Glenn L. Holbrook

Reproductive biology of the German cockroach, Blattella germanica: Juvenile hormone as a pleiotropic master regulator

Juvenile hormone (JH) exerts major pleiotropic effects on cockroach development and reproduction. The production of JH by the corpora allata (CA) in the adult female German cockroach, Blattella germanica, is dependent upon and modulated by both internal and environmental stimuli. Mating, intake of highquality food, social interactions, and the presence of vitellogenic ovaries facilitate JH synthesis. Conversely, starvation, deficient diets, enforced virginity, isolation, and a pre- or post-vitellogenic ovary cause the CA to produce less JH. Sensory stimulation of the genital vestibulum by the ootheca also inhibits the CA via signals that ascend the ventral nerve cord. All these stimulatory and inhibitory signals are integrated by the brain, and a preponderance of favorable signals results in a graded lifting of brain inhibition, permitting the synthesis and release of JH. The effects of inhibitory signals on JH biosynthesis can be lifted experimentally by severing nervous connections between the brain and the CA. Such an operation accelerates activation of the CA. Besides controlling gonadal maturation in females, JH concurrently regulates the production of sexual signals, including both attractant- and courtship-eliciting pheromones, and the behavioral expression of calling (pheromone release) and sexual receptivity. Although JH is required for the expression of copulatory readiness in female B. germanica, it appears that signals associated with copulation (spermatophore, sperm, accessory secretions) can inhibit this behavioral state even when titers of JH are permissive for receptivity. These observations suggest that JH might regulate sexual receptivity in females indirectly through

Endocrine regulation of de novo aggregation pheromone biosynthesis in the pine engraver, Ips pini (Say) (Coleoptera: Scolytidae)

Abstract In vivo and in vitro radiotracer studies were conducted with the pine engraver, Ips pini (Say) (Coleoptera: Scolytidae), to elucidate the relationships among feeding on host ( Pinus jeffreyi Grev. & Balf.) phloem, juvenile hormone III (JH III) biosynthesis, and de novo aggregation pheromone (ipsdienol) biosynthesis. The in vivo incorporation of [1- 14 C]acetate into ipsdienol by male I. pini increased with increasing dose of topically-applied JH III, demonstrating the stimulatory role by JH III in de novo pheromone production. In vivo incorporation of ( RS )-[2- 14 C]mevalonolactone into ipsdienol by male I. pini was not affected by increasing JH III dose. However, injection of [ 14 C]mevalonolactone resulted in significantly higher levels of [ 14 C]ipsdienol than those observed in saline-injected controls. This is direct evidence for the mevalonate-based isoprenoid pathway in de novo ipsdienol biosynthesis, and suggests that in this pathway JH III does not influence enzymatically-catalyzed reactions subsequent to the conversion of 3-hydroxy-3-methylglutaryl-coenzyme A to mevalonate. An additional in vivo [ 14 C]acetate study demonstrated that de novo ipsdienol biosynthesis is also stimulated by feeding on host phloem. Lastly, an in vitro radiotracer study utilizing L-[ methyl - 3 H]methionine demonstrated that feeding stimulates JH III biosynthesis by the corpora allata (CA) of male, but not female, I. pini . Analysis by radio-high pressure liquid chromatography revealed that JH III is likely the type of juvenile hormone produced by the male CA. These data support a sequence of events leading to feeding-induced de novo pheromone biosynthesis in male I. pini : (1) feeding on host phloem; (2) feeding-dependent JH III biosynthesis by the CA; and (3) JH III-stimulated de novo ipsdienol biosynthesis.

Role of feeding in the reproductive 'group effect' in females of the German cockroach Blattella germanica (L.)

