Masked Chafers

Masked chafers are beetles that have larvae, called white grubs, which can attack managed turf. They are natives of North America. The southern masked chafer is most common in the southern states and has been collected from Central and South America. It has been recently reported as a more common pest in southern Ohio, Indiana, Illinois, Iowa and Nebraska. The northern masked chafer is commonly a pest in the Kentucky bluegrass and tall fescue growing regions from New England across to Illinois. Specimens have been collected from Maine across to Nebraska.

Hosts

The southern masked chafer grubs commonly attack turfgrasses in the transition zones (Kentucky bluegrass and tall fescues) and in southern bermudagrass areas. The northern masked chafer grubs usually attack cool season turf, especially if Japanese beetle grubs have been suppressed. Additionally, both species attack the roots of field crops such as wheat, oats and corn. The adults do not feed.

Damage Symptoms

Turf begins to show drought stress in late summer into fall or spring and does not rapidly recover after rain or irrigation. Heavy infestations result in turf dying in irregular patches. Birds, skunks, raccoons and opossums commonly dig up turf around the dead patches. Moles may tunnel extensively where grub populations are high. Infested turf feels spongy under foot and is easily lifted because of the absence of roots. The adults do not feed on ornamental plants or turf.

Northern masked chafer grub	White grub damage

Description of Stages

Masked chafers have a typical annual scarab life cycle with a complete metamorphosis. Determining the species of larvae and adults of all of the Cyclocephala is difficult without the assistance of a taxonomist.

• Eggs: The eggs are oval when laid and are about 1/16 inch (1.7 mm) long by 3/64 inch (1.2 mm) wide. These pearly white eggs absorb moisture from surrounding soil and increase to 2.1 mm in diameter and have a nearly spherical shape.
• Larvae: First instars are about 3/16 inch (4.5 mm) long at hatching and reach 1 inch (22 to 25 mm) when maturing as third instars. The mouthparts must be dissected to distinguish between the northern and southern masked chafers. The larvae have the irregular pattern of bristles on the raster, which is typical of all Cyclocephala larvae.
• Pupae: The 5/8 inch (17 mm) long by 1/4 inch (8 mm) wide pupae are first creamy white and gradually change to reddish-brown just before the adult emerges. Female and male pupae can be separated by looking at the lower surface of the ninth abdominal segment. The males have a pair of conspicuous lobes, while females have the segment partially divided below the genital pore.
• Adults: The adults are a dull dark yellow-ocher and have darker brownish-black markings on the heads and eyes. Adults of the northern masked chafer have conspicuous hair on the thorax and wing covers. The southern masked chafer has sparse hair. The adults are 1/2 inch (11 to 14 mm) long by 1/4 inch (6 to 7 mm) wide. Males have an enlarged fifth tarsal segment on the forelegs that is used to grasp the female. In C. lurida males, the antennal club is shorter or equal to the combined length of the other antennal segments. C. borealis males have a longer club.

Masked chafer larva	Masked chafer raster pattern

Life Cycle and Habits

The northern and southern masked chafers have very similar life histories and habits. Adult beetles usually begin emergence in mid-June and are active into mid-July. Males come to the soil surface after dark before females emerge. The southern masked chafer is apparently active earlier in the evening than its sibling species, the northern masked chafer. Southern masked chafer males begin to emerge just before sunset and skim the ground surface in search of unmated females. Northern masked chafer maximum activity occurs around midnight. Unmated females come to the soil surface, climb upon a grass blade and begin releasing a sex pheromone that attracts the males. Many males often cluster around calling females and the successful male clasps the female with his modified legs during copulation. Mated females and males fly at night and are strongly attracted to lights. The males tend to fly within two feet of the ground while females seem to fly at higher altitudes. Most of the mating and flying activity of the southern masked chafer is finished by midnight. Northern masked chafers are active until a few hours before sunrise. Neither males nor females feed on plant material but merely mate and disperse at night. Mated females dig down four to six inches and lay 11 to 14 eggs. If soil moistures are sufficient, the eggs swell within eight days and hatch in 14 to 18 days at 70 to 75°F. The young larvae burrow to the soil surface in search of plant roots. The larvae also eat general organic material in the soil as well as thatch. The larvae grow rapidly when adequate moisture and food are present. The second instars are reached in 20 to 24 days at 80°F and third instars are common by September. It's during this time of the season that most of the damage occurs. As the soil temperatures begin to drop in the fall, the larvae begin to dig downwards to hibernate. Larvae may dig down 12 inches but most are within three to six inches, at least in southern states. Grubs surviving the winter return to the soil surface in late April and May to feed. The larvae again move down slightly in late May and early June to pupate. A mature larva ready to pupate voids all residue from the gut and the abdomen becomes very translucent. The pupa is formed within the old exoskeleton that splits down the center line. The pupa takes about 17 days to mature.

