Pests Stay In, Parasitoids Fly Out: The Augmentorium for Biological Control in IPM
As an old Disney song proclaims, “Everything Has a Useness,” and it appears that goes even for squishy fruit infested with fruit flies. Yucky as it might seem, rotting fruit laden with fruit fly larvae is the nucleus of a device that promises to enhance the biological control element of integrated pest management (IPM) in vegetable fields and orchards.
It’s called an “augmentorium,” and, simply put, it is a tent that covers fruit infested with the larvae of flies or other pest insects—and, importantly, the wasps that parasitize those pest larvae. The tent is equipped with a mesh, of which the gauge (i.e., the size of its holes) is large enough to allow adult parasitoid wasps to escape and continue to act as biological control agents but small enough to keep the pest fruit flies penned in. This enables field sanitation (i.e., removing infested fruit), an important component of many IPM programs, without loss of helpful parasitoid wasps.
The technique that employs the device, developed about 15 years ago in Hawaii, is called augmentative biological control, which works by raising and releasing large numbers of natural enemies to augment their numbers already existing in nature, in hopes of overwhelming pest populations. A potential application of this process, for management of olive fruit flies (Bactrocera oleae) and Mediterranean fruit flies (Ceratitis capitata), is described in a paper published in late May in the open-access Journal of Insect Science.
The name “augmentorium” comes from its use in augmentative biological control (and, by extension, from the Latin augere, meaning “to grow”). Included in IPM, augmentorium use in a fruit or vegetable production system will likely increase the toll taken by parasitoids on the target pest, lowering its numbers and thus increasing crop yield.“On its own, the augmentorium is not a magic bullet,” says Gaylord A. Desurmont, Ph.D., lead author on the study, “but we believe it can have an important impact as part of an integrated pest management program and even improve specific IPM implementations from the perspective of minimizing insecticide applications.” Desurmont works for the U.S. Department of Agriculture’s Agricultural Research Service, in its European Biological Control Laboratory in France, where the research was conducted. It is one of four such laboratories in countries that are the native homes of many plants and insects that are invasive in the United States, as are the flies in the study.
Effective, nontoxic, and relatively cheap, augmentation of the impact of natural enemies via this technique has not been extensively used commercially, especially in the United States. Although simple to use, augmentorium systems are highly species specific, both to pests and parasitoids, particularly when it comes to the size and shape of screen mesh. Mesh size must be precisely tailored to the size of both the target pest and its parasitoids, to keep the former in and allowing the latter out. Color and material of the mesh must also promote escape of the parasitoids and hold up during extended field use.
In the new study, of the five screen types tested, one was deemed best for designing an augmentorium deployable for commercial use. It retained 90 percent of the adult olive fruit flies and all of the Mediterranean fruit flies (Medflies) that emerged while permitting the escape of 72 percent of adult Psyttalia lounsburyi parasitoid wasps and 94 percent of P. ponerophaga wasps. It has a clear polyethylene high-density mesh at a size of 3-by-2 millimeters and lasts in the field for four to five years.
The research has had another benefit, namely development of a simple way to test multiple screens for effectiveness. Field testing can be expensive and time consuming, say they authors. Instead, they opted for laboratory testing using mini-augmentoria enclosed in a larger plastic container that retained the emerging adult wasps for counting.
Both wasp species in the study attack larvae of the flies while they are developing in fruit tissue, laying their eggs in the fly larvae. Wasp larvae then develop inside the fly larvae and emerge as adults from fly pupae. In their native range, these parasitoids can have a strong impact on wild populations of their hosts. Psyttalia lounsburyi, successfully introduced in the United States against the olive fruit fly, shares a sub-Saharan African origin with the olive fruit fly and the Medfly, while P. ponerophaga originates in Pakistan.
The augmentorium strategy already has proven workable as a biocontrol tool against another fruit pest, the spotted-wing drosophila (Drosophila suzukii), and has been used in La Réunion Island against tephritids, another family of fruit flies. The goal of biocontrol is not to completely eliminate a pest but to ensure a balance with its natural enemies to keep damage economically acceptable. It fails if coupled with heavy application of broad-spectrum insecticides, which kill not only pests but also their natural enemies, and so it is best coupled with other non-chemical management practices.
In the course of field sanitation, instead of destroying infested fruit or vegetables, growers can place them in an augmentorium, ensuring that no more pests will emerge from these fruits but that the parasitoids that may be inside the pests will safely emerge. Adding an augmentorium to contain pests can be an important way to improve the impact of natural enemies, which can be used in combination with other environmentally friendly practices. The authors plan to move next to field tests to test this proposition in olive systems.
“Identifying an Optimal Screen Mesh to Enable Augmentorium-Based Enhanced Biological Control of the Olive Fruit Fly Bactrocera oleae (Diptera: Tephritidae) and the Mediterranean Fruit Fly Ceratitis capitata (Diptera: Tephritidae)”
Journal of Insect Science
Ed Ricciuti is a journalist, author, and naturalist who has been writing for more than a half century. His latest book is called Bears in the Backyard: Big Animals, Sprawling Suburbs, and the New Urban Jungle (Countryman Press, June 2014). His assignments have taken him around the world. He specializes in nature, science, conservation issues, and law enforcement. A former curator at the New York Zoological Society, and now at the Wildlife Conservation Society, he may be the only man ever bitten by a coatimundi on Manhattan’s 57th Street.