- Scientific Name: Rhizotrogus majalis (Razoumowsky) (commonly Amphimallon in Europe - previous names are: Amphimallon rufescens Latreille, Amphimallus majalis Razoumowsky, Rhizotrogus majalis (Razoumowsky), and Rhizotrogus rufescens Latr) [Phylum Arthropoda: Class Insecta: Order Coleoptera: Family Scarabaeidae].
- Common Names: European chafer, European cockchafer, hanneton européen, hanneton europeen, Blatthornkäfer
- Climatic Zone: Temperate
- Geographic Distribution: This European pest was first detected in the United States in Newark, NY in 1940. Since then the pest has spread into Connecticut and upper New York, west across northern Ohio and south from West Virginia across Maryland. A population is well established in eastern Michigan. In Canada, this pest occupies the southern parts of Ontario and Quebec provinces. [EUROPE: Austria, Belgium, Corsica, Czechoslovakia, France, Germany, Italy, Luxembourg, Sardinia, Spam, Switzerland, Yugoslavia]
- Damaging Stage: larvae
- Hosts: The grubs feed on a wide variety of plant roots and organic matter in the soil. They are known to feed on the roots and thatch of all cool season turfgrasses, clovers, small grain crops and weeds. The adults apparently do not feed.
- Damage Symptoms: Typical grub damage of thin turf, wilting and death in irregular patches can be found in the fall and early spring.
- Description of Stages: This pest has stages typical of an annual white grub.
Eggs: The freshly laid eggs are an oval shape, approximately 0.73x0.49mm, and a shiny, milky white color. After absorbing water, the eggs become dull grey and swell to 2.0x2.7mm.
Larvae: The first instar larvae are about 4mm long and these grow to approximately 17mm when fully grown third instars. All three instars are typical C shaped white grubs but these can be identified by the raster which has two parallel rows of bristles which diverge laterally at the anus. These grubs are slightly smaller than the June beetles. Phyllophaga grubs have two parallel rows of bristles on the raster which do not diverge at the anus.
Pupae: The pupa looks like most scarab pupae but is slightly larger than that of the Japanese beetle and smaller than the Phyllophaga.
Adults: The adults look much like some of the light colored June beetles. However, the European chafer is 13 14mm long, shorter than most June beetles, and the wing covers have distinct longitudinal grooves (striatae). The most distinctive characteristic is the absence of a tooth on the tarsal claw of the middle leg. The Phyllophaga have a distinct tooth.
- Life Cycle and Habits:
The adults begin emerging from the pupal cells in mid-June and continue mating and ovipositing until late July. Most activity occurs from the last week of June through the second week of July. The adults emerge at sundown and fly to nearby trees and shrubs silhouetted against the sky. Here, large numbers fly, with a considerable buzzing noise, for 20 to 35 minutes. Thousands may congregate on a single tree. When the sky is truly dark, the adults settle on the foliage and begin copulation. Copulation continues in mass until daybreak when the adults return to hide in the soil. Cool or rainy nights greatly reduce flight and mating activities. Apparently adults may return to trees several times for mating, but eventually females dig into the soil to lay eggs.
Each female lays 15 to 20 eggs in 2 to 5 days. The eggs are usually laid singly in compacted cells of soil 2 to 6 inches deep. The eggs swell as they absorb soil moisture and hatch in about two weeks. The first instar may remain deep in the soil if surface soil moisture is low. Eventually, the young larvae move to the surface and feed on organic matter, including plant roots. If food is sufficient, the first instar matures in about three weeks and the second instar takes about four more weeks to mature. This pest moves up, down and sideways depending upon soil moisture and food availability. The third instars feed for a period in the fall before moving down for the winter.
The European chafer grubs may feed longer in the fall than many other species before moving down and it is one of the first to return to the surface in the spring, often in March. In thick sod and under heavy snow cover, grubs may remain in the upper one to two inches of soil during the winter. Pupation occurs in mid-May, 2 to 6 inches in the soil.
- Control Approaches:
Cultural Control - Plant Quarantines - The European chafer is a serious pest of nursery stock, therefore, care in only planting stock certified free of this and other root pests will help further reduce their spread. Other than allowing the soil to dry out during the time eggs are developing, no other cultural controls have much influence on this turf pest.
