–by Dr. Raymond Cloyd
We are seeing damage on elm (Ulmus spp.) trees caused by the larvae and adults of the European elm flea weevil (Orchestes alni). Larvae are cream-colored, legless (Figure 1), and located in the mines of leaves. Adults are 3 mm (0.11 inches) in length, red-brown, with black spots or markings on the abdomen or wing covers (Figure 2).
Fig 1. European elm flea weevil larva (Auth–Raymond Cloyd, KSU)
Fig 2. Adult European elm flea weevil (Auth–Raymond Cloyd, KSU)
The mouthpart is shaped-like a snout (Figure 3)
Fig 3. European elm flea weevil adult (note the snout-like mouth) (Auth–Raymond Cloyd, KSU)
since they are weevils and 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 hatch from eggs and tunnel through the leaf as they feed, creating serpentine-like mines that enlarge as larvae mature (Figure 4).
Fig 4. Serpentine mines created by European elm flea weevil larvae (Auth–Raymond Cloyd, KSU)
Larvae eventually transition into a pupal stage, and then adults emerge in May through June. Adults primarily feed on leaf undersides creating small holes on young leaves (Figure 5).
Fig 5. Feeding damage caused by European elm flea weevil adult (Auth–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 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.
Management of European elm flea weevil involves maintaining tree health by implementing proper watering, mulching, pruning, and fertilizing practices Insecticides can be used to minimize damage; however, insecticides are difficult to apply to large trees. Contact insecticides must be applied May through June to suppress adult populations. Be sure to 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 leaves. If damage is not extensive, especially on large trees, then there is no reason to apply insecticides.