Conditions to terminate reproductive diapause of a univoltine insect: Ceratapion basicorne (Coleoptera: Apionidae), a biological control agent of yellow starthistle

Authors: Smith, Lincoln; PARK, IKJU - University Of California, Davis

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/11/2021
Publication Date: 10/8/2021
Citation: Smith, L., Park, I. 2021. Conditions to terminate reproductive diapause of a univoltine insect: Ceratapion basicorne (Coleoptera: Apionidae), a biological control agent of yellow starthistle. Environmental Entomology. 51(1):71-76. https://doi.org/10.1093/ee/nvab110.
DOI: https://doi.org/10.1093/ee/nvab110

Interpretive Summary: Biological control using host-specific insects can be an extremely cost-effective and environmentally benign method to manage invasive alien weeds. However, it can take years to increase populations of the insect to the level where they effectively control the target weed. This is especially true of insects that have only one generation a year. The rosette weevil (Ceratapion basicorne) is a recently approved biological control agent of yellow starthistle (Centaurea solstitialis), which has invaded about 20 million acres of rangeland in the western US. We studied the environmental conditions required to terminate winter hibernation of this insect in the laboratory to determine the minimum time required. Our results indicate that 8 weeks in a refrigerator enabled 80% of females to begin laying eggs, which rose to 95% after 11 weeks. This knowledge may enable us to artificially produce two generations per year which would greatly increase the number produced for release in the field to control yellow starthistle. This method may be suitable for other insect biological control agents that have only one generation per year.

Technical Abstract: Ceratapion basicorne is a recently approved univoltine biological control agent that develops inside the rosette of yellow starthistle (Centaurea solstitialis), an invasive annual plant. Adult weevils normally emerge in early summer, and females are thought to be in reproductive diapause until the following spring, when they oviposit in rosettes. The long period of reproductive diapause constrains mass-rearing this weevil because only one generation per year can be produced. Determining the environmental conditions that regulate diapause termination may enable shortening diapause under laboratory conditions to increase production of adults to release. We tested three hibernating conditions (greenhouse [ambient temperature and photoperiod], glass door refrigerator [5°C and ambient photoperiod], and growth chamber [5°C and 24 h dark]) for three durations (4, 8, 11 weeks). The highest proportion of females laying eggs came from the growth chamber, with 40% terminating diapause after 4 weeks, 80% after 8 weeks, and 95% after 11 weeks of exposure. Our study demonstrates that duration of cold temperature is an important stimulus to terminate reproductive diapause of C. basicorne, and that exposure to ambient light had no effect at 5°C. However, we predicted that 90% of females held at ambient greenhouse conditions, without any chilling period, would terminate diapause after 23 weeks, suggesting that this weevil is adapted to a wide range of winter conditions. Reducing the winter diapause period from about 6 months to 11 weeks should enable the production of multiple generations per year to increase the number of insects available to release.