Monarch Butterfly in Kentucky and Early Season Pest Management at Way-stations

Monarch Butterfly Sightings in 2015

According to this monarch butterfly migration page, the first reported sightings of monarch butterflies (Figure 1) in Kentucky were May 12 in Danville, May 13 in Lexington, and May 24 in Scottsville.

Figure 1. Monarch butterfly. (Photo: Lee Townsend)

Figure 1. Monarch butterfly. (Photo: Lee Townsend)

Previous monarch research by UK entomologists documented the presence of many adults in May but little evidence of eggs. Few individuals were seen during June but the butterflies, their eggs, and larvae were abundant in July.

Milkweeds in Monarch Butterfly Way-Stations May Need Some Protection

Defensive chemicals in milkweed plants protect them from most insect herbivores. However, a handful of aphids, beetles, and caterpillars can deal with the plant’s cardiac glycosides and milky, sticky sap. In sufficient numbers, these pests can eat a significant amount of foliage, or they can affect plant vigor and perhaps plant attractiveness to monarchs. Fortunately, most of these are minor concerns, so management can be limited to a watchful eye and hand-picking to remove them. Here is a look at common aphid species that feed on milkweed.

Aphids Infesting Milkweed

Several species of aphids can infest milkweed. Colonies develop when winged females land on plants and deposit small numbers of live young on tender terminal foliage. Clusters of these small, soft-bodied insects build up on lower surfaces of developing leaves or tender new stems where their numbers steadily increase. Sap removal while feeding can lead to deformed leaves and stems or even death of plant terminals.

In some cases, ants can be seen on infested plants. They tend the aphids (Figure 2) to collect their nutrient-rich waste for their colonies and in turn protect aphids from predators.

Lady beetles and other natural enemies eat aphids, but the reproductive capacity of these small, soft-bodies insects generally outpaces consumption.

At least 5 aphid species of various colors (black, green, and red) can be found on milkweed, usually early and again late in the growing season. Aphids can cover the upper growth damaging growing tips, leaves, and pods (Figure 3).

Figure 2. Aphids being tended by ants. (Photo: Lee Townsend, UK)

Figure 3. The distinctive oleander aphid is easily noticed; other species are more cryptic. (Photo: Lee Townsend, UK)

Figure 3. The distinctive oleander aphid is easily noticed; other species are more cryptic. (Photo: Lee Townsend, UK)



Mechanical control (crushing, etc.) or sprays of insecticidal soap can provide satisfactory control. Winged aphids are active over most of the growing season so new infestations can start at any time. Weekly checking of terminal foliage during the growing season is the main way of keeping these insects from reaching damaging levels.

By Lee Townsend, Extension Entomologist


Posted in Beneficial Insects