May or June Beetles (annual species)
- Scientific Name: While there are over 150 species of May-June beetles, Phyllophaga spp., known in North America, the southwestern June beetle, P. crinita Burmeister, is especially troublesome in Texas and southern Oklahoma. While this species can be the main grub in a given area, it often occurs mixed with southern and southwestern masked chafers, Cyclocephala lurida and C. pasadenae, as well as another June beetle, P. submucida. [Phylum Arthropoda: Class Insecta: Order Coleoptera: Family Scarabaeidae]
- Common Names: May beetle, June beetle, Junebug, Hanneton, phyllophaga
- Climatic Zone: Subtropical and southern temperate
- Geographic Distribution: Phyllophaga are native to North and Central America and most species in the northern states take three to five years to complete development. P. crinita is an important pest in Texas and Oklahoma but its know range extends to Louisiana and Georgia.
- Damaging Stage: Larvae damage roots of grasses and possibly ornamental plants as they feed on the organic matter (especially thatch) found at the soil-thatch interface of turfgrasses. Adults feed at night on deciduous tree leaves, occasionally causing severe spring defoliation.
- Hosts: All southern and transition zone grasses are attacked, but damage is most common in bermudagrass and St. Augustinegrass.
- Damage Symptoms: Damage is typical for white grubs; damaged turf wilts as if under drought stress and eventually this turf dies in irregular patches. The grubs of P. crinita are about the same size as masked chafers. Damage to bermudagrass can occur from late August through November. When heavy populations occur, the turf turns brown as if not being irrigated and the turf can be lifted like a loose carpet. These grubs may also damage turf from May into June, but most southern turfgrasses outgrow the grub damage at this time.
- Description of Stages:
The life stages of P. crinita are typical of white grubs, and the larvae can generally be identified to genus by looking at the raster pattern. An expert is needed to identify different species of May/June beetle larvae.
Eggs: The white oval eggs are usually about 3/32 inch (2 mm) long and are placed singly in earthen cells. The eggs absorb moisture and become more round.
Larvae: Phyllophaga larvae are very difficult to separate to species and an expert is needed to make a proper identification. However, P. crinita larvae have a broadly U shaped anus and two parallel rows of bristles pointing towards each other on the raster. Full grown grubs are about 7/8 to 1 inch (20 to 25 mm) long. Third instar grubs may be found at any time during the year though most of the population takes one year to complete development.
Pupae: The pupae are white at first and become brownish with age. Most pupae are 5/8 to 7/8 inch (15 to 22 mm) long.
Adults: The adults of P. crinita are a light reddish-tan color and are often confused with masked chafers that can be flying at the same time. P. crinita adults generally do not have a dark spot on either side of the pronotum and the leg claws have a preapical tooth (the tarsal claws each look like they have two teeth). Adults are usually 1/2 to 5/8 inch (12 to 18 mm).
- Life Cycle and Habits:
Studies in Texas have revealed that grubs of P. crinita can be found in the soil in any month of the year. Apparently, if conditions are poor (probably drought), the grubs may take a second year to complete development. Overwintered larvae pupate from mid-May through early July and adults emerge to mate and lay eggs from mid-June to the end of July. However, in drought years, the adults may remain in the soil until rainfall coaxes them out to mate and lay eggs. In these conditions, adults have been known to have heavy flights in late July through mid-August for the few nights following a thunderstorm.
Unlike other Phyllophaga, P. crinita apparently does not feed extensively, if any, on the foliage of deciduous trees and shrubs. As the females emerge, they release a sex pheromone that attracts males for mating. Mated females may fly short distances, but they appear to burrow back into the soil to lay their eggs. Males are attracted to lights and commonly annoy residents when they fly into lighted windows or onto screen doors. Eggs are placed 2 to 3 inches into the soil and must absorb moisture before they develop. After 20 to 30 days, the eggs hatch and the young larvae burrow upwards in search of organic matter, thatch, and plant roots. The larvae develop rapidly in moist soil conditions, or they may remain fairly deep in the soil profile during hot-dry conditions. Third instar larvae are about the only stage present by mid-October. In cooler temperatures, the grubs move downward and remain quiet until soil temperatures begin to rise in the spring.
- Control Approaches:
Cultural Control - Habitat Modification - Since the eggs require moisture for development, restricting irrigation in July and early August may significantly reduce survival. Adult Phyllophaga are attracted to lights at night and damage can be concentrated under or around street lights. Replace the lights with sodium vapor or yellow lights to reduce their attractiveness.
Natural Control - Milky Diseases and Parasites - Milky diseases caused by strains of Bacillus popilliae are known but commercial preparations do not contain Phyllophaga-specific strains. Larvae are also commonly attacked by Tiphia wasps but these wasps may require several seasons to build up populations sufficient to control these pests.
Biological Control - Insect Parasitic Nematodes - The insect parasitic nematode, Steinernema glaseri, was used before 1940 and had considerable promise but this agent was not developed further because of problems of rearing and expense. This nematode may be economically available in the future. Commercially available products containing strains of S. carpocapsae have been marginally effective. Preparations containing Heterorhabditis spp. seem to be the most effective of the currently available nematodes. Nematodes should be applied when white grubs are in the second instar. Irrigation before and after nematode application with 1/4 inch of water minimum increases efficacy.
Chemical Control - Insecticides -
Targeted Treatments: As with most soil-inhabiting insects, insecticides are most effective when small stage grubs are the target. For annual species of Phyllophaga, the small first instar grubs are often present in late June through early August. Applying an insecticides 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 September. These middle instar larvae are also very susceptible to control, but if not controlled, turf damage may begin to appear by late August. From early September to October, the third instar grubs are 40 to 60 times the body weight of the newly hatched, first instars. By this time, significant damage may be caused by skunks, raccoons, armadillos and birds that dig up infested turf to feed on the grubs.
Curative Treatments: Insecticide applications made in late September and October yield poor control of third instar grubs. At this time, insecticides known to have rapid action and are least affected by thatch binding are effective.
In late April and May, masked chafer grubs return to the upper soil level to briefly feed. Though grub damage may be evident at this time, skunk and racoon damage is usually the major problem. If necessary, insecticides with rapid action may be used.
Preventive Treatments: The recent labeling of long residual (>120 days) neonicotinoid and diacylhydrazine insecticides has made it possible to obtain grub control with a single application in May, June, July or August. Depending upon the time of application, some of these new insecticides simultaneously provide control of a broad range of insect pests other than grubs. Unlike carbamate or organophosphate insecticides, these new materials have low impact on beneficial organisms that live in the turf. Both liquid and granular formulations are available. Some require posttreatment irrigation, others do not. Read and follow label instructions for optimum results.
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.
The adults can be monitored using 15 Watt black light traps. Trap counts can be plotted on graph of numbers versus date. When the trap capture has decreased for ten days, mark the date of peak activity. The grubs will be most susceptible to controls about six weeks after this peak. A simple method of monitoring adult occurrence is to suspend a 60 Watt light bulb over a dish or small plastic wading pool. Beetles attracted to the light fall into the water and are easily counted and removed each morning. Grub infestations should be evaluated as early as possible by monitoring, accurate identification and mapping of infested areas. 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.
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 annual species of Phyllophaga larvae is 6 to 8 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 raccoons often find less than six grubs per 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.