Biology and field observations of Penthobruchus germaini (Coleoptera: Bruchidae), a biological control agent for Parkinsonia aculeata (Caesalpiniaceae)

The life cycle of the bruchid beetle Penthobruchus germaini (Pic) was studied in the laboratory and some field observations were recorded. Most adults (90.5%) emerged from the seeds of Parkinsonia aculeata L. by making an exit hole at the end of the seed opposite the radicle. Adult longevity with different food types ranged from 11.2 to 59 days and oviposition from 22 to 348 eggs per female. Females laid an average of 2 eggs per day during their life span. The life cycle (oviposition to adult emergence) was completed in 38.7 days at 30 °C in the laboratory, including 8.6 days for the egg stage, 21.8 for the larval stage, and 8.3 for the pupal stage. The larval stage had four instars. Larvae destroyed the seeds by consuming 90–100% of the cotyledons, preventing germination. They pupated inside the seeds, and only one adult emerged per seed. At three field sites, 48% of the pods were found to have eggs; the mean number of eggs per seed was 0.37 and per pod was 0.98. Females preferred the swelling of the pod as oviposition site. Mature (purple) and larger pods contained more eggs than immature (green) and smaller pods. Larvae overwintered in the seeds on the ground, began pupating in late winter, and adults emerged in the spring. Depending on plant phenology, two generations per year are possible. Natural parasitism of P. germaini was <5%. P. germaini has several attributes as an effective natural enemy of P. aculeata.