Relative warp analysis to study morphological variations in the genital capsule of Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae)

Abstract

The influence of the host on the morphology of the male genital capsule of Trichogramma pretiosum Riley was studied by geometric morphometric analysis. Specimens of the parasitoid obtained from 10 different Lepidoptera host species were used. Initially, landmarks were defined and Cartesian coordinates (x and y) for each landmark of the genital capsule of all specimens were obtained. The anatomic landmarks transformed to Cartesian coordinates were then analyzed by generalized orthogonal least-square procedure. Consensus configuration of the genital capsule for all specimens was obtained and partial and relative warps were determined. Fifteen landmarks generated 24 relative warps for each specimen. The ordination of the relative warps (alpha = 0), using shape components, separated T. pretiosum into four different hosts groups: (1 - Alabama argillacea (Hueb.), Helicoverpa zea (Bod.) and Diatraea saccharalis (Fabr.); 2 - Danaus plexippus erippus (Cramer), Hamadryas feronia (Linn.) and Spodoptera frugiperda (J.E. Smith); 3 - Anticarsia gemmatalis Hueb., Bonagota cranaodes Meirick and Diaphania sp. and 4 - Anagasta kuehniella (Zeller). The two first axes of the relative warps explained 83.0% of the total variation of the genital capsule shape of the specimens. The main difference was at the anterior region of the posterior extension of the dorsal lamina of the genital capsule. Although results obtained were initial and exploratory they have demonstrated that subtle shape differences in the male genital capsule can be detected by geometric morphometric analysis.