Milkweed patch size effects on monarch butterfly oviposition within Iowa prairies and roadsides.

Monday, February 26, 2018 - 4:10pm
Event Type: 

Teresa Blader, Iowa State University, Department of Entomology

M.S. defense seminar.

Abstract. Monarch butterfly, Danaus plexippus, overwintering populations in Mexico have declined over the past 15 years. One reason attributed to this decline is the loss of milkweed (Asclepias spp.) in corn and soybean fields due to growers’ widespread use of herbicide-tolerant crops. Roadsides and prairies provide an important milkweed resource for ovipositing adults and hungry caterpillars and could compensate for this loss. Conservationists are seeking answers about existing milkweed populations and what adjustments need to be made to reach monarch conservation goals. If patch size is influential in drawing in monarchs for oviposition, then optimal patch size could help maximize egg and caterpillar production. To test this hypothesis, four gravel roadsides in Story and Boone Counties, Iowa were monitored for milkweed with GPS units. Over 14,000 milkweed stems were mapped and examined for eggs and larvae. These data were spatially analyzed in ArcMap 10.4, GeoDa, and R to measure the correlation between plant number in an area and the corresponding numbers of eggs and larvae. A similar study was conducted with transplanted common (A. syriaca) and swamp (A. incarnata) milkweed in prairies and examined weekly for eggs and larvae over three years. Results from both studies are used to discuss if there is an “optimal” patch size for attracting females as well as what role milkweed characteristics and surrounding landscape play in influencing female monarch oviposition.