European chafer beetles (Rhizotrogus majalis, Order: Coleoptera) are one of the most damaging pest of turfgrasses, horticultural such as blueberries and strawberries, and field crops including corn, potatoes and small grains. Adult beetles are brownish in color and about 0.5 inch long whereas mature larvae are “C” shaped, about 1.0 inch long, creamy white in color with brown/orange head capsule and three pairs (six) prominent legs.
European chafer beetles generally take one year to complete their life cycle that consists of four life stages such as eggs, larvae (grubs), pupae and adults. Adult beetles generally emerge in the mid June through early July from pupae every year and always swarm in mating flights at warm dusks. After mating, each female lays about 50 eggs 4-5 inches deep in the cool and moist soil. These eggs hatch within 3-4 weeks into small larvae called grubs, which immediately starts feeding on the roots turfgrass and other host plants. While feeding, grubs develop through three instars/stages that continue feeding until the ground freezes. Once soil starts freezing, grubs move deep in the soil for overwintering. These overwintering grubs stop feeding during winter or until soil begin thawing in March through April. In April overwintering grubs migrate near to the soil surface where they resume feeding on the host roots. While feeding grubs grow in size, mature and pupate in mid- May in the soil. After 3-4 week, the new generation adults start emerging from pupae and life cycle continues.
Although, the life cycle of European chafer beetle consists of eggs, larvae (grubs), pupae and adults, only grubs can cause damage by feeding on the roots of turf grass and other host plants. Adult do not feed on plants but their females after mating lay eggs in the soil. After hatching from eggs in mid-July, first instar small grubs immediately start feeding on the roots of turfgrass and continue feeding until soil begins freezing in November. Feeding activity of grubs stops during winter but it resumes again when temperature rises in the spring and it continues until they form pupae. These grubs are cold tolerant and known to feed on grass roots even grass is covered with ice/snow. Although the third stage grubs of european chafer beetles cause a severe damage to turf during both fall and spring seasons, its severity is masked due to presence of high moisture in the soil during these seasons. However, the severity of damage by this pest can be easily noticed under dry weather conditions. The symptom of severe damage by chafer grubs include brown and dying patches of turfgrass throughout the golf courses and home lawns. The most important sign of presence of european chafer beetle grubs in the lawn is that the grub infested areas are destroyed by digging activity of animals such as raccoons and skunks and birds that are looking for grubs to feast on them. Another sign of heavy infestation by european chafer grubs is that the infested grass in the lawn feel “spongy” due to tunnelling by grubs underneath the grass.
Use of chemical pesticides is generally restricted on the golf courses, home lawns and recreational parks due to their detrimental effects on humans, animals and environment. Therefore, beneficial entomopathogenic nematodes can serve as a safe and environment friendly alternative to pesticides in controlling European chafer beetles and maintaining the aesthetic value of golf courses and lawns. Beneficial entomopathogenic nematodes are insect parasitic nematodes that are currently used as effective biological control agents to control soil-dwelling pests of many agricultural and horticultural crops. Of the several commercially available entomopathogenic nematodes, beneficial Heterorhabditis bacteriophora nematodes have been proved to be effective against European chafer beetle grubs. The best time to apply these beneficial nematodes is mid-July through early August because during this time both the first and second instar grubs are actively feeding on grass roots and these stages are known to be very susceptible to beneficial nematodes (Grewal et al., 2005; Koppenhofer et al., 2004). Beneficial entomopathogenic Heterorhabditis bacteriophora nematodes are very effective in killing young grubs of european Chafer beetles when they are applied at the rate of 23000 nematodes per square foot area between the middle of July and early August.
Grewal, P.S., Koppenhofer, A.M., and Choo, H.Y., 2005. Lawn, turfgrass and Pasture applications. In: Nematodes As Biocontrol Agents. Grewal, P.S. Ehlers, R.-U., Shapiro-Ilan, D. (eds.). CAB publishing, CAB International, Oxon. Pp 147-166.
Koppenhofer, A.M., Fuzy, E.M., Crocker, R.L., Gelernter, W.D. and Polavarapu, S. 2004. Pathogenicity of Heterorhabditis bacteriophora, Steinernema glaseri, and S. scarabaei (Rhabditida : Heterorhabditidae, Steinernematidae) against 12 white grub species (Coleoptera : Scarabaeidae). Biocontrol Science and Technology. 14: 87-92.