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

Abstract

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 other directives. In males, JH accelerates not only the onset of sexual readiness but also synthesis of accessory reproductive products.Lastly, we present a novel cockroach control strategy that is based on the intimate association between food intake and rising JH titers in B. germanica females. JH analogs cause abortion of fertile oothecae in gravid females. In turn, rising JH titers and vitellogenic oocytes induce feeding in females. With strategic placement of insecticidal baits and JH analogs, gravid females, which normally feed little and are difficult to control, can thus be effectively targeted for elimination.

Differential physiological responses of the German cockroach to social interactions during the ovarian cycle

“…However, unlike oviparous species, the egg case is then rotated 90° and retained externally by the female, attached at the vestibulum (an outer chamber that lies above the enlarged seventh abdominal sternite), until the nymphs hatch approximately 21-22days later at 27°C (Roth and Stay, 1962). This incubation period is functionally similar to gestation in ovoviviparous cockroaches, as the corpora allata (CA) are inhibited in both groups, suppressing juvenile hormone III (JH) production (Tobe and Stay, 1985;Gadot et al, 1989a;Gadot et al, 1989b;Gadot et al, 1991) (for reviews, see Schal et al, 1997;Treiblmayr et al, 2006). As the major gonadotropic hormone, JH is produced and released by the CA in a stage-specific manner and it paces the female's reproductive rate.…”

“…B. germanica females may obtain and store enough sperm when first mated to last their entire reproductive life of several months (Cochran, 1979). Thus, the first ovarian cycle is unlike subsequent ovarian cycles as females mature sexually, become sexually receptive, and mate during the first preoviposition period (Schal et al, 1997). Because the first ovarian cycle requires social interaction with males, we hypothesized that the female's endocrine system would be affected by social interactions during the first, but not subsequent, ovarian cycle.…”

Effects of larval nutrition on the endocrinology of mosquito egg development

“…In these insects, JH activates and regulates oocyte maturation and vitellogenesis, whereas ecdysteroids secreted by ovaries regulate final stages of egg maturation such as chorionation and oviposition (Davey, 1997;Schal et al, 1997;Strambi et al, 1997). In dipterans studied to date, JH may prime fat body machinery for vitellogenin synthesis, but ovarian ecdysteroids are the principal regulator that increases the rate of vitellogenin synthesis and release into the haemolymph.…”

Insect juvenile hormone: from "status quo" to high society

“…Sexual behavior, however, is more variable than reproductive physiology, and doubts have been raised whether JH acts as a true regulator for all aspects of female sexual behavior, or whether, at least in some cases, it merely plays a permissive role. In Blattella germanica, production and release (calling) of sex pheromone by the females occurs in close correlation with an increase in JH synthesis (35). However, a further increase in CA activity, as was observed after transfer of male factors during copulation, curtailed calling behavior and sexual receptivity.…”