SAP (PICNIC) BEETLES: Carpophilus spp., including CORN SAP BEETLE, C. dimidiatus, Nitidulidae

ADULT: Many species of these beetles are found in Florida corn.  In general, they are 1/8 to 1/4 in. long, oval-shaped beetles with very short wing covers (elytra) that leave the last half of the abdomen exposed. The last segments of their antennae form a flattened club.  Adults range from tanish brown to black with various patterns of creme to light brown on the elytra and abdomen, depending on species.

EGG: Narrow,  less than 1/16 in. long, white eggs deposited in ears or decaying vegetation. Larvae emerge from eggs in 2 to 3 d.

LARVA: Pale yellow larvae grow to 5/16 in. long. They can be distinguished from legless silk fly larvae by the presence of three pairs of small true legs, a light brown head and the presence of opposing, external mouthparts. Larvae also have intricate, hardened projections from the end of their abdomens that are species specific. Larvae feed within kernels from 9 to 14 d.  They leave ears during the last instar and wander about before entering the soil to construct a pupation chamber.  This prepupal stage lasts 3 to 4 d.

PUPA: They pupate in soil within tightly compacted earthen cells.  Adults emerge in 7 to 9 d.

GENERATION TIME: 21 to 30 d.

DAMAGE: Adults may be found in pre-tassel stage corn, but begin to enter fields in larger numbers as soon as pollen from tassels starts to collect in the whorls and leaf axils. They are attracted to decaying sugarcane stalks and can be very common for the entire season in corn planted to fields freshly rotated from sugarcane.  Larvae can complete development at base of tassel or in leaf axils where shed pollen and anthers collect.  They are also attracted to milk stage kernels. Tight husk tips help to prevent access to ears with undamaged husks. Bird or any insect damage to husks predisposes ears to attack.  Fermentation products attract beetles to the damaged ears where several hundred adults of several species may quickly congregate.  Beetles then move to attack other ears in the field. Physiological stress to plants that results in ears growing out of the tips of the husks can also result in sap beetle damage. Adults deposit eggs soon after their arrival in the ears. Larvae and adults completely hollow out kernels. Adults introduce bacterial and fungal pathogens (including Aspergillus) that grow in the damaged kernels.

CONTROL: Several families of predacious beetles feed on sap beetle larvae within infested corn ears, but this obviously occurs after the ears become unmarketable. Varieties with tight tips and plenty of tip cover provide fairly good protection to Florida corn.  A good armyworm and earworm control program that maintains the integrity of the corn husks usually keeps these beetles from damaging the crop, especially in sweet corn.  Birds should be kept away from maturing corn fields as much as possible to reduce the husk and kernel damage that leads to subsequent sap beetle infestation and damage.  In areas prone to sap beetle damage, consideration should be given to spatially or temporally separating fields to reduce situations where a field is at harvest when neighboring fields are silking. Pesticides are available as foliar applications to control adult sap (picnic) beetles. Formulations, rates, and pre-harvest intervals of insecticides for sap (picnic) beetle control are listed below for sweet corn (Table 1) and field corn (Table 2).