Milkweed: A resource for increasing stink bug parasitism and aiding insect pollinator and monarch butterfly conservation

Authors: Tillman, Patricia - Glynn; Carpenter, James

Submitted to: International Symposium on Biological Control of Arthropods
Publication Type: Proceedings
Publication Acceptance Date: 3/4/2013
Publication Date: 3/4/2013
Citation: Tillman, P.G., Carpenter, J.E. 2013. Milkweed: A resource for increasing stink bug parasitism and aiding insect pollinator and monarch butterfly conservation. International Symposium on Biological Control of Arthropods. pp.

Interpretive Summary: The flowers of milkweed species can produce a rich supply of nectar, and therefore, planting an insecticide-free milkweed habitat in agricultural farmscapes could possibly conserve monarch butterflies, bees and other insect pollinators, as well as enhance parasitism of insect pests. In peanut-cotton farmscapes in Georgia, stink bugs, i.e., Nezara viridula, Euschistus servus, and Chinavia hilaris, develop in peanut and then disperse at the crop-to-crop interface to feed on fruit in cotton. Strategic placement, in time and space, of a milkweed habitat at these crop-to-crop interfaces may lead to successfully increasing biocontrol of stink bugs in these agricultural farmscapes. Specifically, this work aimed to: (1) document feeding of the monarch butterfly, insect pollinators and stink bug parasitoids on milkweed nectar in the field, (2) determine the impact of strategic placement of milkweed nectar provision on parasitism rates of stink bugs in cotton, and (3) and examine the ability of the milkweed insectary habitat to reduce stink bugs below economic threshold in cotton. In 2009, plots of cotton (22.9 m long by 1.83 m [16 rows] deep) were established along the interface of a peanut-cotton farmscape. Each treatment, cotton with a milkweed insectary habitat and cotton control, was randomly assigned to a plot within a block for each of 4 blocks in a randomized complete block (RCB) design (2 treatments × 4 replicates). In 2010, there were 5 treatment replicates. For the insectary habitat, 25 potted flowering milkweed plants were placed 1.2 m apart along the edge of a cotton plot. Stink bugs were sampled each week for 5 weeks during stink bug colonization of cotton. For each sample, all plants within a 1.83-m length of row were shaken over a drop cloth and visually checked for these bugs. Over the 2-yr study, monarch butterflies, insect pollinators and stink bug parasitoids readily fed on milkweed nectar in these insecticide-free habitats. For the first year of the study, addition of the milkweed insectary habitat adjacent to cotton increased parasitism of N. viridula by T. pennipes by close to 5-fold relative to control cotton. In 2010, combined parasitism of N. viridula, C. hilaris, and a leaffooted bug, Leptoglossus phyllopus, by T. pennipes was at least 3-times greater in plots with a milkweed habitat compared to control cotton. For each year of the study, differences in parasitism rates between treatments were not due to differences in bug density. In 2009, there was some indication that this sole management strategy can help maintain stink bugs below economic threshold in this crop. However, complimentary management strategies, such as use of selective insecticides and trap cropping, may also need to be incorporated in these farmscapes to continually suppress these pests below economic threshold throughout the growing season. In conclusion, provision of a milkweed insectary habitat at the crop-to-crop interface in peanut-cotton farmscapes aided insect pollinator and monarch butterfly conservation as well as increased the rate of stink bug adult parasitism in cotton.

Technical Abstract: The flowers of milkweed species can produce a rich supply of nectar, and therefore, planting an insecticide-free milkweed habitat in agricultural farmscapes could possibly conserve monarch butterflies, bees and other insect pollinators, as well as enhance parasitism of insect pests. In peanut-cotton farmscapes in Georgia, stink bugs, i.e., Nezara viridula, Euschistus servus, and Chinavia hilaris, develop in peanut and then disperse at the crop-to-crop interface to feed on fruit in cotton. Strategic placement, in time and space, of a milkweed habitat at these crop-to-crop interfaces may lead to successfully increasing biocontrol of stink bugs in these agricultural farmscapes. Specifically, this work aimed to: (1) document feeding of the monarch butterfly, insect pollinators and stink bug parasitoids on milkweed nectar in the field, (2) determine the impact of strategic placement of milkweed nectar provision on parasitism rates of stink bugs in cotton, and (3) and examine the ability of the milkweed insectary habitat to reduce stink bugs below economic threshold in cotton. In 2009, plots of cotton (22.9 m long by 1.83 m [16 rows] deep) were established along the interface of a peanut-cotton farmscape. Each treatment, cotton with a milkweed insectary habitat and cotton control, was randomly assigned to a plot within a block for each of 4 blocks in a randomized complete block (RCB) design (2 treatments × 4 replicates). In 2010, there were 5 treatment replicates. For the insectary habitat, 25 potted flowering milkweed plants were placed 1.2 m apart along the edge of a cotton plot. Stink bugs were sampled each week for 5 weeks during stink bug colonization of cotton. For each sample, all plants within a 1.83-m length of row were shaken over a drop cloth and visually checked for these bugs. Over the 2-yr study, monarch butterflies, insect pollinators and stink bug parasitoids readily fed on milkweed nectar in these insecticide-free habitats. For the first year of the study, addition of the milkweed insectary habitat adjacent to cotton increased parasitism of N. viridula by T. pennipes by close to 5-fold relative to control cotton. In 2010, combined parasitism of N. viridula, C. hilaris, and a leaffooted bug, Leptoglossus phyllopus, by T. pennipes was at least 3-times greater in plots with a milkweed habitat compared to control cotton. For each year of the study, differences in parasitism rates between treatments were not due to differences in bug density. In 2009, there was some indication that this sole management strategy can help maintain stink bugs below economic threshold in this crop. However, complimentary management strategies, such as use of selective insecticides and trap cropping, may also need to be incorporated in these farmscapes to continually suppress these pests below economic threshold throughout the growing season. In conclusion, provision of a milkweed insectary habitat at the crop-to-crop interface in peanut-cotton farmscapes aided insect pollinator and monarch butterfly conservation as well as increased the rate of stink bug adult parasitism in cotton.