Host shift by the burying beetle, Nicrophorus pustulatus, a parasitoid of snake eggs

Recent work [Ecoscience (2000) vol. 7, 395-397] suggests that the burying beetle Nicrophorus pustulatus may have undergone a remarkable host shift, exploiting snake eggs rather than carrion as resources for breeding. We conducted behavioural and physiological experiments to examine the hypothesis of a host shift and to formulate hypotheses on its origin. Two congeners of N. pustulatus, Nicrophorus orbicollis and Nicrophorus defodiens did not respond to snake eggs with typical breeding behaviour. When N. pustulatus male-female pairs (n = 14) were presented with clutches of snake eggs, the number of offspring but not the mean size of offspring varied with snake egg mass, indicating effective regulation of brood size. When breeding on turtle eggs, N. pustulatus had a more variable response than when exploiting snake eggs, suggesting that turtle eggs are not a primary resource for breeding. Nicrophorus pustulatus presented with both snake eggs and a mouse carcass combined and exploited the two resources within the same nest (10 of 12 trials). Mouse carcasses and snake eggs were treated differently. Carcasses were moved, buried and stripped of hair in a manner characteristic of burying beetles, whereas snake eggs were not moved or buried. Females that discovered a mouse carcass also had a significantly greater juvenile hormone increase than did females discovering snake eggs. Some responses to the two resources, however, were similar. Female N. pustulatus oviposited rapidly in response to either a mouse carcass or snake eggs, and males elevated sex pheromone emission in response to either resource. The efficient use of snake eggs, the ability to regulate brood size and the different responses to snake eggs and carrion suggest that N. pustulatus is well adapted to exploiting snake eggs for breeding. The use of snake eggs by N. pustulatus has potential implications for conservation of oviparous reptiles.