By Estella Crosby, Summer Research Assistant, OMAFRA
Garden fleahopper (Microtechnites bractatus) is an occasionally severe pest of lavender and potentially other perennial members of the mint family, especially when grown over black plastic mulch where warmer temperatures promote faster development and produce more generations per year. Garden fleahoppers have also been observed in higher numbers in angustofolia cultivars than lavandin cultivars.
Nymphs of garden fleahopper progress through five instars (stages), which are pale green in the first four instars and darker green in the final instar. The third to fifth instars also have black spots. Adults are black with prominent hind legs, which are used for jumping (Figure 1). Both the jumping habit and the appearance resemble flea beetles, but the antennae of fleahoppers are longer than the body, while flea beetle antennae are much shorter than the body. Adult fleahoppers are about 2 mm long.
Figure 1: Garden Fleahopper nymph (left) and adult (right)
Garden fleahoppers are in the Hemiptera or True Bug Order of insects. Eggs are inserted into the stems of plants, which is how they overwinter. Nymphs hatch in May and progress through the five instars at a rate of about one instar per week. Adult fleahoppers mate and females lay eggs on plant surfaces. Eggs hatch within two weeks to continue the cycle. There are several overlapping generations per year, with all stages present on the same plant beginning in early summer. As seen in Figure 2, there is a large flux in the number of insects present from week to week because of the multiple generations present. However, the number of garden fleahoppers present on lavender can vary from none being observed to over 50 being observed on a piece of white paper (see scouting technique below) at a different plant a few feet away. This can lead to some plants having severe damage while others in the same area have minimal damage.
Figure 2: Average number of garden fleahoppers observed per scouting paper
Garden fleahoppers lead to white flecking on the leaf surface beginning with the leaves in the centre of the canopy (Figure 3). At the beginning of the summer, the damage is mainly on the tender tips of the leaves as the nymphs of the garden fleahoppers are small and cannot yet damage the tougher parts of the plants. However, as the summer progresses, and the instars grow, the damage is more spread out. Plants can tolerate considerable damage, but populations have been known to grow and severely weaken plants by late summer. Once the damage becomes obvious from a distance, control measures may be warranted. Since nymphs and adults are tiny and difficult to see within the canopy, they are best identified by shaking the plant vigorously over a white sheet of paper. It is best to have the white sheet of paper on a firm surface like a clipboard and to put it between the ground and the lowest part of the plant before shaking (Figure 4). Shake with both hands and then quickly inspect the paper as garden flea hoppers can jump away very quickly. Make sure the paper is completely free of debris and insects before moving onto the next plant.
Figure 3: Garden fleahopper damage. Note the white flecking on the lower leaves
Figure 4: Garden fleahopper scouting technique.
There are a few options for the management of this pest in herbs. Insecticides used to control other true bugs like four-lined plant bugs or tarnished plant bugs may suppress populations if applied multiple times during the growing season. The youngest nymphs are more likely to be controlled by insecticides.