We have found that whether a female German cockroach, Blattella germanica (L.), is kept alone or in the presence of another female has a major impact on how fast it reproduces and how much it eats. By the sixth day of adulthood, females paired since adult eclosion had substantially larger oöcytes than did females isolated during the same time, and females paired with intact females, or with ones rendered incapable of feeding, consumed more rat chow in the first six days of adulthood than did isolated females. The stimulatory effect of pairing on reproduction was, however, partially independent of feeding because the oöcytes of solitary and paired females differed in size on day 6 even when they were given, and had consumed, the same amount of food. This result was confirmed with analysis of covariance using the total food intake of a female as the covariate in the analysis. A females social condition probably influenced the development of its oöcytes by affecting the quantity of juvenile hormone synthesized by its corpora allata. The corpora allata of paired females produced more hormone than did those of isolated ones, even when all females had consumed an equivalent amount of food. Moreover, females treated with a juvenile hormone analog, fenoxycarb, reproduced more quickly than identically reared and fed control females, showing that juvenile hormone could influence reproduction independently of feeding. We conclude that both group rearing and food intake accelerate oöcyte development by diminishing the brains inhibition on the synthesis of juvenile hormone.

An adaptive benefit of facultative coprophagy in the German cockroach Blattella germanica

1. A possible adaptive benefit of coprophagy was investigated in nymphs of the German cockroach Blattella germanica (L.).

Improved conditions for culture of biosynthetically active cockroach corpora allata

SummaryCurrently, short-term culture of insect corpora allata is most often performed in TC199. We now show that L-15B, a medium widely used in arthropod tissue culture, is superior to TC199 for both short- and long-term culture of cockroach corpora allata. In 3-h and 48-h incubations, juvenile hormone biosynthesis by corpora allata from Diploptera punctata was significantly higher in L-15B than in TC199. In addition, in both media, corpora allata activity was significantly improved by flotation of glands at the medium surface. Characteristics of L-15B responsible for its superiority were examined by comparison of gland activities in several TC199 formulations that had been modified in different ways to be more similar to L-15B. Adjusting the osmotic pressure of TC199 (288 mOsm/l) to near that of L-15B (362 mOsm/l) and D. punctata hemolymph (360 mOsm/l) significantly improved gland activity during the second 12 h of a 36-h incubation. Increasing the concentrations of amino acids, sugars, and organic acids in TC199 to the same levels as in L-15B significantly improved gland activity during both the second and third 12-h intervals of a 36-h incubation. These results suggest that L-15B is superior to TC199 because L-15B is isoosmotic with D. punctata hemolymph and because L-15B, like cockroach hemolymph, contains a high level of organic constituents. It is therefore more appropriate to use L-15B than TC199 for short-term in vitro assays of juvenile hormone biosynthesis and for extended corpora allata culture.

Control of Cell Proliferation in the Corpora Allata During the Reproductive Cycle of the Cockroach Diploptera punctata

Unlike in Blettelta gcrmanica and Supella longipalpa, the corpora allata (CAI of Diploptera punctafa exhibited cyclic changes in cell number during the reproductive cycle. In mated females, a wave of DNA synthesis followed by mitosis resulted in a significant increase in CA cell number from about 9,000 cells on day 0 to 12,000 cells at ovulation on day 8. Subsequently, the number of cells per CA underwent a gradual decline to about 10,000 cells by day 64. During this long period of gestation, mitotic activity was undetectable (by colchicine arrest) and pycnotic nuclei were frequently observed by transmission electron microscopy. Just before parturition on day 72 another mitotic wave was detected and CA cell number increased again. The early wave of CA cell proliferation could be postponed by delaying mating or abolished by maintaining females as virgins. Neural disconnection of the CA from the brain mimicked the effect of mating, suggesting that enhanced cell proliferation is permitted by the removal of inhibitory signals from cerebral neurosecretory cells. The proliferative activities after mating were neither abolished by ovariectomy, which suppressed the normal increase in JH synthesis, nor elevated by unilateral allatectomy, which doubled the rates of JH synthesis in the remaining CA. These data corroborate previous results (Szibbo and Tobe, 1981 a; Tobe et al., 1984; Johnson et at., 1993) and suggest that waves of cell proliferation and JH synthesis, though simultaneous, are regulated independently by inhibitory signals from cerebral neurosecretory cells. D 1996 Witey-Liss, Inc.

