Imaginai Moult Research Articles

Ultrastructural organization of the seminal vesicles of Baculum thaii (Phasmida, Phasmatidae) during sexual maturity

A morphological and ultrastructural study was carried out on the seminal vesicles of Baculum thaii removed from individuals killed at 4, 10 and 20 days from the imaginai moult, with the intention of showing any modifications that these structures undergo during sexual maturity. From the comparative examination, clear evidence was found of epithelial transformations of these organs during sexual maturity: there was a gradual increase in cellular volume accompanied by a progressive development of the apparatus of synthesis. The most particular characteristics, however, in the individuals killed at 10 and 20 days from the moult were, in addition to a marked secretory activity, the presence of spermiophagic activity, which had never been found in the genital tracts of this order of insects. In the light of these results, it can be affirmed that the seminal vesicles of B. thaii, apart from being the site of the secretory activity necessary for maintaining the sperm in this area, also assume an important role in the processes of “controlling” and “regulating” sexual material that is kept ready for transfer to the female genitalia.

Analysis of postembryonic development of locomotor activity rhythm by corpora allata implantation in the cricket gryllus bimaculatus

1. 1. Male crickets Gryllus bimaculatus show a drastic change in circadian rhythm from nymphal diurnality to adult nocturnality, in association with an increase in activity level several days after the imaginai moult. 2. 2. The corpora allata implantation into male 7th or 8th instar nymphs produced supernumerary instar nymphs in about 30% of the implanted animals, but did not affected the normal development in the remaining animals. 3. 3. The majority of the supernumerary instar nymphs were diurnal and sexually inactive, although their internal reproductive organs appeared to be fully mature. 4. 4. The supernumerary instar nymphs became nocturnal with an increase in activity level several days after the imaginai (9th) moult. 5. 5. The roles of the nervous system in the regulation of the rhythm reversal are discussed.

Developmental changes in ecdysteroid biosynthesisin vitroduring adult life and embryogenesis in a cricket,Giyllus bimaculatusde Geer

Summary Ovaries from female adults of Gryllus bimaculatus produce considerable amounts of free and conjugated ecdysteroids in vitro. The rate of ecdysteroid synthesis after a 16 h incubation in Grace's medium, changes during vitellogenesis in a characteristic way, reaching a peak value of about 5 ng per hour, per animal, at days 4/5 after ecdysis, when animals start to deposit eggs. During incubation of pieces of the female abdominal integument together with the adjacent segmental fat body, a net synthesis of moulting hormones is observed, similar to that in the ovary. Ecdysteroid production by integument starts shortly after the imaginai moult and also reaches a maximum of about 3 ng per hour, per animal, around days 4/5 after ecdysis. Both tissues mainly synthesize and release ecdysone into the incubation medium. From tissues of male adult crickets only the abdominal integument shows a significant net synthesis of ecdysteroids. In vitro incubations of egg homogenates of various ages result in a net synthesis of free and conjugated ecdysteroids in older embryos, with a maximum one day before hatching of the larva. The imidazole compound KK-42 does not inhibit ecdysteroid synthesis in vitro in cricket embryos.

Evolution of the cuticular pigmentation as a system for developmental timing for Panstrongylus megistus and Rhodnius prolixus adults

A system for developmental timing for Panstrongylus megistus and Rhodnius prolixus (Hemiptera: Reduviidae) adults is presented, using as a marker, the evolution of the cuticular tanning after ecdysis. In both species the setting of the cuticular pigmentation pattern after imaginai moult is a homogeneous process in population, i.e. no individual variations were detected. The system allows one to estimate the exuvial time up to 5 or 7 hr after occurrence. A preferential exuvial period (PEP) was determined in the population under usual rearing conditions by using this system. The PEP runs from 2100 to 0500 hr for P. megistus and from 0100 to 0800 hr for R. prolixus. These data are meaningful for endocrine studies on those species. Studies on PEP under natural environmental conditions would be useful for the control of Chagas’ disease vectors.

Biology and behavior ofEctomocoris xaviereiVennison & Ambrose 1990 (Heteroptera Reduviidae Piratinae)

Ectomocoris xavierei Vennison & Ambrose 1990, a polymorphic assassin bug lays dull white, elongately oval eggs 12.67 ± 0.61 days after imaginai moult. Eggs are laid singly and each litter consists of 7.66 ± 0.76 eggs. E. xavierei deposits its eggs in the soil and takes 2 to 4 min to deposit an egg and a maximum of 12 eggs are deposited in a day. The eggs hatch in between 23 to 27 days and pinkish red nymphs turn black with yellow markings within 45 to 60 min. The total nymphal period from hatching to imaginai moult is 93.6 days. Description of nymphal instars and a key for the identification of nymphal instars are given. Females live longer than the males and a females biased sex ratio is recorded. It preys in the following sequential pattern: arousal — approach — pouncing — rostral probing — stylets penetration — prey transportation and feeding. The sequence observed in the mating behaviour is: arousal — approach — embracing — genitalia extension and connection — copulation — post copulatory act.

