Cerceris grandis Banks

Davidson, J. M., 2003, Mexican Acmaeodera Eschscholtz, 1829: A new species and checklist, with miscellaneous taxonomic and biological notes on other North American Buprestidae (Coleoptera), Zootaxa 201, pp. 1-18 : 12

Cerceris grandis Banks ( Hymenoptera : Sphecidae ) predation upon Gyascutus plani­

costa ( LeConte, 1858) ( Buprestidae )

In early July of 1971 north of Blythe, Riverside Co., California, large numbers of Chrysobothris biramosa calida Knull, 1958 and Gyascutus planicosta were observed on leaves and branches of mature Atriplex lentiformis (Torr.) Wats. (Chenopodiaceae) plants. A number of predatory wasps, Cerceris grandis , were observed attacking adult Gyascutus and then flying or dragging them back to their nests. Cerceris grandis is only about onefifth the size of the Gyascutus , but they were successful in stinging the beetles in the prosternal area and injecting venom to paralyze them during most attacks. During the attack, the beetles became noticeably agitated and tried to escape, but they were much less agile than the wasps and would merely drop to a lower branch on the plant only to be rediscovered by the wasps moments later. When the venom took effect, the beetles would usually fall to the ground where the wasps would adjust their position and carry them in a venter to venter, head forward position. The wasps always flapped their wings in a burst of energy, carrying the beetles in an arc of a few meters before the weight of their prey pulled them back to the ground. The wasps would then again adjust their hold on their prey, fly off again only to fall to the ground once more. This process was repeated many times until the Cerceris females reached their ground nests, sometimes as much as 100 meters or more away from the capture site. Occasionally, the wasps would appear to become fatigued and would drag their prey along the ground rather than continue to fly with it. Sometimes the wasps would be successful in stinging their prey while the beetle was on a leaf or stem, the wasp clinging to its prey. In a few cases, when the wasp did not drop the beetle, she would attempt to adjust the beetle while both were on a leaf and then take flight. Usually this was not successful and she would drop the beetle into the plant and not find it again. Cerceris grandis was not observed preying on any specimens of C. biramosa calida on Atriplex plants. The reasons for this are unclear, but it seems that because the Gyascutus are so much larger and less agile than the Chrysobothris , it was simply more efficient to attack and capture larger prey. The C. biramosa calida were much more agile than the G. planicosta and therefore, very likely more difficult to capture.