During field studies in Kentucky in 1994, this beetle was observed laying egg clusters on "Golden Queen" sweet corn. When the researchers returned to observe the larvae they found instead that the eggs had been eaten before they had time to hatch. So they attached some egg clusters from a laboratory colony of the twelvespotted lady beetle to sweet corn stalks and leaves, then observed the egg clusters at timed intervals to find out who was eating them. Over a 24-hour period, 95% of the the egg clusters placed on the sweet corn were attacked. Direct observations of predators feeding on the eggs revealed that the primary source of predation was actually egg cannibalism by twelvespotted lady beetle adults and larvae! Only two other individuals (a multicolored Asian lady beetle larva and a spined soldier bug nymph) were seen feeding on the twelvespotted lady beetle eggs.
During this study it was discovered that the twelvespotted lady beetles in the sweet corn field also laid their eggs on a weed species, hophornbeam copperleaf (Acalypha ostryaefolia). Although other weeds such as pigweed, lambsquarters and prickly sida were present, egg clusters were only found on sweet corn and hophornbeam copperleaf. Egg clusters placed on hophornbeam copperleaf suffered much less cannibalism over a twenty-four hour period than did egg clusters placed on sweet corn. It is possible that hophornbeam copperleaf, and potentially other weeds or crops, may provide an alternative site for the twelvespotted lady beetle to lay eggs. This alternative egg laying site may protect the eggs from being cannibalized by other twelvespotted lady beetles.
- T. E. Cottrell, R. S. Pfannenstiel, and K. V. Yeargan, University of Kentucky