The cooler than normal spring temperatures will most likely delay normal emergence of leafy spurge flea beetles, which is a bio-control agent because their life cycle is based on growing degree days much like plants, explained Darrell Deneke, SDSU Extension IPM program coordinator.
"However, as our day time temperatures rise, the likelihood of adult flea beetle emergence also increases, so now is a good time to start watching for adult flea beetles," Deneke said.
South Dakota has been using the leafy spurge flea beetle as a bio-control agent to manage the noxious weed, leafy spurge since the 1980s.
In the early years, Deneke said several species of the leafy spurge flea beetle were studied and released, but today two species are most commonly used. They include the black flea beetle, Aphthona lacertosa and the brown flea beetle, Aphthona nigriscutis.
"These two species of leafy spurge flea beetles have been very effective in the battle of managing leafy spurge infestation across the state," Deneke said. "This group of flea beetles is very host specific to the leafy spurge plant, which is why they make an ideal bio-control choice."
The flea beetles typically take three to five years to establish and impact leafy spurge infestations. The adult will do some plant feeding, but it is the larval form of the insect that causes the lethal injury to the leafy spurge plant. The newly hatched larvae will feed on the leafy spurge roots and root hairs ultimately affecting the plants ability to utilize water and nutrients. Deneke explained that this weakens the plant and makes it vulnerable to disease and winter survival.
The state of South Dakota has a program promoting the collection and distribution of leafy spurge flea beetles.
"Each year the South Dakota Department of Agriculture organizes leafy spurge collections around the state where land owners can help collect the flea beetles to be released on their leafy spurge infestations," Deneke said.