Larval development of the knapweed biological control agent Larinus minutus (Coleoptera: Curculionidae)

Larinus minutus, a biological control agent of invasive knapweeds has become established in several states and provinces since initial North American introduction.  To better describe the larval development, sexually mature weevils were field collected from a spotted knapweed plot at the University of Arkansas Agriculture Experiment Station.  Weevils were allowed to mate for two days after which females were placed individually in a corresponding mesh bag attached to a capitulum and allowed approximately 24 hours to oviposit.  Three days from oviposition, randomly collected caged capitula were dissected biweekly and larval instar determined with head capsule measurements.  When a majority of larva reached pupation, alternate day observations were conducted on remaining caged capitula to determine average emergence date.  Two cohorts occurring at peak and late flower were used in order to observe season related development differences.  Average development times for each instar could not be determined as each instar was not fully represented.  Compared to previous publications, accelerated egg to pupation times were reported with the peak flower cohort (x̅±SE) occurring in 21.25±1.11 days and late flower 16.79±0.50 days.  Finally, adult emergence from oviposition occurred at 26.88±0.75 days in the peak flower cohort and 25.64±0.41 days in the late flower cohort.