PMN Crop News Homepage   

Posted 21 May 2007. PMN Crop News.

Artificial Diet Used to Rear Adult Insects From Larvae

University of California-Davis.

Davis, California (May 8, 2007)--A new method to use an artificial diet to rear adult insects from larvae could help scientists discover biological control agents for yellow starthistle and other alien weeds more quickly.


Classical biological control is an environmentally safe, economical method to achieve long-term management of invasive alien weeds. It involves the discovery of insects or pathogens that attack only the target weed.

“The discovery of new insect biological control agents depends on knowing the plants on which they develop,” says U.S. Department of Agriculture scientist Lincoln Smith (Agricultural Research Service). “During foreign exploration for new agents, it’s best to look for immature insects that develop on the target weed, however, it’s only possible to identify adult insects. Larvae that develop inside plant stems and roots are especially interesting for biological control, but they have been the most difficult to rear to adulthood.”

Scientists developed an artificial diet that was previously developed to mass rear purple loosestrife root weevils and has been adapted to produce adults from insect larvae found feeding inside other plant species that are targeted for biological control.

A diet transfer kit was developed to allow scientists to easily rear internal-feeding larvae that they discover during foreign expeditions. The adults can then be identified and used to start laboratory colonies that are necessary to further evaluate the safety and potential efficacy of the insects.

“The diet transfer kit contains vials of diet that can be easily transported and used in the field,” says Smith’s research partner, USDA entomologist Nada Tomic Carruthers (Animal and Plant Health Inspection Service-Plant Protection and Quarantine). “Larvae dissected from plants are placed in the diet and held until larvae complete development. With this new tool, scientists can obtain taxonomic identifications of insects that otherwise would be impossible to identify as larvae and provide live specimens for further research on host plants.”

Smith's European colleagues used the diet to rear root crown weevil larvae that they dissected from yellow starthistle plants in Turkey. They were also able to rear fly larvae dissected from perennial pepperweed roots. A colleague in Montana reared field-collected larvae of the spotted knapweed root-boring weevil.

“The fact that this diet works for flies as well as weevils, and that it works for insects from at least three species of plants and two plant families, suggests that this method can have widespread use to accelerate the discovery of new internal-feeding biological control agents,” says Smith.

Foreign exploration for new biological control agents is very difficult because scientists must go to areas where they can find the weed in its natural range. A weed that is abundant and widespread in the U.S. is often rare and localized in its native range, because it is under natural control. Prospective biological control agents are usually even more rare and localized. So, when scientists discover an insect in the field in the weed’s natural range, it is very important to be able to identify it and to obtain specimens for preliminary experimental evaluation.

“This rearing kit provides a simple, low-tech way for scientists to take advantage of the new insects they discover,” says Smith.

Smith and colleagues will evaluate modifications of the diet to improve survivorship of the insects and test it on additional species of insects and plants.

The University of California Exotic/Invasive Pests and Diseases Research Program funded this research. For more information about yellow starthistle and other weeds, visit

The UC Exotic/Invasive Pests and Diseases Research Program targets research on exotic pests and diseases in California. The program aims not only to improve our knowledge and management of pests that are already here, but also to reduce the potential impact of those pests and diseases that pose a threat to the state. The program is a collaboration between the UC Statewide Integrated Pest Management Program and the UC Riverside Center for Invasive Species Research. U.S. Department of Agriculture, Cooperative State Research Education and Extension Service, funds the program.

Stephanie Klunk