Diapause in the European corn borer, Pyrausta nubilalis (Hübn.)

1. The European corn borer, Ostrinia nubilalis, has a faculative diapause in the last larval instar. Diapause induced in the laboratory by a short-day photoperiod is identical in its intensity to that occurring in the field.2. Diapause development occurs at 30° C. under various photoperiodic conditions but is greatly accelerated by a long day.3. Completion of diapause development does not require a period of chilling.4. Diapause development is a process that removes a block to secretion of the activation hormone but does not include secretion or any of the morphogenic events that follow.

Photoperiodic termination of diapause in an insect

During the last-larval instar, Ostrinia may display a facultative larval diapause. Diapausing larvae contain very low ecdysteroid titers and exhibit poorly differentiated imaginal wing discs. After diapause, development resumes when larvae are placed in favorable post-diapause conditions. After a few days in these conditions, a small and transient peak of 20-hydroxyecdysone was observed in hemolymph before any visible resumption of imaginal wing disc development. [3H]Cholesterol-labeling experiment confirmed this result. Conversion of [3H]Cholesterol into [3H]ecdysteroids also began before any visible resumption of wing disc development. These data suggest that the resumption of wing disc development is induced by very low concentrations of molting hormone. After this small first peak, ecdysteroid concentrations increase until a second peak, which precedes ecdysis. Increase of titers was correlated with an increase of biosynthetic activity from [3H]cholesterol. Unexpectedly, biosynthetic activity remained very high after the second peak, but the synthesized ecdysone was immediately inactivated into 20-hydroxyecdysonic acid.

20-hydroxyecdysone triggers the resumption of imaginal wing disc development after diapause in the European corn borer, Ostrinia nubilalis

Stridulatory structures of the flight wings and elytra, and a dorsal chamber in the thoracic abdominal junction of C. traquebarica Herbst are described. The functions of these structures are considered. A list is provided of 62 species of tiger beetles and 13 species of ground beetles which have stridulatory files on the flight wings.

Sound producing structures in adult cicindela tranquebarica (coleoptera: cicindelidae) including a list of tiger beetles and ground beetles with flight wing files

Commercial resorcin-fuchsin as a stain for elastic fibers.

THE following account shows how to obtain much-improved sections of large heavily sclerotized whole insects. The method should be applicable to many other kinds of animals which present similar problems. Use is made of a fixing, dehydrating, and clearing agent, tetrahydrofuran, which produces a minimum of tissue hardening. It is highly volatile thus permitting rapid removal in the paraffin oven, dissolves paraffin and celloidin. Tetrahydrofuran (furan) has been used by other workers with good results1,2,3. Paraffin infiltration is done in a partial vacuum. The blocks may be soaked 24 hr. or longer in either ‘Mollifex’ (B.D.H.) or in water (preferably with a small amount of detergent) or in 75 per cent alcohol. Before sectioning, the blocks in the soaking medium, if such is used, are cooled to approximately 15°C. Better than average sections are obtained.

Sectioning Large Heavily Sclerotized Whole Insects

THE European corn borer was first found in Ontario in 19201 and, until recently, was primarily a single-generation species, producing one larval brood each summer and overwintering in diapause in the final larval instar. Beginning about 1941, a marked change in the seasonal history of the corn borer occurred. The numbers of larvae completing development without diapause and giving rise to second-generation larvae increased until it now constitutes a substantial part of the total borer population2. As one approach to an understanding of this divergence in seasonal history, we initiated a study on factors in diapause in the corn borer, including environment.

Importance of Photoperiod and Temperature in inducing Diapause in the European Corn Borer, Pyrausta nubilalis (Hbn.)

THE corpora allata are among the endocrine organs in insects controlling larval development1. These organs are also active in the adult stage, exerting effects on metabolism and in some insects on the reproductive organs2.

W. E. Beckel

Papers

Sectioning Large Heavily Sclerotized Whole Insects

Importance of Photoperiod and Temperature in inducing Diapause in the European Corn Borer, Pyrausta nubilalis (Hbn.)

Secretory Activity in the Corpora Allata of Worker Honey-bees (Apis mellifera L.)