Pennies for Parasitoids: Savings Add Up When Rearing Wasps on Alternate Hosts
By Edward Ricciuti
Getting more bang for the buck out of mass production is the Holy Grail for manufacturers, whether they are making automobiles, appliances, or natural enemies that can be used as biological control agents against pest insects. Sometimes, as research in Brazil suggests, the most cost-effective method requires a little tweaking of what actually happens in the field.
As reported today in the Journal of Economic Entomology, experiments have shown that the parasitic wasp Telenomus remus can be cheaper to raise on a commercial scale on the eggs of an alternate host, rather than those of the fall armyworm (Spodoptera frugiperda), the pest the wasp naturally parasitizes in the field. How much cheaper? Half the cost, which translates to $0.0002 per parasitoid compared to $0.0004—a difference that adds up when T. remus wasps are reared by the millions.
Instead of using the eggs of its natural host to rear the parasitoid, the scientists substituted those of the rice moth (Corycyra cephalonica). “Rearing of the parasitoid T. remus in C. cephalonica eggs is cheaper for several reasons,” says Alessandra Marieli Vacari, Ph.D., at the University of Franca, Sao Paulo, Brazil, and a coauthor of the study. The diet fed to growing rice moths, 97 percent wheat germ and 3 percent brewer’s yeast, costs less than the five-star mix needed by the armyworm, which includes not only wheat germ but also antibiotics, beans, agar, casein, anti-contaminants, ascorbic acid, and water. Armyworm larvae cannibalize one another so must be grown one to a vial, an expensive proposition for mass production, given the number of vials required and the increased time and effort to maintain each individual larva.
T. remus is a scourge of fall armyworm eggs, parasitizing them at rates up to 90 percent, even more in some cases, a plus for farmers in places such as Brazil, where it is the paramount maize pest. Its use in Brazil is limited by the cost required to raise sufficient numbers of adult wasps.Pest managers have sought a less expensive method of producing the parasitoid, perhaps even allowing its production via a cottage industry.
The rice moth is ideal as a production host for T. remus because it is easily reared and maintained in the laboratory. Another plus is it has a shorter life cycle yet produces more eggs than the fall armyworm, so more parasitoids can be grown per batch of eggs.
Several factors were used by the researchers to estimate the operational cost of production, including the number of parasitized eggs, percentage of emergence, longevity, survival, sex ratio, egg-to-adult period, and density per unit of rearing of T. remus in S. frugiperda and C.cephalonica eggs. To ensure early estimates of cost efficiency were not a fluke, the scientists used biological data for T. remus reared in C. cephalonica only after the adaptation of the parasitoid to the host in the sixth generation.
Achieving a high level of cost efficiency requires finding a balance between the use of resources, rate of production, and quality of the goods being produced. The researchers took into account costs that would be considered by any manufacturer hoping to realize the most profit out of production, including the expenses incurred for conducting the activity and depreciation of items such as equipment and furniture. Other factors weighed included labor and energy to operate equipment.
“This study opens up the possibility of using the alternative host C. cephalonica eggs in the rearing of T. remus parasitoids, producing a natural enemy that has an adequate market price and that will allow profitability and profit for the producing biofactories,” say the researchers.
Journal of Economic Entomology
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.