| dc.description.abstract | The species of the Cotesia f/avipes complex are gregarious
endoparasitoids of lepidopteran stemborers of gramineous plants. The complex
consists of three morphologically similar species: C. flavipes, in the Indo-
Australian Region, C. sesamiae in sub-saharan Africa, and C. chilonis in Japan
and China.
The systematics of the Cotesia flavipes complex were studied using:
morphology, morphometrics, cuticular components pattern analysis, allozyme
electrophoresis, Random Amplified Polymorphic DNA-Polymerase Chain
Reaction, mating behaviour, reciprocal crossing and volatile pheromones.
The external morphological characters examined showed a high degree
of intraspecific variation, particularly in colour, density of setae and surface
sculpture. A survey of five morphological characters; scored from sixteen
populations indicated that a combination of the following characters: the
number of hairs on the scutellum, the scuto-scuteller sulcus and the rugosity
on the propodeum could be used to separate the fem~!es and males in the
complex. The shape of the male genitalia was valid 'for separating the
populations of C. flavipes from the other.two species. The male genitalia of the
Mauritius C. flavipes population differed in various aspects from the other
populations of C. flavipes.
Morphometric studies of eleven allopatric populations of the Cotesia
f/avipes species complex were conducted. Sixteen characters were measured.
Canonical Variate analysis separated the complex into three distinct clusters
with populations from Africa clustering together, populations from the Indo-
Australian region and the Neotropics forming a second cluster, and material
from China and Japan forming a third cluster. The Mahalanobis squared
distances between the three clusters were nearly equal.
Cuticular component pattern analysis demonstrated that the pattern of
cuticular components in the three species was not distinct and therefore could
not be used to separate the species. No distinct separations were obtained
using either principal components analysis or canonical variates. The
Mahalanobis distance between the groups indicated that C. flavipes was closer
to C. chilonis than to C. sesemiee. It is suggested that the surface chemistry
of parasitoids may be influenced by their lepidopterous hosts since their fatty
acids serve as precursors ,in the parasitoid hydrocarbon biosynthesis.
Allozyme analysis indicated that esterase, hexokinase, sorbitol
dehydrogenase and 6-phosphogluconic acid det';ydrogenase had fixed alleles for
the three species and could be used to distinguish them. C. chilonis and C.
sesamiae, which have similar male genitalia and partial mating compatibility
are distinct species (Nei's genetic identity, I = 0.587). Average heterozygosity
was very low for all the populations (0.016). Cladistic analysis of the allozyme
data indicated that C. f/avipes may not be a monophyletic group. RAPD-PCR
produced specific banding patterns of the three species and C. glomerata L.
Mating behaviour, volatile pheromones and reciprocal breeding studies
were conducted. Wing fanning and antennal vibration were the initial courtship
signals from the males. Antennal stroking by the male was also an important
contact signal and a prerequisite to successful mounting and copulation.
Interspecific crosses revealed that males of C. flavipes exhibited courtship
behaviour, mounted and copulated with females of C. chilonis and C.
sesamiae, and transferred sperms, but progeny from these crosses did not
include females. Males of C. sesamiae copulated with females of C. chilonis
and the progeny included viable females. The progeny backcrosses of the
hybrid females to male parents also included viable females. Sex pheromone
experiments were conducted in a Y-tube olfactometer and in large field cages.
Males and females of C. f/avipes perceived and responded to odours emitted
by the opposite sex. There was no significant response to odours from
conspecific individuals of the same sex in any or the three species. Pheromone
bioassays in field cages using sticky traps batted with live virgin C. flavipes
females attracted conspecific males.
It is concluded that Cotesia sesamiae and Cotesia chilonis are two
distinct species and can be separated using esterase, hexokinase and sorbitol
dehydrogenase allozym. | en |
