–by Raymond Cloyd — Horticultural Entomology
We are seeing damage on elm, Ulmus spp., trees caused by larvae of the European elm flea weevil, Orchestes alni. The larvae are approximately 4 mm (0.16 inches) in length, cream-colored, legless, wrinkled in appearance (Figures 1 and 2)
Figure 1. European elm flea weevil larva (Raymond Cloyd, KSU)
Figure 2. Close-up of European elm flea weevil larva (Raymond Cloyd, KSU)
and located in leaf mines. Adults, which will be present later in the growing season, are 3 mm (0.11 inches) long, red-brown, with black spots or markings on the abdomen (Figure 3).
Figure 3. Adult European elm flea weevil (Raymond Cloyd, KSU)
Their chewing mouthparts are located on the end of a snout-shaped structure that protrudes from the head. The hind legs are thickened and enlarged, which allows the adults to jump when disturbed. Adults are initially active
in May, and after mating, females lay eggs in the large mid-veins of new leaves. Larvae emerge (eclose) from eggs and tunnel through the leaf as they feed, creating serpentine-like mines that enlarge as larvae mature (Figure 4).
Figure 4. Serpentine mines created by European elm flea weevil larvae (Raymond Cloyd, KSU)
). Larvae eventually transition into a pupal stage, and then adults emerge (eclose) from May through June. Adults primarily feed on leaf undersides creating small holes on young leaves (Figure 5).
Figure 5. European elm flea weevil adult feeding damage (Raymond Cloyd, KSU)
Feeding damage caused by larvae and adults will not kill an elm tree; however, extensive feeding damage may ruin the aesthetic appearance. Adults overwinter under loose bark and in leaf litter located under previously infested elm trees. There is one generation per year in Kansas. Nearly all elm species are susceptible to feeding by the European elm flea weevil; especially Siberian elms (Ulmus pumila) and certain elm hybrids with Asian parentage.
European elm flea weevil management involves keeping elm trees healthy by implementing proper watering, mulching, and pruning practices. Insecticides may be used to minimize damage; however, insecticides may be difficult to apply to large elm trees. Contact insecticides should be applied from May through June to suppress adult European elm flea weevil populations. Always read the insecticide label carefully to ensure that “weevils” are listed. Thorough coverage of leaf undersides is important because adults tend to feed on the undersides of elm leaves. If damage is not extensive, especially on large elm trees, then there is no reason to apply insecticides. In most cases, the application of an insecticide is not warranted or the insecticide application will be too late to negatively affect the European elm flea weevil population.
For more information regarding European elm flea weevil management, contact your county extension agent or state extension specialist.