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ARS Home » Southeast Area » Tifton, Georgia » Crop Protection and Management Research » Research » Publications at this Location » Publication #166159
Title: THE CO-OCCURRENCE OF AN INTRODUCED BIOLOGICAL CONTROL AGENT (COLEOPTERA: COCCINELLA SEPTEMPUNCTATA) AND AN ENDANGERED BUTTERFLY (LEPIDOPTERA: LYCAEIDES MELISSA SAMUELIS)

Author
item SHELLHORN, N - R&D INSTITUTE/AUSTRALIA
item LANE, C - ECOL. STRATEGY CONSULTANT
item Olson, Dawn

Submitted to: Journal of Insect Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/15/2004
Publication Date: 1/15/2005
Citation: Shellhorn, N. A., Lane, C., Olson, D. M. 2005. The co-occurrence of an introduced biological control agent (Coleoptera: Coccinella septempunctata) and an endangered butterfly (Lepidoptera: Lycaeides melissa samuelis). Journal of Insect Conservation. 9(1):41-47.

Interpretive Summary: Whether a biological control agent presents a non-target risk to a native species depends if they co-occur spatially and temporally, and if the agent will harm the native species. We sampled two study sites during 1993 in Minnesota and Wisconsin to survey predators and parasitoids of the extant populations of the federally endangered Karner blue butterfly, Lycaeides melissa samuelis. We also determined the growth and survival of neonate larvae of the butterfly at the Wisconsin site only. We found the introduced coccinellid Coccinella septempuntata co-occurring spatially and temporally with eggs, larvae and adults of L. m. samuelis. The two species were also observed together on the latter's sole host plant, Lupinus perennis, and in Wisconsin, an adult C. septempunctata was observed consuming second instar larvae of L. m. samuelis. Using a simple model to hypothesize the risk that C. septempunctata presents to L. m. samuelis, we showed that increases in predator density could greatly increase mortality to L. m. samuelis. At these sites, C. septempunctata were reproducing and had access to summer aphids and suitable overwintering habitat. Nearby agricultural crops could provide spring aphids for oogenesis, and assist with C. septempunctata population build-up. Maintaining a minimum isolation distance between agricultural crops known to harbor aphids and extant Karner blue butterfly populations may need to be considered as part of the butterfly management program.

Technical Abstract: Coccinella septempunctata L. is an introduced biological control agent against general species of aphids in agricultural crops. However, this species has been recovered from fragment habitats containing the federally endangered butterfly species L. m. samuelis and may reduce the butterfly population because of its general feeding prefernces. We studied both species populations and other natural enemies of the butterfly species at two locations; in western Minnesota, and east central Wisconsin. Both study areas support extant populations of L. m. samuelis and have a Plainfield sand soil type that supports an oak savanna, barrens- type community. This community is characterized by 10-70% cover of Quercus velutina Lam. or Pinus banksiana Lamb., with an understory containing prairie and savanna forbs including L. perennis. The most notable difference between the two sites was geological. Minnesota sites are located in the Paleozoic plateau, believed to have escaped glacial overriding during the Wisconsin glaciation, and consequently the topography is very dissected, with steep slopes up to 45 degrees. The Wisconsin sites were glaciated during the Pleistocene epoch and the topography is flat to rolling hills. At the study sites, we surveyed predators and parasitoids in different microhabitats created by tree canopy cover and topographic slopes. In a 0.5-1 ha areas with microhabitat ranging from open-to-closed tree canopy cover and slope ranging from moderate-to-steep, we sampled 30 randomly selected 0.25 m2 grids. We randomly sampled plants depending on the density of lupine within the grid with a minimum of 2 and a maximum of 4 plants. We recorded the number and type of predators, parasitoids and herbivores. We also determined larval performance in microhabitats with different tree cover and topographic slopes, by placing neonate Karner blue larvae on randomly selected lupine plants in the microhabitats and monitoring every 2-3 days for growth and survival, presence of natural enemies and ant tending. We also developed a simple model to generate a hypothesis about the risk that C. septempunctata presents to L. melissa samuelis. We utilized various published records and observations from our survey to determine the rate of increase of the 1st brood butterfly population which represented all factors affecting the butterfly during the 1st brood excluding effects of predation and overwinteirng mortality, the density of C. septempunctata adults and L. melissa eggs per plant, and the mid-attack rates on aphids by3rd instar C-7 larvae on beans (Vicia faba) and peas (Pisum sativum). The density of lupine was obtained from counting plants within our grids after sampling for predators and parasitoids. The model predicts that if the density of the beetle increased from 0.0.074 to 1.0 beetle per plant the beetle could eat 57% of the butterfly eggs and larvae if all encounters resulted in mortality. These results suggest a potentially large effect on the butterfly population especially is agricultural fields with aphid populations are close by.