Northern masked chafer life cycle

Control Strategies

Option 1: Cultural Control—Environmental Modification. Since the eggs require moisture for development, restricting irrigation in July and early August may significantly reduce survival. Since the adults are attracted to lights at night and damage is common under street lights, replace the lights with sodium vapor or yellow lights to reduce their attractiveness.

Option 2: Biological Control—Diseases. Masked chafer larvae can be infected by their specific strain of Paenibacillus popilliae (Dutky) which is called the bacterial milky disease of white grubs. This disease occurs naturally across Ohio, but it usually infects less than 20–25% of a population. There is a commercial product that uses the Japanese beetle strain of this disease. This strain has no effect on the masked chafers so application of milky disease products is not recommended. There are also formulations of the insect-killing white fungus, Beauveria bassiana and the insect-killing green fungi, Metarhizium spp. that are occasionally used to try to control white grubs. Experimental trials using these fungi have yielded poor results in Ohio conditions.

Option 3: Biological Control—Insect Parasitic Nematodes. There are several species of insect parasitic (entomopathogenic) nematodes that are commercially available. Virtually all these nematodes can kill white grubs in the laboratory, but only a few seem to be effective in the field. Species of Steinernema are more effective against cutworms and billbugs, while species of Heterorhabditis are more adept at locating and infecting white grubs. The key to getting successful control is to purchase freshly produced nematodes, applying them immediately and watering them in thoroughly after the application. The treatment area also needs to be kept moist by daily irrigation for three to four days if rainfall is not occurring. Purchase of nematodes should be done with considerable preplanning. Contact potential vendors and describe that you wish to use the nematodes against white grubs in turf. Most suppliers will need a month to prepare fresh nematodes for use. Applications are most successful when the nematodes are used to target late first and second instar grubs (usually in August).

Option 4: Biobased Control—Microbial Products. One of the most promising microbial toxins is based on Bacillus thuringiensis (Bt) strain galleriae. This product has produced 70% control and better when applied against late first and second instar white grubs. The grubs have to ingest the toxin for mortality to occur, so heavy irrigation should be used after spraying or spreading this bacterial toxin. Chromobacterium subtsugae strain PRAA4-1T has also been developed for use on turfgrass. It has also been shown to cause white grub mortality. Again, apply when the grubs are small and irrigate heavily after the application.

Option 5: Chemical Controls—Standard Insecticides, Preventive Treatments. Most modern insecticides used to control white grubs have residual activity within the soil-thatch interface where white grubs feed. This residual activity can range from a couple of weeks to several months, depending on the insecticide. The primary target of these insecticides should be the first instar grub that hatches from the egg to take its first bite of organic matter in the soil-thatch interface. For masked chafers in Ohio, this is usually from mid-July into early August. Most of the neonicotinoid insecticides (i.e., clothianidin, imidacloprid and thiamethoxam) have four to eight weeks of effective residual activity which means that they can be applied in June and July to control the new grubs that arrive in late July and early August. The antranilic diamides (i.e., chlorantraniliprole) seem to have 12 to 16 weeks of effective residual action. This means that applications in April into early August would be effective.

Option 6: Chemical Controls—Standard Insecticides, Curative Treatments. Curative treatments merely means applications made after the grubs have emerged and are actively feeding. The idea is to treat the grubs while they are still small, before they have caused any obvious damage. Products containing carbaryl or trichlorfon can be used in this manner, but carbaryl is heavily adsorbed by thick thatch layers. The neonicotinoids (i.e., clothianidin, dinotefuran, imidacloprid or thiamethoxam) are also useful at this time if watered in after the application. The insect growth regulator, halofenozide, is also useful at this time.

Option 7: Chemical Controls—Standard Insecticides, Rescue Treatments. Rescue treatments are applied when grubs are in the third instar and significant turf damage is occurring or animals are digging the area. To be most effective, these insecticides need to be ingested, which means that the grubs still must be feeding. Grubs that have turned a fat-yellow color are likely not feeding. Products containing clothianidin, dinotefuran or trichlorfon are most useful at this time. If the grubs are suspected to have stopped feeding, only trichlorfon has some contact toxicity. In all cases, the soil and thatch should be moist (may require pre-irrigation) and the application needs to be irrigated immediately after the application. Irrigation amounts of 3/8 to 1/2 inch are strongly recommended, but avoid surface runoff.

This fact sheet is a revision of HYG-2505.