Biology and Pest Management of the
Sunflower Beetle in North Dakota (continued)
E-824 (Revised,) March 2000
Life Cycle
Figure 5. Life cycle of the sunflower beetle. (Click on each image to get a larger version)
| MAY | JUNE | JULY | AUGUST | SEPTEMBER | OCTOBER |
 Adults from previous season
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| Eggs laid in stems |
Larvae feed on upper foliage | Pupation in soil |
Adults of this season |
Adults over- winter in the soil  |
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APRIL 
WINTER
The sunflower beetle has one generation per year in the northern plains. Adults overwinter
in the upper 2 to 4 inches (5-10 cm) of soil and emerge from the previous sunflower fields
in May to early June. Beetles overwinter throughout the field and exhibit no preference
for field edges or shelterbelts. Research indicates that a degree day (DD) model and
calendar dates are equally accurate in predicting the onset and 50 percent emergence of
the sunflower beetle population. The DD model is initiated on March 1st and is based on
soil temperature at a depth of 2 inches (5 cm) and a base of 32oF (0oC).
Sunflower beetles begin to emerge at a mean of 416 DD oF (232 DD oC),
and 50 percent of the adult emergence occurs by 710 DD oF (395 DD oC).
Shortly after emergence the beetles begin to feed, mate and lay single eggs on stems and undersides of leaves. Adults live for about 8� weeks and lay eggs for a 6-7 week period. Each female lays approximately 850 eggs with a range of 200-2,000 eggs. About 14 eggs per day are laid. Egg survival is about 70 percent in the laboratory but is estimated at only 50 percent in the field. Some eggs fail to hatch due to predation, egg sterility, and unfavorable weather conditions like hot, sunny weather. Eggs hatch into larvae in about one week. The larvae have four instars, which feed and are present in fields for about six weeks. When mature, larvae drop to the soil where they pupate in earthen cells. The pupal stage lasts from 10 days to two weeks. A new generation of adults (called the summer generation) emerge in late July through early September and feed for a short period on the uppermost leaves or bracts of sunflower before burrowing back into the soil to overwinter. Feeding by the summer generation adults causes minimal damage to the maturing sunflower plant. These adults do not mate or lay eggs until the following spring.
Hosts
Sunflower beetles are generally restricted to cultivated or wild sunflower and a few close relatives. Adults and larvae are observed on wild sunflower including Helianthus annuus L., H. petiolaris Nuttall, H. nuttallii Torrey and Gray, H. pauciflorus Nuttall, H. maximiliani Schrader, H. tuberosus L., and H. giganteus L. In Texas, they have also been found on woolly leaf bursage, Franseria tomentosa Gray.
Crop Damage
Damage due to adult feeding begins soon after beetles emerge from hibernation. They seldom feed on the cotyledons, but the first true leaves may be severely damaged or completely consumed. If beetles are abundant, fields may be severely defoliated. Adults feed predominately on leaf margins while larvae feed over the entire leaf surface. When larvae are numerous, damaged leaves take on a lacy appearance. Damage may be most noticeable in field margins. Most larval feeding occurs at night, and adults will feed during the day. During the daytime, larvae typically rest in the terminal growth area where they are easily found in leaf and flower buds. If larval feeding is severe, defoliation can reduce yield by poor seed set or fill.
The late summer generation of emerging sunflower beetle adults rarely causes economic damage to the sunflower crop. However, in some cases they have been abundant enough to cause feeding injury on late-planted sunflower.
E-824 (Revised,) March 2000
