Giovanni Sbrenna

The embryonic apolyses of Schistocerca gregaria (Orthoptera)

The origin and differentiation of the ecdysial glands and the appearance of the cuticles were studied in embryos of Schistocerca gregaria at corresponding stages. The development of the cuticle was also studied in headless embryos explanted in vitro. The ecdysial glands originate in the early stages before blastokinesis from two symmetrical invaginations of the ectoderm between maxillae I and II. The buds grow and enlarge forming a bilayered cellular sheet. The changes occurring in the gland and in nuclear volumes as well as its histological structure are evidence of a cyclic glandular activity in the embryos. An embryonic cuticle is formed in later stages after blastokinesis: before hatching an apolysis occurs and a new cuticle, a larval cuticle, is formed with which embryos hatch. The embryonic apolysis seems to be correlated with the cycle of the ecdysial glands. However, embryonic abdomens, severed from the head long before the ecdysial gland shows any signs of activity, develop when explanted in vitro as do whole embryos in vitro and in ovo. Like normal embryos these headless embryos form two cuticles. Hence, embryonic apolysis appears not to be under the control of the embryonic ecdysial gland.

Behavioural differences between male and female replacement reproductives in Kalotermes flavicollis (Isoptera, Kalotermitidae)

Summary: An ethogram type study was performed on representative colonies of Kalotermes flavicollis to investigate the behavioural repertoires of replacement king and queen. Our observations suggested a sex-based behavioural specialisation in the two reproductives, affecting colony organisation and equilibrium. Interesting differences were detected in overall activity of the two reproductives, with the male showing the greatest frequency of movements in the nest, vibratory acts, and the highest rate and range of social contacts. In addition to his importance for periodical insemination of the queen, the king might also play a basic role in the social structure and dynamic development of the colony, as a “mediator” in social interactions between the queen and the other colony members.

A morphological and ultrastructural study of Telosentis exiguus (Acanthocephala, Palaeacanthocephala)

Abstract Scanning electron microscope observations on Telosentis exiguus (Acanthocephala), an endoparasite of Atherina boyeri (Osteichthyes, Atherinidae), provided more detailed and precise data on surface structures of taxonomic relevance. Trasmission electron microscope observations on the integument revealed the presence of numerous channels which penetrate the integumental syncytium and, through branching, increase (up to 61 times) the absorptive surface area. Bundles of filaments and an electrondense cytoplasmic matrix in the outermost region provide a cytoskeletal support.

Role of the juvenile hormone on the differentiation of specialized integumental areas, “fenestrae”, in Schistocerca gregaria (Acrididae: Orthoptera)

Abstract “Fenestrae” or “Slifers patches” are highly permeable integumentary areas of locusts, segmentally arranged in the adult abdominal terga of males and females. In S. gregaria they arise, after being newly programmed, from epidermal cells, and the developmental pattern proceeds during the last two larval instars. In order to study the mechanism by which the cells that form these areas respond to the hormonal stimulus to change commitment, 4th- and 5th-instar larvae were surgically allatectomized or treated with precocene. When performed within the first 24 h of the 4th-instar, allatectomy, whether surgical or chemical, leads to the appearance of precocious adults, with the integumentary areas on all terga. If removal of the corpora allata is done after that period, the precocious adults have smaller integumentary areas, and if the removal is delayed for 48 h, differentiation of the areas does not occur at all in the last terga. Topical application of juvenile hormone to the sites of the presumptive areas of the 4th-instar larvae, allatectomized during the first 12 h, reduces the specialized differentiation. The presence or absence of juvenile hormone commits the integumentary-area-forming cells to the deposition of larval or specialized cuticle, respectively. The hormonal events during the larval instars and an asynchronism of the integumentary cellular cycle may explain the distribution of these integumentary areas.