Author
 |
CHARLET, LAURENCE |
|
Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 4/26/2002 Publication Date: 10/1/2002 Citation: CHARLET, L.D. PARASITIZATION OF THE RED SUNFLOWER SEED WEEVIL (COLEOPTERA: CURCULIONIDAE) BY ITS LARVAL PARASITOID, TRIASPIS AEQUORIS (HYMENOPTERA: BRACONIDAE) IN CULTIVATED SUNFLOWER. ENVIRONMENTAL ENTOMOLOGY. 2002. V. 31 (5). P. 844-851. Interpretive Summary: The red sunflower seed weevil is a pest of sunflower in the northern and central Plains sunflower regions. Weevil larvae feed and develop in the sunflower seeds and overwinter in the soil. Studies were conducted to determine the parasite species attacking the seed weevil, the seasonal abundance of the parasites, emergence pattern of the weevil and parasites, distribution of weevils and parasitism within the sunflower head, and the impact of planting date as a control strategy. A total of 630 parasites emerged from seed weevil larvae recovered from North and South Dakota and Minnesota from 1991 to 1995 and were identified as Triaspis aequoris. Parasitism ranged from 2.5 to 24.2% per year. There was an increase in the percentage parasitism as overall weevil populations decreased over years. Activity by T. aequoris may have contributed to the decline of the red sunflower seed weevil from the northern Plains. In Nebraska, between 1993 and 1995, percent parasitism by T. aequoris, the only species recovered, increased with increasing weevil densities. Patterns of emergence for both red sunflower seed weevil and T. aequoris were similar in two locations in North Dakota. Weevil oviposition pattern in seeds of the sunflower head showed decreasing density toward the center, but T. aequoris parasitism was equal throughout. Triaspis aequoris effectively searched for and attacked weevil eggs as soon as females began laying eggs in the field. Date of planting studies showed that damage from weevils increased as seeding of fields was delayed, but parasitism was similar among all dates. The parasite appears to be an efficient natural enemy of the red sunflower seed weevil, well adapted to the biology of its host, and amenable for use with some pest management strategies in cultivated sunflower. Technical Abstract: The red sunflower seed weevil is a pest of sunflower in northern and central Plains. Weevil larvae feed and develop in the sunflower achene dropping to the soil to overwinter. A total of 630 parasitoids emerging from weevil larvae recovered from North (ND) and South Dakota (SD) and Minnesota (MN) from 1991 to 1995 were identified as Triaspis aequoris Martin (Hymenoptera: Braconidae) a solitary koinobiont endoparasitoid. The mean parasitization rate for red sunflower seed weevil by T. aequoris ranged from 2.5 to 24.2% per year. There was an increase in the percentage parasitization as overall weevil populations decreased over years. In Nebraska, percent parasitization by T. aequoris, the only species recov- ered, increased with increasing densities of S. fulvus between 1993 and 1995. Patterns of emergence for both red sunflower seed weevil and T. aequoris were similar in two locations in ND. Oviposition pattern in seeds in the sunflower head showed decreasing density toward the center, but T. aequoris parasitization was equal throughout the head. Triaspis aequoris is an egg-larval parasitoid and effectively searched for and attacked weevil eggs as soon as weevil oviposition had begun in the field. Date of planting studies showed that damage from weevils increased as seeding of fields was delayed, but parasitization of weevil larvae was similar among all dates. Activity by T. aequoris may have contributed to the decline of red sunflower seed weevil from ND and SD and MN. Lower densities of weevils also may account for reduction in parasitoid species richness of this weevil. The parasitoid appears to be adapted to its host, an effi- cient parasitoid of the weevil and amenable for use with some pest management strategies in cultivated sunflower. |
