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ARS Home » Pacific West Area » Albany, California » Western Regional Research Center » Invasive Species and Pollinator Health » Research » Publications at this Location » Publication #383526

Research Project: Management of Invasive Weeds in Rangeland, Forest and Riparian Ecosystems in the Far Western U.S. Using Biological Control

Location: Invasive Species and Pollinator Health

Title: Topical application of synthetic hormones terminated reproductive diapause of a univoltine weed biological control agent

item PARK, IKJU - University Of California, Davis
item Smith, Lincoln

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/3/2021
Publication Date: 9/16/2021
Citation: Park, I., Smith, L. 2021. Topical application of synthetic hormones terminated reproductive diapause of a univoltine weed biological control agent. Insects. 12(9). Article 834.

Interpretive Summary: Yellow starthistle (Centaurea solstitialis) is an invasive annual plant that has infested multi-million acres in the western United States, causing multi-billion dollars of losses and management costs. The rosette weevil (Ceratapion basicorne) recently has been approved for biological control of this weed. However, this weevil reproduces only once a year, which hinders mass-rearing them for release. Here, we tested whether insect hormones can break the reproductive diapause (winter dormancy) of female weevils. We found that applying two insect hormones, 20E and methoprene, can consistently terminate diapause of female weevils to enable them to lay eggs. Thus, topically applying insect hormones could be used to induce females to lay eggs at any time of year, which would permit rearing more than one generation per year. This could greatly increase the number of weevils produced per year in a mass rearing program to accelerate the release of rosette weevils to help suppress yellow starthistle in the United States.

Technical Abstract: Classical biological control is an important method for controlling invasive alien weeds. Univoltine insects can be highly effective biological control agents of annual weeds because they are well synchronized with their host plant. However, having only one generation per year makes it difficult and slow to multiply them in the laboratory for initial field releases. If it were possible to terminate reproductive diapause early, then we could rear multiple generations per year, which would greatly increase annual production. We used a recently approved biocontrol agent, Ceratapion basicorne (a univoltine weevil), for yellow starthistle (Centaurea solstitialis) as a model system to study the use of two insect hormones, 20-hydroxyecdysone (20E) and methoprene, to terminate reproductive diapause. Methoprene (1 µg applied topically) terminated reproductive diapause of female weevils, whereas doses of 0.0, 0.01 and 0.1 µg did not. The combination of methoprene and 20E had a stronger effect and induced increase in adult feeding and eggs compared with a control group. Thus, topical application of these hormones should enable us to rear the weevil out of its normal season and produce more than one generation per year, which will increase productivity of mass-rearing it for field release.