Oogenesis in immature stages and sterile castes ofKalotermes flavicollis(Fabr.) (Isoptera Kalotermitidae)

Ovaries of winged and dewinged imagos, 2nd instar nymphs, pseudergates, presoldiers and soldiers of Kalotermes flavicollis were investigated. During the normal developmental cycle, after the imaginai moult, the ovary starts to produce eggs as a result of the activation of oogenic processes. In pseudergates, presoldiers and soldiers oogenesis is blocked at the first previtellogenic stage and the oocytes undergo degeneration. In nymphs a block is also observed, but it happens at the second previtellogenic stage and without any hint of oocyte degeneration. The evidence suggests that in pseudergates, presoldiers and soldiers, the oogenesis block is related to a lack of differentiation of follicular cells which may be one of the main targets for control factors.

Spatial distribution of the cockroach, Blattella germanica, in a swimming‐bath facility

AbstractA population of Blattella germanica L. was studied in a swimming‐bath facility using a sampling method. A set of traps deposited weekly, over a period of 50 weeks, allowed us to follow the variations of the temporal and spatial distributions of the population inside the building. A Factorial Correspondance Analysis, performed on the data, led us to the conclusion that the population was stable in time. The spatial distribution of the insects was contiguous. Inside an aggregate, we were able to define a circular movement from the center towards the periphery and vice versa; this movement can be superimposed up on the biological development on the individuals. After birth in the middle of the aggregate, during development, larvae explore further a field as far as the border of the aggregate; this exploratory phase, related to foraging behavior or search for new shelters when these become limiting factors, could be considered as the spreading phase of the population. Then, with the imminence of the imaginai moult, old larvae tend to gather in high density areas in the middle of the aggregate. Newly molted adults look for a sexual partner. And finally females remain in the shelters during oothecae maturation.RÉSUMÉDistribution spatiale d'une population de Blattella germanica L. dans une piscineL'étude d'une population de Blattella germanica L. dans une piscine par des piégeages hebdomadaires pendant une période de 50 semaines, nous a permis de suivre l'évolution spatiale et temporelle de cette population. Les résultats des piégeages étudiés par Analyse Factorielle des Correspondances nous permettent de conclure à une certaine stabilité temporelle de la population. Elle se répartit en larges agrégats dans lesquels s'inscrit un mouvement circulaire, allant du centre vers la périphérie et retour, qui se superpose au cycle de développement des individus.

Developmental time and mortality of larvae of Triatoma infestans infected with Trypanosoma cruzi

Triatoma infestans were infected with Trypanosoma cruzi (zymodeme 1) at the first feed after eclosion from the egg; interstadial development times and mortality rates were then recorded until the imaginai moult and compared with those of uninfected controls. No retardation of development occurred in infected bugs and their mean total mortality rate (9%) was only slightly higher than that (6%) of uninfected controls (due solely to 4 additional deaths). This is the first demonstration, under optimal and standardized rearing conditions, that infection of T. infestans with T. cruzi has little or no effect on development times or mortality rates.

Factors influencing male accessory gland activity and first mating in Triatoma infestans and Panstrongylus megistus (Hemiptera: Reduviidae)

Males of the Triatominae, Panstrongylus megistus and Triatoma infestons, show a considerable difference concerning the time necessary for them to acquire the capacity for the first mating. P. megistus copulates from the eighth day of adult life, irrespective of whether or not it has been fed, while T. infestons copulates about 17 days after the imaginai moult and only after a blood-meal. These differences might be due to the secretory activity of T. infestons male accessory glands whose full development is reached only after two saturant blood-meals. If allatectomy is performed in male P. megistus soon after the imaginai moult, accumulation of secretion does not occur in 3 of the 4 accessory glands. Topical application of precocene II (200 μg/insect)a few days before or soon after the imaginai moult in P. megistus, halves the amount of secretion in the accessory glands.