Natural Control - Diseases - A milky disease specific to the European chafer naturally reduces larval populations. The milky disease which infects Japanese beetle larvae is relatively ineffective against this insect. The naturally occurring soil fungus, Metarrhizium spp., and insect parasitic nematodes, usually Steinernema spp. and Heterorhabditis spp., also contribute to population limitation.
Biological Control - Diseases - No commercial preparation of the milky disease specific to this grub is available. The steinernematid nematodes, S. glaseri and S. feltiae, have been marketed for control of European chafer and other grubs. These nematodes have not performed well or consistently. Commercial formulations of the naturally occurring fungus, Beauveria bassiana JW-1, are also labeled for control of this grub species, but again, results have been variable.
Chemical Control - Insecticides -
Preventive Treatments. Insecticides with long residual activity (e.g., 80 to 120 days) can produce excellent grub control with a single application made in May, June, July or August. Preventive treatments are most warranted where the risk of grub infestation is greatest. Recent research has shown that turf areas that have experienced a damaging grub infestation are more likely to experience a reoccurring damaging infestation. Likewise, certain golf course areas and lawns in neighborhoods often have reoccurring infestations. These are likely candidates for preventive treatments.
Curative Treatments. Insecticides are most effective when small size grubs are the target. First instar European chafer grubs are present from mid-July through mid-August. Applying an insecticide at this time, followed by sufficient irrigation to move the insecticide to the grubs usually yields satisfactory results. First instar grubs molt into second instars that feed from mid-August through mid-September. These medium sized larvae are also quite susceptible to control, but if not controlled, turf damage may begin to appear in mid-September. From late September through November, European chafer grubs reach the third instar stage and are 40 to 60 times the body weight of the newly hatched, first instars. By this time, significant damage may be evident and skunks and racoons often dig up infested turf to feed on the grubs.
Rescue Treatments. Most insecticide applications made in late September through November yield poor control of third instar grubs. At this time, insecticides known to have rapid action and are least affected by thatch binding can be effective, but substantial irrigation may be needed to move the control product to the soil-thatch interface. In March and April, European chafer grubs return to the upper soil level to briefly feed. Though grub damage may be evident at this time, skunk and racoon digging is usually the major problem.
Grub infestations should be discovered as early as possible by monitoring, accurate identification and mapping of infested areas. Since European chafer adult are not highly attracted to lights or black light traps, the standard golf course cup cutter is a convenient tool to survey for infestations in golf courses, sports turf and home lawns. If care is exercised, sampling can be done with minimal damage to the turf. Once removed, samples can be examined carefully on the spot. Each soil and turf core is placed back in the hole made by the sampler. The sample does not have to be completely torn apart to determine the number of grubs present. If the soil is dry, it is advisable to add water to the sample hole before replacing the sample to improve the turf survival.
The standard cup cutter is 4-1/4 inch in diameter. Therefore, to convert the number of grubs found per sample to the number of grubs per square foot, multiply the average per sample by a factor of 10.15.
A hand lens is a most useful tool for identifying insects in the turfgrass environment. Use of a hand lens also projects a professional image to those nearby. Generally, lenses of 10X are adequate for most purposes, including identification of white grub species.
Many books and extension publications on grub management often mention “population thresholds.” Thresholds are the numbers of pest insects present in a given area (usually per square foot) that warrant control. The idea behind using thresholds is to reinforce the IPM principle that application of a pesticide is not always warranted simply if pests are present. Pests must be present at populations high enough to eventually cause damage.
The generally accepted level for European chafer is 6 to 10 grubs/ft2, before control is warranted. However, well maintained turfgrass with regular irrigation and fertilization can “tolerate” much higher grub populations. On the other hand, moles, skunks and racoons often find less than six grubs/ft2 sufficient to dig up the turf in search of them.
Thresholds must be adjusted for each turf situation. For golf courses, damage in roughs is more tolerable than damage in fairways, and damage in fairways is more tolerable than damage on tees and greens. Likewise, some course or home owners demand high turf standards while others may tolerate some periodic, localized damage.