The MyAgLife podcast recently conducted an interview with Suterra’s Senior Manager of Technical Field Services, Dr. Emily Symmes. In the interview, Symmes discusses why natural enemies are important, and how to get the most out of them in your orchards.
You can listen to Symmes’ interview on the MyAgLife website here. Below are some of the key points emphasized with regard to beneficial organisms and pest management.
Six-spotted thrips. Photo credit UC IPM
“When we kill off the natural enemies of a pest, we inherit their work.” Symmes asserts that this quote by University of California entomologist Dr. Carl Huffaker, taken from a 1976 New York Times article about pest management, encapsulates the value of beneficial species in agriculture. If provided an environment to thrive, natural enemies can aid in controlling a plethora of agricultural pests - often at no added cost to the grower.
Natural enemies are often classified as generalists or specialists when it comes to how they interact with their hosts or prey. Generalist predators, including green lacewings, ladybirds, and mantids, will feed on a wide variety of other organisms, including pest insects and mites. These species may be helpful and are often widely recognized among crop producers and gardeners alike. However, specialist natural enemies are often the real ‘firepower’ when it comes to biological control.
Specialist natural enemies preferentially (and sometimes exclusively) target a certain species. Understandably, it can be immensely helpful to have insects on your farm that selectively seek out and target harmful pests. While there are some predators that are more specialized, many specialist species are parasitoids, typically wasps or flies. Parasitoids lay their eggs in or on the body of their preferred host species. As the eggs hatch and the parasitoid larvae develop, they eventually kill their host before emerging as adults to start the cycle all over again.
In practice, growers largely have two options for incorporating and taking advantage of biological control in their crops: augmentation and conservation. With augmentation biological control, the natural enemies are purchased from commercial insectaries and released into the crop.
Conservation biological control involves identifying which natural enemies are already present in the cropping system and avoiding practices that are detrimental to their survival. For example, six-spotted thrips, a naturally-occurring species, has become the predominant predator of spider mites in California orchards. Growers are increasingly limiting insecticide materials that negatively impact these thrips, leading to better biological control of spider mites.
Not all beneficial natural enemies for pest management are other insect or mite species. In a practice known as enhancement biological control, many growers have found that providing habitat for insectivorous birds and placing bat houses in or near their orchards has aided in reducing pest populations of Lepidopteran pests, such as codling moth and navel orangeworm.
Navel orangeworm larvae infected with parasitoid wasp larvae. Photo credit Emily Symmes
Natural enemies can provide an incredible service to growers who take measures that allow them to survive and thrive in their crops. However, natural enemy insects and mites are often equally, if not more, vulnerable to pesticides than the pests they target. If predators and parasitoids are disrupted by overuse of insecticides or miticides, the crop’s natural system of biological control can collapse.
To keep this system in place, many growers are reducing their pesticide use by relying on integrated pest management strategies to consistently keep pest populations low. A keystone of many IPM programs is mating disruption, which renders male pests unable to find females to reproduce with. Mating disruption and biological control are highly complementary approaches in an IPM program. Mating disruption drives pest populations to very low levels where biological control can have its greatest impact. Without the toxic effects of pesticides, and because mating disruption is species-specific to the target pest, natural enemies are allowed to flourish.
Another strategy Symmes mentions to bolster beneficial populations may seem counterintuitive at first. Specialist biological control agent populations will not persist without resources (food for predators, developmental hosts for parasitoids). Therefore, it is necessary to tolerate low populations of their target pest in the environment in order for the beneficials to persist and provide their services.
To create an IPM strategy that will best fit the ecosystem of your crop, you will first need to identify which beneficial species are active in the environment. Symmes stresses that consistent monitoring is the best way to learn about your crop’s unique food web.
Monitoring for natural enemies can take several different forms depending on the pest, natural enemy, and crop you are dealing with. For predators, scouting or trapping will involve looking directly for the insect or mite itself. In the case of parasitoids, you will often be scouting for evidence of their presence, rather than finding the insect itself. For example, most parasitoid wasps will leave exit holes and cause discoloration of their hosts. Symmes references the UC IPM website as a helpful tool for learning about the best monitoring approach for each pest in each crop.
If you have any questions about monitoring, mating disruption, or integrated pest management, Suterra’s experts are happy to help. Contact your local representative or email us online using this form.