Abstract Detail



Ecology

Deecher, Elizabeth [1], Billman, Brittany [2], Siryani, Nijmih [2], Rollinson, Emily [2].

Effects of Invasive Aphids on Common Milkweed Ecology.

Common milkweed (Asclepias syriaca) is frequently found on roadsides and open fields, but much of their habitat is being lost to human development. Although cardenolides within milkweed make it toxic and distasteful to larger herbivores, this is not effective against some insects, including the invasive oleander aphid (Aphis nerii) targets milkweed species and can potentially weaken these plants. This may have downstream effects on other insects relying on milkweed, including the declining monarch butterfly (Danaus plexippus), which uses milkweed as a host plant. We surveyed milkweed populations to determine overall prevalence of the invasive aphid and identify possible effects of the aphids on milkweed and monarchs.

In Fall 2018, we surveyed Danaus plexippus and Aphis nerii abundance in 23 populations of Asclepias syriaca in northeastern Pennsylvania, USA. In each milkweed population, we measured the size of the milkweed population, density of aphids on milkweed leaves, and abundance of monarch caterpillars on each plant and across the entire population. This survey allowed us to document spatial variation in milkweed population size and in insect populations on these plants. In Summer 2019, we conducted regular monitoring of milkweed plants and associated insects in nine A. syriaca patches in northeastern Pennsylvania. In each patch, ten plants were tagged and measured weekly for height and number of leaves. Density of aphids was recorded on leaves and fruits, as well as abundance of monarch caterpillars.  
Of the 23 populations surveyed in 2018, 5 had monarch caterpillars. We found no significant difference in aphid abundance between monarch-inhabited and uninhabited milkweed populations, nor between monarch-inhabited and uninhabited individual plants. In 2019, there was a significant difference in monarch abundance among patches. All but one milkweed patch had aphids present at some time during the sampling season. Although overall differences in aphid abundance among patches were not statistically significant, one patch had an order of magnitude higher aphid density than the other populations. Aphid abundance peaked in mid- to late- July, after the milkweed had flowered and produced fruits; monarch caterpillars also peaked in abundance during this time. Aphid density did not appear strongly related to plant height, leaf production, or fruit production. These results suggest that aphids may not have downstream effects on the availability of milkweed as a host for monarchs, and highlight a need to identify factors driving variation in insect abundance in milkweed populations.


1 - Penn State University, Department of Entomology, 501 ASI Building, University Park, PA, 16802, USA
2 - East Stroudsburg University, Department Of Biological Sciences, 200 Prospect Street, East Stroudsburg, PA, 18301, United States

Keywords:
Asclepias syriaca
Aphis nerii
Danaus plexippus
Plant-Animal Interactions
biological invasions.

Presentation Type: Poster Time and date to be determined
Number: PEC012
Abstract ID:497
Candidate for Awards:None


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