Acorn preference by the dung beetle, Thorectes lusitanicus, under laboratory and field conditions

Abstract

Processes of seed predation and dispersal are crucial for tree regeneration and forest dynamics. To understand the role of the dung beetle, Thorectes lusitanicus (Col., Scarabaeoidea, Geotrupidae) as secondary seed disperser in Mediterranean oak forests, its food preference was investigated in the field and in the laboratory. This paper had for objectives (1) to explore the feeding preferences for acorns of the two species available in the field: Quercus suber and Quercus canariensis, and (2) to study the olfactory and palatability response of T. lusitanicus to different food resources (oak acorns and dung) under laboratory conditions. The number of beetles in the field was curvilinearly related to the number of acorns, being higher when the number of acorns was intermediate. The maximum values of T. lusitanicus density corresponded to those plots located under Q. suber trees with the highest total weight of acorns. Bioassays with a four-armed olfactometer showed that T. lusitanicus was clearly attracted to volatiles of Q. suber acorns more than to of dung. Palatability bioassays also showed significant preferences for acorns of Q. suber in comparison with the typical food previously described for this beetle species (dung). According to our results, we suggest that a diet based on acorns (due to their high content of polyunsaturated fatty acids) probably satisfies the nutritional requirements of T. lusitanicus during winter, larval development, and metamorphosis.