several years e. From an ecological point of view, the outcomes are predictable Odum Highly disturbed systems exhibit decreased species diversity and shortened food chains, resulting in the few well adapted species i. This requires that additional disturbance events be initiated i.

With increased reliance on mechanization and pesticides, diversity in farmlands has rapidly disappeared and the impacts on natural enemies are only now beginning to be understood Ryszkowski et al.

The goal of an ecological approach to conservation biological control is to modify the intensity and frequency of disturbance to the point where natural enemies can function effectively. This will need to occur at field, farm and larger landscape-levels. Within fields, modification of tillage intensity and frequency reduced tillage or no-tillage can leave more plant residue on the soil surface and have a positive impact on predators ground beetles and spiders. Intercropping can also modify the microclimate of crop fields making them more favorable for parasitoids.

Female Eriborus terebrans a larval endoparasitoid of the European corn borer. At the farm level, the presence and distribution of non-crop habitats can frequently be critical to natural enemy survival. Eriborus terebrans Gravenhorst is a wasp which parasitizes European corn borer larvae.

Neither of these conditions is met in a conventionally managed corn field. Therefore, wasps seek more sheltered locations in wooded fencerows and woodlots where they find reduced temperatures, higher relative humidity and abundant sources of adult food.

Current research is examining the potential of modifying corn production systems by creation of natural enemy resource habitats to provide critical resources and increase natural control of European corn borers. Intercrops, strip crops, as well as modification of grass waterways, shelterbelts, buffer and riparian zones are promising techniques.

Typical field border with flowering plants important in providing pollen, nectar, alternate hosts and refuges for natural enemies of pests in agricultural landscapes. Another factor of importance for the safety assessment is whether the control organism is a microorganism, an insect or another kind of animal. There are many similarities between microorganisms and beneficial animals in terms of potential side-effects on other organisms in the environment.

However, for microorganisms it is also very important to investigate whether they could cause disease in humans. The regulations in Europe for approval of biological control agents and products vary depending on the type of beneficial organism. Microorganisms are categorized based on the intended use, either as plant protection products or biocides, and require approval as such.

After approval of the active microorganism at EU level, the formulated product must be authorized nationally. Today, this is done in three major climate zones rather than individual countries. For insects and other small animals, there is no common European legislation and the countries address them differently. In Sweden, the Swedish Chemicals Agency is the main responsible authority for authorization of microbial agents, whereas the Swedish Environmental Protection Agency authorizes new insects and other small animals.

Stenberg slu. When is it biological control? Read more about biological control at Wikipedia. Different types of biological control There are four basic types of biological control: Natural biological control: The service carried out by resident natural enemies of pests and pathogens without human involvement. Conservation biological control: Directed stimulation of resident natural enemies to enhance their control of pests and pathogens. Augmentative biological control: Addition of propagated biocontrol agents, temporarily increasing their population densities in a targeted area.

Classical biological control: Addition of new biocontrol agents for proliferation and long-term establishment. Using biological control methods is well established in commercial greenhouse cultivation. It also works well for hobby gardens. One kind of biological control is to promote enemies to the pests that occur naturally in the environment. Ladybugs are good at eating aphids that damage the crops.