Beetles Can’t Read Calendars

Members of the Phyllophaga genus are found throughout Florida and most of North America.  One of them is the May/June beetle.  Adults are most active during the rainy season.  So in parts of the country where the wetter months are May or June, the common name of this insect makes common sense.  But, when an area experiences extra rain earlier in the spring, the May/June beetle may emerge from the ground in March or April.  That is what has happened in the western Panhandle this spring.  May/June beetles have been leaving the soil and flying to the lights of people’s homes.

The life cycle of these beetles varies from one to four years.  Eggs are laid in soil each spring by females.  In 3 to 4 weeks, small grubs (larvae) hatch from eggs and develop through three stages (instars), with the first two stages lasting about 3 weeks. The larvae will move closer to the surface and back deeper in the soil as the soil temperature changes.   While close to the surface, larvae feed on grass roots about one inch below the soil surface.  Damaged grass turns brown and increases in size over time.  Heavy infested turf feels spongy and moves when walked upon. The last larval stage remains in the soil from the fall through spring.  The cool soil temperatures drive the larvae deeper in the soil where they remain relatively inactive.  Typically, on the third year, white grubs pupate 3 to 6 inches deep in the soil and emerge as adults.

Larvae, called grubs, vary in length from ¾ to 1 ¾ inches depending on the stages.  Grubs are white with a C-shaped body with a brown head and three pairs of legs near the head.  Adults have ½ to 1 inch long, shiny bodies that are dark yellow to brownish-red in color. Adults do feed on the foliage of several species of ornamental plants, but the damage is typically only aesthetic; not causing long-term harm.

Monitoring of and managing emerging adults can help with deciding on the need for insecticide control for the grubs.  To catch and remove adult beetles, place white buckets containing soapy water near plants that have chew marks or areas with lights at night.  Leave it overnight.  The beetles can easily be disposed of the next day.  If there are more than 12 in the bucket be prepared to monitor the lawn for grubs.  Extra rain or frequent irrigation during the adult flight time may attract more egg-laying females.

To inspect for grubs, turn over sod to a depth of at least two-inches.  If there are an average of three or more per square foot, an insecticide treatment may be needed. To confirm that they are May/June beetles inspect the darkened rear of the grub.  Locate the anal slit.  It should be Y-shaped with two rows of parallel bristles that point toward each other.  This is referred to as the raster pattern.  All grub species can be identified using their unique “butt” features.

The most effective time to control this pest is summer or early fall when the larvae are small.  Remove as much thatch as possible before applying an insecticide.  Spot treat the off-colored area plus the surrounding 10 feet with products containing imidacloprid or halofenozide in early summer.  Follow up in the fall with insecticides such as trichlorfon, bifenthrin or carbaryl if grubs persist.