Reproductive isolation and circadian release of sex pheromones in Euxoa (Lepidoptera: Noctuidae).
Creators: name: Teal, Peter E. A.
Publisher: name: Université d'Ottawa / University of Ottawa
Year: 1978
Subjects: subject: Biology, Entomology.

description: The nocturnal calling behavior of three closely related, interfertile species of cutworm moths, Euxoa declarata, E. campestris, and E. rockburnei, was studied in the laboratory at four different temperatures. The temporal pattern of calling activity by virgin females was found to differ for each species, with peak periods of pheromone release by each species remaining distinct at each of the experimental temperatures. The calling period of declarata was found to be exclusive from that rockburnei and nearly exclusive from that of campestris at. all temperatures. An overlap between the calling periods of campestris and rockburnei was found to occur, however the initial and peak phases, which under natural conditions with males present, would be by far the most important, were found to be separated by a minimum of 2 hours. Decrease in dark phase temperature was found to cause a shift to earlier calling by females of all three species, however such shifts did not eliminate the differences in the peak periods of release of pheromones occurring among the three species. Although differences in the periods of pheromone release may not be the only mechanism involved in the reproductive isolation of the species belonging to the declarata group, differences in the calling periods are sufficient to account for the strong conspecific mating tendency exhibited by these species in laboratory tests and are certainly major components of reproductive isolation. The calling period of E. declarata (female) X E. rockburnei (male)(F1) hybrid females was found to correspond almost exactly with that of the maternal declarata stock. The calling period of the reciprocal cross was found to be extended, intersecting the calling periods of both parental species, however, the major activity peak occurred early in the scotophase. The female terminalia, including abdominal segments 8 and 9 + 10 of Euxoa were found to be similar to the typical type of terminalia described for higher Lepidoptera by Mutuura (1972) and have evolved to enable the females to oviposit in the soil. Structural modifications adapted for pre-oviposition digging include: the heavily sclerotized 8th tergite, anterior position of the copulatory opening on the 8th segment, the reduced 8th sternite, the elongate and highly flexible cuticle of the 8th intersegmental membrane, the heavily sclerotized dorsal valves, the eversible ovipositor, and extensive musculature throughout the ovipositor. The functional aspects of these features in oviposition are discussed and a description of the mechanics of oviposition extension, digging and retraction is given. Epidermal gland cells of the ovipositor were found in two specialized areas. One area is located in the ventral intersegmental membrane between segments 8 and 9 + 10. The "Class I" epidermal gland cells of this area were found to undergo progressive vacuolation for several days after adult emergence and comprise the sex pheranone gland. Glandular cells were also found to occur on the dorsal and lateral surfaces of the dorsal valves. These gland cells are typical trichogenous cells communicating with tubular setae. The function of large "droplets" within these cells and their presumed secretion is unknown at present.