The natural history of the neotropical sand wasp Rubrica nasuta (Christ 1791) (Hymenoptera Sphecidae) in Brazil

Abstract

The natural history of the sand wasp Rubrica nasuta (Christ 1791) was
studied at the campus of the Universidade Federal de Minas Gerais, Belo Horizonte,
state of Minas Gerais, Brazil. This is the first comprehensive study of this
neotropical species. The biology of R. nasuta is compared with what is known
about the three other species of Rubrica (J. Parker 1929). Females of R. nasuta
excavate one-celled nests around 10 cm deep in sandy soils in multispecies
aggregations of solitary digger wasps and bees in open areas, like dirt roads.
Nesting activities occur in the rainy season from September to April. Females
typically dig their nests in the morning. One female in 1992 required 2 hr and 28
min to excavate and complete her nest. During nest closure, she smoothed out
the loose soil around the tunnel entrance, effectively disguising it. Provisioning
is progressive and takes no longer than 10 days for a single larva (typically
around 8 days) with some variation based on weather and prey availability. We
estimated about 50 fly prey, especially Syrphidae and Stratiomydae, were required
for one larva. From the 3rd day on, it is common in the morning to see a
female open her nest, re-enter and exit the nest with uneaten pieces or even an
entire prey item held in her mandibles, the so-called discharging behavior. During
the dry season, with temperature around 9 °C, individual wasps will spend
the night in mixed sleeping aggregations on grass inflorescences. Adults were
seen taking nectar on plants with tiny flowers. Males patrol nesting sites and
exhibit territorial behavior. When digging and provisioning, the females are
always very alert against invaders, especially ants. Despite this vigilance, parasitism
by a bombyliid fly is very common. Inquilinous miltogrammine flies emerged
from R. nasuta nests. This is an interesting finding because members of Miltogramminae
are commonly reported as nest parasites of solitary wasps.
KEY WORDS: Rubrica nasuta, behavior, parasitism, nest architecture, natural history.