Biosystematics Of The Cotesia Flavipes Complex (hym: Braconidae), Parasitoids Of Gramineous Stemborers
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.