Sexual
selection has given rise to the
evolution of unique and bizarre
structures and behavioural traits. Male
beetles of the coleopteran family
Malachiidae are endowed with remarkable
chitinous structures that are associated
with complex glands (= exciter organ).
The elaboration and location of these
organs vary considerably among the
Malachiidae. We hypothesised that these
exciter organs play a role during
courtship and might provide females
either with valuable substances and/or
with a signal of male quality. In M.
bipustulatus the exciter organ is
located on the forehead. Its structure
allows females to insert their
mouthparts in a fashion that looks like
the female would bite into the male's
head. Field observation of a total of
123 courtship interactions of this
species revealed that interactions
lasted 31 ± 36min (range: 1-160min, n =
92). During courtship the female
repeatedly bit into the exciter organ.
The mean duration of single bites was 25
± 17s (range: 2-26s, n = 25). The total
duration of female contact with the male
exciter organ was 28 ± 28min (range:
1-100 min, n = 26). In some cases the
occurrence of droplets at the exciter
organ or female's mouthparts suggested
that actually some substance was
transferred from the male to the female.
After each biting the female turned
around and the male touched the female's
abdomen tip with its mouthparts. In 85
out of 123 cases the female left without
copulation; only 10 interactions
resulted in a final copulation (mean
duration: 26 ± 9s, range: 17-39s, n =
9). In 21 cases, other males
aggressively interfered with courting
pairs and seemingly tried to take-over
the females. Six M. bipustulatus
males were found in the field feeding on
other males (preferably on the head).
Even direct attacks and killing of
paired and unpaired males was observed
in four cases. This was surprising since
malachiids are actually pollen feeders.
Our observations suggest that males
offer valuable secretions during
courtship to the female. Males try to
attain these secretions even by killing
and feeding on congenders. Whether
female choice is based on qualitative or
quantitative aspects of the secretion is
not yet known.
Index
terms: Malachiidae, courtship
feeding, female choice, male
competition, cannibalism
Copyright:
The copyrights of this original work
belong to the authors (see
right-most box in title table). This
abstract appeared in Session 4 –
CHEMICAL AND PHYSIOLOGICAL ECOLOGY
Symposium and Poster Session,
ABSTRACT BOOK I – XXI-International
Congress of Entomology, Brazil,
August 20-26, 2000.