Multichemical defense of plant bugHotea gambiae (Westwood) (Heteroptera: Scutelleridae): (E)-2-hexenol from abdominal gland in adults

The occurrence inHotea gambia adults of a sexual dimorphism in the divided dorsal abdominal scent gland (dg 1)is reported. Counts made of ducted secretory units indicate that female dg 1 regresses at the end of larval development, unlike male dg 1 which undergoes no regression. Other dorsal abdominal scent glands (dg 2, dg 3) which function in the larvae cease to function during the imaginai moult. From gas chromatographic, mass spectrometric and [(1)H]NMR data, the identity of the secretion from male adult dg 1 was established as virtually pure (E)-2-hexenol (a 100-mg mature male adult contains 0.5-1 μl of secretion). 2-Hexenol was also found in the reduced female adult dg 1. In the sexually monomorphic metathoracic scent gland, (E)-2-alkenals (C6, C8) and (E)-4-oxohex-2-enal, together with monoterpenes (β-pinene, limonene) but not 2-hexenol, were identified. The vapor of (E)-2-hexenol is repellent to both sexes ofHotea adults and toxic to blowfly (Calliphora) eggs.

Control of corpus allatum activity during the imaginai diapause in females ofLocusta migratoriaL

In the Savio strain of Locusta migratoria an imaginai diapause is induced by long daylength. In diapausing females, the haemolymph level of juvenile hormone (JH) was undetectable during the first 3-wk of imaginai life and later rose only slightly to about 20 ng/JH3IR per ml. Only peripheral cells of the corpora aliata (CA) were active. In nondiapausing animals, or after the termination of diapause, the JH level was high (140–200 ng/ml) and the ultrastructure of the gland exhibited signs of activity. CA severance in 3-wk-old diapausing females terminated diapause as a result of activation of the CA. CA disconnection in the fifth larval instar or at the imaginai moult in long daylength animals did not break diapause and the CA stayed inactive. The lateral cells of the protocerebrum exert a jdual effect: at the end of larval life they bring about CA maturation and render them active, whereas during the imaginai diapause they inhibit CA activity. The median neurosecretory cells of the pars intercerebralis sup...

Functional development of the auditory system of the cricket,Teleogryllus commodus

1. InTeleogryllus commodus andT. oceanicus, vibration of the tibia of the prothoracic leg at audio-frequencies stimulates auditory receptors in the tympanal organ, despite immobilization of the large tympanum by vaseline. 2. Responses of characteristic auditory interneurons in the adult cervical connective are similar whether stimulation is by sound or by vibration of the tibia (Figs. 3–5). 3. Interneurons in second-last (A-2) and last (A-1) immature instars are stimulated by sound and by vibration of the tibia and we conclude that these interneurons are the same as those recorded in adults (Figs. 6, 7). Peripheral receptors and some interneurons in the immature auditory system are, therefore, physiologically competent. 4. At the imaginai moult, auditory threshold at the optimum frequency decreases dramatically (Fig. 8 A). This increase in sensitivity to sound is attributed mainly to the appearance of the auditory tympanum in the adult. There is a much smaller increase in sensitivity to vibration of the tibia at audio frequencies between last instar nymphs and adults (Fig. 8 B). 5. From the A-2 to adult stages ofT. commodus, auditory receptors stimulated by sound show a peak sensitivity at 3.8 to 4.0 kHz (Fig. 8 A). Such tuning must be independent of vibration characteristics of the tympanum and of acoustic resonance characteristics depending on the dimensions of the leg trachea.

Effect of different lighting conditions on circadian developmental rhythms and behaviour inEphestia kuehniellaZell

Abstract A study was made on the developmental rhythms of Ephestia kuehniella during different photoperiods: constant lighting (L/L), under conditions of 12 hours light per day (L/D) and in constant darkness (D/D). Observations were made every 2 hrs, for 3 successive 24‐hr periods, of the number of wandering larvae emerging from food, the number of pupations and of imaginai moults. Emergence of wandering larvae is rhythmic only under L/D conditions, and in addition this is also affected by the density of the larvae. Rhythm is least apparent with greatest density of the larvae. Pupation in E. kuehniella is a non‐rhythmic process with each of the photoperiods examined, whereas the imaginai moult is characterized by an endogenous (existing under D/D conditions) rhythm. Emergence of imagines is non‐rhythmic under L/L, and also when pupae under L/D fail to receive the final period of darkness. The rhythm of the imaginai moult is possibly controlled by the biological clock, which stops under conditions of constant light.

Caenis cuniana sp. n., a Parthenogenetic Mayfly

Caenis cuniana n. sp. is described. Females, soon after the imaginai moult, are ready for oviposition. The number of eggs laid varied usually between 100 and 300. The time required for hatching var...