Presence of the exotic dung beetle Euoniticellus intermedius (Reiche) (Coleoptera: Scarabaeidae) in Northern Mexico

Euoniticellus intermedius was first noted on the La Michilia Biosphere Reserve on July 13 of 1992 when two specimens were collected beneath a recently deposited dung pat in forest. Later, in August, six more individuals were collected from 25 dung pats, also in forest. In October, however, an average of one individual per dung pat was collected from 18 natural dung pats in a forest area, and an average of six individuals per pat was obtained from 19 dung pats in a pasture zone, supporting Blume's (1984. Environ. Entomol. 13:1064-1068) contention that the species prefers open areas. In August 1992, at 1800 h in the afternoon, we placed one-liter bovine dung pats at two sites in the Mapimi reserve. Forty dung pats were exposed for 12 hours (1800-0600 h), another forty for 24 hours (1800-1800 h). After exposure, each dung pat was removed and the number and sex of beetles that had buried below the pats as well as those in the dung mass itself were recorded. Euoniticellus intermedius exhibited diurnal activity, colonizing only the pats exposed 24 hours (x = 2.39), confirming Blume's (1984. Environ. Entomol. 13:1064-1068) observation that the species has a narrow range of activity during the day (1400-1700 h). Another exotic dung beetle, Digitonthophagus gazella (F.) sensu Zunino (1981. Fauna Saudi Arab. 3:408-417), was also found to colonize these dung pats. The crepuscular activity of this species allowed it to colonize both 12 hour (x = 2.36) and 24 hour (x = 1.82) exposed dung pats. Both exotic species showed a similar sex ratio with nearly four females to one male. The two species also exhibited variation in nesting behavior at Mapimi similar to that described in the Sahel region of Africa (Rougon and Rougon. 1983. Bull. Soc. Entomol. Fr. 88(7-8):496-513). No other Scarabaeinae were found, though at least two dung rollers, Canthon (Boreocanthon) praticola LeConte and C. imitator Brown, occur in Mapimi. Euoniticellus intermedius also occurs at the La Michilia reserve, but D. gazella has not been found there. Apparently the diurnal activity of E. intermedius facilitates co-existence with D. gazella in the Mapimi reserve.