Segregation of temporal and spatial distribution between kleptoparasites and parasitoids of the eusocial sweat bee, Lasioglossum malachurum (Hymenoptera: Halictidae, Mutillidae)

Abstract

Cuckoo bees and velvet ants use different resources of their shared host bees, the former laying eggs on the host pollen stores and the latter on immature stages. We studied the activity patterns of the cuckoo bee Sphecodes monilicornis and the velvet ant Myrmilla capitata at two nesting sites of their host, the social digger bee Lasioglossum malachurum, over a 3 year period. Due to the difference in host exploitation, we expected different temporal patterns of the two natural enemies as well as a positive spatial association with host nest density for both species. At a daily level, S. monilicornis was more abundant between 10.00 and 15.00 h, while M. capitata was most active in the early morning and late afternoon; both species activities were independent from host provisioning activity. The activity of cuckoo bees was in general positively correlated with the density of open host nests (but not with the total number of nests), while that of velvet ants was rarely correlated with this factor. Sphecodes monilicornis was seen both attacking the guard bees and directly entering into the host nests or digging close to nest entrances, while M. capitata only gained access to host nests through digging. We conclude that the temporal and spatial segregation between the two species may be, at least partially, explained both by the different resources exploited and by the different dynamics of host interactions.

Scramble competition by males of the velvet ant Nemka viduata (Hymenoptera: Mutillidae)

“…Competition is high not only because a male-biased sex-ratio, but also from the relatively narrow daily temporal window in which males and females are active (early morning and late afternoon), a pattern typical of mutillid wasps irrespective of the temperatures at the reproductive sites (from the hot summers of Michigan, Minnesota and southern Spain sand dune systems to the cool spring of central Italy) (Chapman et al, 1926;Evans, 1982;Polidori et al, 2009aPolidori et al, , 2010aPolidori et al, , 2012. In addition to an inverse relationship with temperature previously reported for N. viduata female activity (Polidori et al, 2010a) (and, thus, likely occurring also for males, given the very similar daily distribution), the activity of the host species was also negatively associated with that of the parasitoid (Polidori et al, 2010a).…”

“…Data of activity and body mass were transformed as ln(x + 1), while number of host nests, number of plots and number of sites were transformed as x 1/2 . Parametric least-squares regressions were used to evaluate the distribution of activity during the day, testing whether the simplest regression model (linear or quadratic) fitted the data distributions (see, for example, Polidori et al, 2009aPolidori et al, , 2010a. A multiple linear regression based on the data from the PT method was performed to look for a significant effect of female activity, number of host nests and plots' identity on the activity of males (transformed values).…”

“…This pattern is especially likely in aggregations from which many mutillid females may emerge from host nests over the course of the flight season (Polidori et al, 2009a(Polidori et al, , 2010a. Some observers have suggested that either males or females of some species may stridulate to attract mates (Manley, 1977;Bayliss & Brothers, 1996) but other than laboratory studies of copulatory behaviour (e.g., Bayliss & Brothers, 2001;Bergamaschi et al, 2010), many details of the mating systems of mutillids remain unknown.…”

“…Wingless female mutillids search for nests of their hosts, which may be solitary or social species, ground-nesting or wood-nesting. Females usually enter nests when hosts are absent (in the early morning or late afternoon) in order to deposit eggs on the mature larvae or prepupae of their host species (Brothers et al, 2000;Polidori et al, 2009aPolidori et al, , 2010a. If discovered near or within a nest, female mutillids may be attacked by the nest owner (Polidori et al, 2009a) but are well protected by their thick cuticle, powerful sting and other adaptations (Schmidt & Blum, 1977).…”

“…Most researchers have focused on the taxonomy of the group (Schmidt, 2006) or on the hosts parasitized by mutillids, largely other aculeate hymenopterans (Brothers et al, 2000;Polidori et al, 2009aPolidori et al, , 2010a. Wingless female mutillids search for nests of their hosts, which may be solitary or social species, ground-nesting or wood-nesting.…”