Parental Care in the Subsocial Intertidal Beetle, Bledius Spectabilis, in Relation To Parasitism By the Ichneumonid Wasp, Barycnemis Blediator

Abstract

The parasitic wasp Barycnemis blediator (Aubert) is an important natural enemy of the subsocial saltmarsh beetle Bledius spectabilis Kratz: the wasp occurs at high densities (up to 100 coccoons m -2 ), it is very widely distributed among the beetle colonies, and life-table analysis shows that up to 15 % of the immature stages can be killed by the wasp. To determine whether the mother beetle can protect her young against parasitism, we recorded in the field the reactions of individual wasps to burrows that contained either a single adult beetle, an adult and young (the larvae leave the maternal burrow about halfway through the 1st instar) or individual 1st, 2nd or 3rd instars. The wasps only went down those burrows that contained a single, post-dispersal Bledius larva, except once in 132 observations when a wasp was observed to go down a maternal burrow containing a female, eggs and larvae. On all other occasions, burrows containing adult Bledius were not entered by the wasp. None of the five hundred 1 st instar larvae collected from maternal burrows in the field was parasitized. This was not because 1st instars in maternal burrows are unattractive or unsuitable for the wasp: field experiments showed that the wasps were highly successful in parasitizing 1st instar larvae taken from maternal burrows and placed in experimental burrows. Field experiments showed that the success rate of parasitism by the wasp was much higher with 1 st instars (94 % ) than with 2nd (69%) or 3rd (35%) instars. We suggest that an important consequence of parental care in Bledius spectabilis is that the young are protected from attack by the parasitic wasp Barycnemis blediator for most of their most vulnerable phase (the 1st instar).