Scanning electron microscopy of hyposoter didymator (Hymenoptera: Ichneumonidae) in host Mythimna umbrigera (Lepidoptera: Noctuidae) larvae

Abstract

Hyposoter didymator (Thunberg) is an ichneumonid solitary and nonparalyzing parasitoid of noctuids of agricultural importance, native to many Spanish regions, that develops internally in the host until the last instar exits to pupate in a silken cocoon. Larvae of one of its hosts, Mythimna umbrigera (Saalmiller), were parasitized by this ichneumonid, and the morphology of eggs and larvae of the wasp were examined under the scanning electron microscope. The current study revealed that this ichneumonid had a typically hymenopteriform egg with smooth chorion and 3 larval instars with a clear heteromorphosis. The 1st instar was of a caudate type with a caudal appendage as long as 1/3rd of the total body length, weakly defined triangular head, and suctorial mouthparts with no visible mandibles. The 2nd instar was a transition stage with a reduced tail-like caudal segment, a semispheric head that was partially embedded in the thoracic segments, and suctorial mouthparts with conic-shape inner mandibles. The 3th and last instar was typically hymenopteriform, with 13 dorsoventrally compacted segments, vestigial cauda, and inner mandibles. After the larva exited from the host, antennae were not present, but 2 roundish stemmata, production of silk, and papillae-like structures covering the integument with a regular disposition were discernible. Encapsulation of parasitoid eggs was also observed and described at different time intervals after parasitization.