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Title: CONTROLLED FIELD INFESTATIONS WITH WESTERN CORN ROOTWORM (COLEOPTERA: CHRYSOMELIDAE) EGGS IN MISSOURI: EFFECTS OF EGG STRAINS, INFESTATION DATES,AND INFESTATION LEVELS ON CORN ROOT DAMAGE

Author
item Hibbard, Bruce
item Barry, B
item Darrah, Larry
item Jackson, Jan
item Chandler, Laurence - Larry
item FRENCH, L - FRENCH AGRI RESEARCH INC
item MIHM, J - FRENCH AGRI RESEARCH INC

Submitted to: Journal of Kansas Entomological Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/22/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: Natural infestations of corn rootworms lack uniformity and an accurate density estimate is extremely difficult to obtain. Artificial infestations of corn rootworm eggs overcome these problems, but require laboratory rearing of the insect. A number of insect species have been documented to perform less vigorously in the field after laboratory rearing when compared to wild populations of the same species. Damage due to infestations from a wild strain of the western corn rootworm was evaluated along with damage due to infestations from 2 strains that had been maintained in the laboratory for 11 and 100 generations respectively. Damage caused by the strain reared 11 generations was not significantly different than the damage caused by the wild strain in any trial. The strain reared for 100 generations caused significantly more damage than the other two strains in 1995 and in 1 location in 1996, probably due to a more synchronous hatch. The wild strain caused significantly more damage than the strain reared 100 generations at the second location in 1996, possibly due to low soil temperatures reducing hatch in a strain that had not been exposed to cold temperatures. As a result of this research, we can be assured that laboratory rearing on corn for 11 generations does not significantly affect the ability of corn rootworm larvae to cause damage and we will continue to use laboratory-reared corn rootworm eggs in our field studies.

Technical Abstract: Damage due to infestations from a wild strain of the western corn rootworm, Diabrotica virgifera virgifera LeConte, was evaluated along with damage due to infestations from 2 strains that had been maintained in the laboratory; a diapausing strain reared for ~11 generations and a nondiapausing strain reared for more than 100 generations. Eggs were infested at 2 infestation levels (600 and 1,200 eggs/30.5 cm) and 2 infestations times (2-leaf stage and 5-leaf stage) in 1 location in 1995 and 2 locations in 1996 (a planting-time infestation was also tested at the second location in 1996). Damage caused by the diapausing strain was not significantly different than the damage caused by the wild strain in 1995 or in either location in 1996. The nondiapausing strain caused significantly more damage than the other two strains in 1995 and in 1 location in 1996. The wild strain caused significantly more damage than the nondiapausing strain at the second location in 1996, possibly due to soil temperatures that were cool for an extended period of time. Infestations at the 2-leaf stage caused significantly more damage than infestations at the 5-leaf stage and infestations of 1,200 eggs/30.5 cm caused significantly more damage than infestations of 600 eggs/30.5 cm. The lone planting-time infestation caused significantly more damage than the 2-leaf or 5-leaf stage infestations, but the phenology of infestation differed from that typically found with natural infestations (pupation peaked with knee-high corn).