Don’t get foiled by the flea beetle

1) Fig. 1: Eggs are oblong, approximately 1.0 mm in length, and creamy-white. 

2) Fig. 2: Adults are shiny black, and about 9 mm in length with a reddish head.

3) Fig. 3: Adult males tend to be smaller than adult females.

4) Fig. 4: Adults feed on the upper and lower leaf surfaces causing leaf skeletonization.

5) Fig. 5: Severe damage to plants reduces aesthetic quality and marketability.

The redheaded flea beetle, Systena frontalis, has emerged as a major insect pest in nursery production systems. Adults feed on many different ornamental plants; however, based on our experience and feedback from producers, Itea sp., Hydrangea sp., Cornus sp., and Weigela sp., are highly susceptible to redheaded flea beetle adults. In fact, specific cultivars tend to be more susceptible, including Itea virginica ‘Little Henry,’ Hydrangea paniculata ‘Vanilla-Strawberry’ and ‘Bobo,’ Cornus sericea ‘Kelseyi,’ and Weigela florida ‘Fine Wine.’ We have been conducting studies on redheaded flea beetle for five years at Loma Vista Nursery, one of the largest nursery operations in Kansas, and have obtained information related to biology and management.

Biology

The life cycle of the redheaded flea beetle consists of an egg, larva, pupa, and adult.

Eggs are oblong, approximately 1.0 mm in length, and creamy-white (Figure 1). Larvae are 5-10 mm long, creamy white, and have a brown head capsule when mature. The last body segment has a fleshy projection that curves upward, with hairs on the end. There are three larval instars. Larvae are located belowground in the growing medium/soil, and feed on plant roots. However, the larvae are less of a problem to plants than the adults. There is minimal information available on the pupal stage.

Adults are shiny black, and about 9 mm in length with a reddish head (Figures 2 and 3). Adult males tend to be smaller than adult females. Females lay eggs individually. Adults possess an enlarged hind femur that allows them to jump/hop similar to a flea—hence the common name. Adults feed on the upper and lower leaf surfaces causing leaf skeletonization and creating holes in leaves (Figures 4 through 6). In addition, adults deposit black fecal material on leaves during feeding.

On Itea virginica ‘Little Henry,’ adults tend to feed on the new growth where leaves are folded and pointing upward. Severe damage to plants reduces aesthetic quality and marketability. Adults can also feed on many weeds commonly associated with nursery production including common lambsquarters (Chenopodium album), pigweed (Amaranthus sp.), smartweed (Polygonum sp.), and velvetleaf (Abutilon theophrasti) among several other species. Adults may be present from June through November with possibly two to three generations per year; however, this is contingent on temperature and availability of suitable host plants. The number of generations in Kansas has not been determined. Based on experiments in which field containers of plants were collected and placed into a greenhouse (Figure 7), we have quantitatively shown that redheaded flea beetles emerge as adults from containers (Figure 8). From May 21 to June 18, 2018, we collected 10 redheaded flea beetle adults from 30 containers associated with I. virginica and H. paniculata plants.

Management

Weed removal from within the nursery, including containers, will help reduce potential food sources of redheaded flea beetle adults. Redheaded flea beetle adults may enter nurseries from surrounding vegetation; especially if the plants or weeds are a viable host. It is important to develop and implement an aggressive scouting program by monitoring for adults weekly, focusing on plants that are highly susceptible to redheaded flea beetle adults, and then conducting spray applications accordingly. Apply insecticides weekly when adults are active. We have found, in our efficacy trials, the following insecticides to be effective in protecting plants from damage caused by redheaded flea beetle adults: acetamiprid (TriStar), dinotefuran (Safari), and cyfluthrin (Tempo). Thorough coverage of all plants is important, as well as, the growing medium/soil as redheaded flea beetle adults may be able to sense changes in air pressure. Consequently, the adults will hop off plant leaves and land on the surface of the growing medium/soil (Figure 9) or the leaves of adjacent plants. Systemic insecticides can be used; however, adults still have to feed on plant leaves to be negatively affected, and depending on numbers, may still cause substantial aesthetic damage.

Author’s note: We want to thank Michael Sellers, Duane Huss, Thomas Minter and Lyndsi Oestmann of Loma Vista Nursery in Ottawa, Kansas, for their assistance and allowing us to conduct research on the redheaded flea beetle.

Raymond A. Cloyd is a professor and Nathan J. Herrick is a research associate in the Department of Entomology at Kansas State University.