Social influences on nymphal development in the cockroach, Diploptera punctata

Solitary male nymphs of the cockroach Diploptera punctata (Eschscholtz) (Blattaria: Blaberidae) took significantly longer to reach adulthood than males paired with either a male or female nymph or grouped with four other male nymphs since birth. When isolated throughout nymphal development, 15.8% of males passed through 3 stadia before adult eclosion, and the remainder went through 4 stadia. In contrast, 61.3% of paired males became adults in 3 stadia. Males need not, however, be isolated or paired for the entire nymphal period to express isolated or paired patterns of development. About 60% of males paired in just the first stadium or its initial 9 days became adults in 3 stadia, and only 20.4% of males isolated in the first stadium and the first 3 days of the second reached adulthood within 3 stadia. Although the first stadium was a critical period in which social condition determined the course of future development, analyses of covariance showed that isolated males gained less weight than paired ones, not only in the first stadium, but in the second as well. Moreover, the degree of growth of a male in the second stadium, measured as either weight gain or relative growth rate, did not depend on the male’s social condition in the first stadium, because isolated second‐instar males grew less than paired ones, even when both sets of insects had been paired in the first stadium. Female nymphal development, unlike that of males, was not greatly affected by social factors.

Neural control of cell size in the corpora allata during the reproductive cycle of the cockroach Diploptera punctata (Dictyoptera: Blaberidae)

Summary Rising and subsequent falling rates of juvenile hormone (JH) synthesis occurred concurrently with synchronous growth and atrophy of CA cells during the ovarian cycle in mated adult females of Diploptera punctata. Ultrastructural observations revealed that growth of CA cells resulted from synchronous proliferation of cellular machinery required for JH synthesis. Cell growth was suppressed in CA of virgin females, in which rates of JH synthesis remained low, but was stimulated by mating or by severance of nerves leading from the brain to the CA. Atrophy of CA cells during declining rates of JH synthesis was due to synchronous autophagy of cellular organelles. While the mechanism initiating autophagy is unclear, it is independent of nervous connections between the CA and brain. We propose that under normal physiological conditions the quantity of JH synthesized by a corpus allatum is determined largely by the total amount of cellular machinery available for JH production. Therefore, the cycle of JH s...

Juvenile hormone synthesis in relation to corpus allatum development in embryos of the viviparous cockroach Diploptera punctata

Summary Few studies have addressed endocrinology of the corpora allata (CA) in insect embryos. We now report on development and biosynthetic activity of CA in embryos of a viviparous cockroach, Diploptera punctata. When newly-eclosed adult females of D. punctata were mated, they oviposited and gave birth, respectively, about 8 and 73 days later; thus, gestation and corresponding embryogenesis lasted approximately 65 days. Dorsal closure, which coincides with differentiation of the CA, was concluded when embryos were about 13 days old and had completed 20% of embryogenesis. Reverse phase-high performance liquid chromatography revealed that embryonic CA released predominantly juvenile hormone III (JH) in vitro. Furthermore, an in vitro radiochemical assay showed that between day 28 of embryogenesis (43% of embryonic development completed) and hatch rates of JH synthesis rose, plateaued and then fell. When CA activity was increasing or was high, from day 28 to 54 (83% development), mitosis occurred at low an...

Development‐activity relationships in nymphal corpora allata of the cockroach, Diploptera punctata

Abstract. In females of Diploptera punctata the corpora allata undergo a gradual increase in volume during most of the second nymphal stadium. In the first half of the stadium, steady growth of the glands results from a progressive increase in the size of constituent cells. Late in the stadium, cell size declines but the volume of the glands continues to rise due to an increase in cell number. Changes in cell size during the stadium displayed a distinct pattern in relation to Juvenile Hormone (JH) synthesis. Both cell size and activity increased during the first two‐thirds of the stadium, peaked early in the last third of the stadium, and decreased before the moult. The rise in cell numbers late in the stadium corresponded to a wave of cellular mitosis and occurred after a steep decline in the rate of JH biosynthesis. Exposure of late second instars to fenoxycarb. a JH analogue, depressed mitosis significantly, suggesting autocrine regulation of cell proliferation in the corpora allata. Possible mechanisms modulating sequential cycles of growth and atrophy of cells and cell proliferation in these glands are discussed in relation to temporal patterns of JH and ecdysteroid titres in nymphs.