–by Dr. Raymond Cloyd
If you want to see the destructive ability of an extensive population of elm leaf beetle, Pyrrhalta luteola, larvae; there are three large Siberian elm (Ulmus pumila) trees located on the south-side of Old Claflin Road on the campus of Kansas State University (Manhattan, KS) that have been heavily fed upon by the larval stage to the point that nearly all the green content of the leaves has been removed (Figure 1).
Fig 1. Feeding damage caused by elm leaf beetle larvae (Author–Raymond Cloyd, KSU
In fact, the populations are so extensive that adults and larvae are present simultaneously (Figure 2).
Fig 2. Elm leaf beetle adult and larvae on tree trunk (Author–Raymond Cloyd, KSU)
In addition, larvae are accumulating and pupating on the trunk (Figure 3)
Fig 3. Elm leaf beetle pupae in the crevices of the tree trunk (Author–Raymond Cloyd, KS
and at the base of the trees (Figures 4 and 5). As of this past weekend (July 14-15), adults were migrating upward to feed (on what is left). The infestation is almost ‘biblical’ in proportion…it is absolutely AWESOME (from an entomological stand-point).
Fig 4. Elm leaf beetle larvae and pupae at the base of a tree (Author–Raymond Cloyd)
Fig 5. Close-up of elm leaf beetle larvae and pupae at the base of a tree (Author–Raymond Cloyd, KSU)
Elm leaf beetle adults are 1/4 inches in length, yellow to dull-green, with a black stripe on each wing cover extending the entire length of the abdomen. The head and thorax have distinct black spots (Figure 6).
Figure 6. Adult elm leaf beetle (Author–Raymond Cloyd, KSU)
Adults feed between the major veins resulting in leaves having a ‘shot hole’ (similar to ‘buckshot’) appearance. The larvae are 1/2 inch long and yellow, with two lines of black spots on the back (Figure 7).
Fig 7. Elm leaf beetle larvae on tree trunk (Author–Raymond Cloyd, KSU
They feed on the underside of leaves causing the leaves to appear skeletonized, and eventually turning brown (Figure 8). The larvae normally migrate down the trunk of trees and tunnel into or reside on the soil surface to pupate, with adults emerging later on that will migrate upward on the tree trunk. There are two generations per year in Kansas. A contact insecticide can be applied when adults and larvae are feeding on leaves. However, thorough coverage of leaf undersides is important as this is where the adults and larvae tend to feed.
Fig 8. Feeding damage to elm leaf caused by elm leaf beetle larvae (Raymond Cloyd, KSU)