Anomiopsoides cavifrons (Burmeister, 1861)

Gillett, Michael P. T. & Gillett, Conrad P. D. T., 2017, New Observations on Three Species of Eucraniine Dung Beetles (Coleoptera: Scarabaeidae: Scarabaeinae) in Mendoza and San Juan Provinces, Argentina, The Coleopterists Bulletin 71 (4), pp. 817-820 : 817-819

Anomiopsoides cavifrons (Burmeister, 1861)

This species was first encountered on the morning of 27 December 2016 in sand dunes south of the town of Caucete (San Juan) at km 550 on RN 20 (31.66°S; 68.21°W, 580 m elevation) ( Fig. 1 ). This site was visited five times over the next few days, and specimens of A. cavifrons were found in abundance during mid-morning (9:00–10:00) along, and on both sides of, at least a half-km stretch of roadside sand dunes and inland for at least 100–150 m. Compared to the beetles’ level of activity during the morning, their activity in the late afternoon (17:00–18:00) was significantly reduced (by an estimated 90–95%). At this time, the sandy ground was extremely hot, and air temperatures in the shade were above 35° C. Altogether, more than 150 specimens were observed. These beetles varied noticeably in size, ranging 7–12 mm in body length, excluding the head, as measured according to Ocampo (2005) .

We observed foraging behavior of A. cavifrons during about five morning hours over the period of 27–29 December 2016. From individual burrows, beetle tracks diverged in all directions. However, their foraging differed significantly from published accounts in that at least 20% of all beetles encountered were carrying dead leaves, flower heads, or seeds of unknown plants into their burrows. At no time were they observed transporting dung, even though dried fecal pellets and horse droppings were readily available. Foraging for dead leaves and plant seeds by this species has been described, but was not at first attributed as the main food source ( Ocampo 2005). However, it was subsequently noted on occasions that foraging of plant matter by A. cavifrons was more marked and that burrows could be stocked almost exclusively with this material ( Ocampo 2009). Our observations seem to confirm this, suggesting that this population shows perhaps a complete dependence upon plant material, at least during late December.

A surprising number of beetles (at least 15%) were encountered with soft exoskeletons, although they were more or less fully pigmented. They were judged to be recently eclosed teneral specimens, and they, too, were actively engaged in transporting plant material. This suggests that mid- to late December may be a peak time for emergence, which would fit in very well with the temporal distribution of this species given by Ocampo (2005) (see below). These teneral specimens were extremely delicate and, if handled, had a tendency to become accidently squashed, releasing a surprisingly large volume of liquid (~50–100 µl). Zunino et al. (1989) postulated that the unusual food relocation and burial behavior undertaken by eucraniines may represent an adaptive evolutionary response to life in arid environments, promoting the subterranean rehydration of the food to render it more satisfactory. It would be very interesting to discover the physiological and biochemical means that allow them to accumulate so much water, given the extremely arid climate where they occur and their diet of plant material. Indeed, it may be possible that new and recently emerged specimens of A. cavifrons feed on the plant material at first to obtain water and then later switch to foraging on dried dung.

Observations of this species in the month of December do not seem to have been recorded before, and in Ocampo’ s (2005) temporal distribution for this species, only two museum specimens are noted as being collected in December, with one other from November. The others are all from January (75% of specimens), with smaller numbers from February and March.

A second population of A. cavifrons was encountered in the late morning of 27 December 2016, near the small community of Marayes (San Juan), just north of the intersection of RN 141 and RP 510 (31.60°S; 67.60°W, 565 m elevation) ( Fig. 2 ). The habitat again consisted of sand dunes and was similar to the Caucete site. Relatively few (six specimens) A. cavifrons were observed here, but again, the only material seen being transported was vegetation, and not dung pellets. A further six sites along the RP 510 were explored over a distance of about 60 km, and no eucraniines were encountered, although burrows characteristic of A. cavifrons were observed at most sites containing sand dunes. It is probable that our timing, in the early afternoon, was too late for finding the beetles active.

Figures

Figs. 1–3. Localities and habitats for Eucraniini in San Juan and Mendoza, Argentina. 1) Habitat of Anomiopsoides cavifrons and Eucranium belenae in sand dunes south of the town of Caucete (San Juan); 2) Habitat of A. cavifrons in sandy area near the small community of Marayes (San Juan); 3) Habitat of Anomiopsoides fedemariai and E. belenae on the sandy riverbank of the R´ıo Mendoza, where it is intersected by RN 142 (Mendoza).