Hemolymph Juvenile Hormone Titers Research Articles

Ovaries and regulation of juvenile hormone titer in Acheta domesticus L. (Orthoptera)

A study was performed on females Acheta domesticus to examine the effects of various experimental conditions on the ovarian physiology. Using a radioimmunoassay to determine juvenile hormone (JH) titers as well as in vitro JH biosynthesis, we observed that retention of mature follicles in egg-retaining females, i.e., virgins or mated females not provided an egg-laying substrate, inhibits JH production and consequently oocyte development. Mating in intact as well as ovariectomized females does not affect corpora allata activity. It is only when mating is associated with egg laying that JH biosynthesis and hemolymph titers increased and oocyte development and fecundity are stimulated. Despite lower JH biosynthesis, ovariectomized females present enlarged corpora allata and the levels of JH observed in their hemolymph were intermediate between those of intact egg-laying and virgin females. In intact females, the hemolymph JH titers as well as the JH esterase activities were related to ovarian development. JH esterase activity was very high in ovariectomized animals. Several factors involved in ovarian development of A. domesticus are discussed.

Hemolymph juvenile hormone titers and growth of terminal oocytes throughout the first gonadotrophic cycle inAiolopus thalassinus

In Aiolopus thalassinus (Fabr.) (Ins.: Orth. :Acrididae) juvenile hormone III OH-Il l ) , is the only homologue detected in the hemolymph [4]. It stimulates synthesis and secretion of vitellogenin in the fat body. This precursor of egg yolk protein is then sequestered and deposited as vitellin by the developing oocytes. All terminal oocytes grow synchronously into eggs. The corpora allata (CA) are the sites of JH synthesis; allatectomy prevents the production of JH in locusts and in grasshoppers, no eggs were formed [1]. Treatment of A. thalassinus females with precocene-III (an antihormone) inhibits the secretion of JH-III , and induces sterility in adult females [4]. In female acridids, CA size and JH hemolymph content increase during the first gonadotrophic cycle [2]; CA activity and reproduction are well correlated, but the CA volume is not always a valid indication for reproductive activity. The biosynthetic activity of the glands is suggested as a good indicator. However, there can be large individual variations in relation to the age of the adult females. Using the GC-MS-MIS technique, Rembold and Lackner [7] quantified the JH contents of different insect length and width of the terminal oocytes were measured; the volume of the terminal oocytes was checked throughout the whole cycle. Table 1 demonstrates a modulation of the JH-I I I hemolymph pool during the first gonadotrophic cycle of A. thalassinus which is very similar to that of L. migratoria as reported by Rembold [6].

Temporal variations of hemolymph esterase activity and juvenile hormone titers during ovocyte maturation in Acheta domesticus (Orthoptera)

Using in vitro methods, juvenile hormone (JH) esterase activity and α-naphthylacetate esterase activity were determined in the hemolymph during the first reproductive cycle of the house cricket, Acheta domesticus. Biochemical properties of the hemolymph JH esterase were studied. α-Naphthylacetate esterases increased during the first gonotrophic cycle:peaks of their activity could be observed concomitant with peaks of JH esterase activity. The fluctuations in JH esterase activity correlated with those of hemolymph JH titers. The results are discussed.

Critical period of sensitivity to juvenile hormone for the invagination of tracheoblasts into the developing flight muscle fibers of Locusta migratoria

The effect of juvenile hormone (JH) on the process of tracheolization of the dorsolongitudinal flight muscles of the migratory locust is studied during larval flight muscle development. The ratio of the number of interfibrillar tracheoles in a muscle fiber to the total area of this muscle fiber is used as a parameter for quantitative assessment of the invagination of tracheoblasts into the muscle fibers. Elevation of the hemolymph JH titer following implantation of active corpora allata (CA) during the period of Day 5 of the fourth larval stage up to and including (except in one case) Day 2 of the fifth larval instar results in a complete prevention of the invagination of tracheoblasts into the muscle fibers at the end of the fifth larval stage, whereas implantation of CA on Day 3 and Day 5 of the fifth larval instar results in a partial and decreasing inhibition of the invagination process. The amount of JH III per locust recovered 24 hr after CA implantation on Day 5 of the fifth instar (0.70 ng) is higher than after CA implantation on Day 1 of this instar (0.54 ng), pointing to the absence of a substantial increase in JH-specific esterases. Due to a rise in hemolymph volume, however, JH titer after CA implantation on Day 5 is lower; yet the lowering of the titer is not likely to be responsible for the time-dependent decrease in effect of CA implantation. Rather, because ecdysone titer fluctuates during the last larval instar, it would appear that exogenous JH must be administered before the initial increase in ecdysone titer in order to completely prevent invagination of tracheoblasts into the muscle fibers at the end of the fifth larval instar. It is suggested that JH acts by preventing the development of the tracheoblasts to an ecdysone-receptive state.

Neuroendocrine regulation of corpus allatum activity in Manduca sexta : Sequential neurohormonal and nervous inhibition in the last-instar larva

The inactivation of corpora allata (CA) in the last-instar larva of the tobacco hornworm Manduca sexta was studied using in vivo assay methods that test the capacity of the glands to induce an extra larval molt. Results indicate that the CA are inactivated by a two-step process. In the first step, a neurohormonal inhibition occurs by day 1 after ecdysis, resulting in a decrease in the ability of the glands to respond to allatotropin. The inhibitory hormone appears to be secreted by the medial neurosecretory cells in the brain and remains in the hemolymph only for a short period of <2 days. The second step of inactivation occurs by day 3; it is neurally mediated and essentially terminates juvenile hormone secretion. Neither the neurohormonal nor the neural inhibition is reversible under the conditions used in our larval assays. The timing of the two stages of inhibition coincides with the two periods of reduction in hemolymph juvenile hormone titer; this suggests that the regulation of corpus allatum activity plays an important role in reducing the juvenile hormone titer during the last larval instar-a prerequisite for the transformation of the larva into the pupa.

Hormonal control of migratory flight in Oncopeltus fasciatus: The effects of the corpus cardiacum, corpus allatum, and starvation on migration and reproduction

The effects of starvation on the activity of the corpus allatum (CA) and on migratory flight behavior and as the effect of the corpus cardiacum (CC) on migratory behavior were examined. Juvenile hormone (JH) titer determinations were done on Oncopeltus hemolymph using the Manduca pigmentation bioassay. Starvation resulted in a decrease in measureable JH in Oncopeltus hemolymph over a period of 5–6 days after which time JH titers were undetectable. Flight behavior increased for the first 4–6 days after the beginning of starvation, then decreased to very low levels as JH titers diminished. Topical applications of the JH mimic ZR512 to starved individuals 9 days after starvation restored flight to its former high level. However, implantation of three CC into starved Oncopeltus at this time had no effect on flight. Oviposition was also inhibited by starvation. Feeding Oncopeltus on suboptimal food (green pods) resulted in a significant delay in reproduction and an increase in flight activity similar to that seen in diapausing individuals. Therefore, JH is the primary hormone responsible for the stimulation and coordination of migration and reproduction while the CC appears not to be involved in the stimulation of migratory behavior in this species. Food shortage or suboptimal food appears to be important in initiating the spring migratory flight by maintaining the hemolymph JH titers at a level below the threshold for ovarian development but above that necessary to stimulate migratory flight.