Friday, August 1, 2014

A Burying Beetle That Doesn't Bury?

 Nicrophorus pustulatus - Photo by Kevin Firth
Our annual All About Mothing event with the Butterfly House volunteers yielded more than moths.  Above is one of several Nicrophorus pustulatus specimens which we found, photographed by Kevin Firth.  It is a burying beetle in the same genus as Nicrophorus orbicollis and the endangered American burying beetle,  Nicrophorus americana that we discussed in previous blogs.  The Nicrophorus species have in common the burying of bird and small mammal carcasses where they deposit their eggs.  Their young subsequently will feed on these carcasses.  The process is described at length in Wikipedia.

Nicrophorus species are somewhat unique among insects (excepting ants and bees) in that the female continues to care for her young as they grow in their carrion-laden burrow, much like mammals protect their young.  Although the young are perfectly capable of feeding themselves, Nicrophorus adults will sometimes feed the young when they beg.  This is a drain on their energy requiring them to increase their food intake and fatten up before egg laying.

N. pustulatus has the largest egg clutches of the Nicrophorus species with up to 200 eggs.  The species has been noted to parasitize the broods of N. orbicollis by laying its eggs on their buried carrion and N. orbicollis may even care for the intruder's larvae.  N. orbicollis has never been observed to parasitize N. pustulatus carrion. 

Unlike most Nicrophorus species, N. pustulatus commonly uses black rat snake eggs.*  A study in 2007 demonstrated that N. pustulatus uses snake eggs as well as carcasses to host their eggs.  Ordinarily a male encountering a mouse carcass will have an elevated sex pheromone emission while a female will have a elevated sex pheromone emission and will oviposit (lay eggs) rapidly.  Their study showed the same response when the beetles are exposed to snake eggs and their larvae can utilize either source or both simultaneously.  The snake eggs are used where they are found and are not moved or further buried like a mouse carcass.  There is debate among experts about how often it utilizes carrion versus rat snake eggs.  In fact, there has been no evidence that this "burying beetle" even buries carrion in its natural habitat! *

Note small orange mites on N. pustulatus's body
The mites seen as small orange dots on the beetle's body above are important in its survival.  The adults carry them and when eggs are laid the mites eat fly eggs and small maggots that otherwise would compete for the carrion food source.  This is a "mite-y" important relationship.

* Here is an interesting article on the relationship of N. pustulatus and black rat snakes.  They may use other snake species and even turtle eggs in the laboratory, an association not yet observed in the field.

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