Precocene II has no anti-juvenile hormone effects in adult honey bees

Hormonal pleiotropy helps maintain queen signal honesty in a highly eusocial wasp

In insect societies, both queens and workers produce chemicals that reliably signal caste membership and reproductive status. The mechanisms that help to maintain the honesty of such queen and fertility signals, however, remain poorly studied. Here we test if queen signal honesty could be based on the shared endocrine control of queen fertility and the production of specific signals. In support of this “hormonal pleiotropy” hypothesis, we find that in the common wasp, application of methoprene (a juveline hormone analogue) caused workers to acquire a queen-like cuticular hydrocarbon profile, resulting in the overproduction of known queen pheromones as well as some compounds typically linked to worker fertility. By contrast, administration of precocene-I (a JH inhibitor) had a tendency to have the opposite effect. Furthermore, a clear gonadotropic effect of JH in queens was suggested by the fact that circulating levels of JH were ca. 2 orders of magnitude higher in queens than those in workers and virgin, non-egg-laying queens, even if methoprene or precocene treatment did not affect the ovary development of workers. Overall, these results suggest that queen signal honesty in this system is maintained by queen fertility and queen signal production being under shared endocrine control.

No effect of juvenile hormone on task performance in a bumblebee (Bombus terrestris) supports an evolutionary link between endocrine signaling and social complexity

A hallmark of insect societies is a division of labor among workers specializing in different tasks. In bumblebees the division of labor is related to body size; relatively small workers are more likely to stay inside the nest and tend ("nurse") brood, whereas their larger sisters are more likely to forage. Despite their ecological and economic importance, very little is known about the endocrine regulation of division of labor in bumblebees. We studied the influence of juvenile hormone (JH) on task performance in the bumblebee Bombus terrestris. We first used a radioimmunoassay to measure circulating JH titers in workers specializing in nursing and foraging activities. Next, we developed new protocols for manipulating JH titers by combining a size-adjusted topical treatment with the allatotoxin Precocene-I and replacement therapy with JH-III. Finally, we used this protocol to test the influence of JH on task performance. JH levels were either similar for nurses and foragers (three colonies), or higher in nurses (two colonies). Nurses had better developed ovaries and JH levels were typically positively correlated with ovarian state. Manipulation of JH titers influenced ovarian development and wax secretion, consistent with earlier allatectomy studies. These manipulations however, did not affect nursing or foraging activity, or the likelihood to specialize in nursing or foraging activity. These findings contrast with honeybees in which JH influences age-related division of labor but not adult female fertility. Thus, the evolution of complex societies in bees was associated with modifications in the way JH influences social behavior.

Precocene-I inhibits juvenile hormone biosynthesis, ovarian activation, aggression and alters sterility signal production in bumble bee (Bombus terrestris) workers

Juvenile hormone (JH) is an important regulator of development and physiology in insects. While in many insect species, including bumble bees, JH functions as gonadotropin in adults, in some highly eusocial insects its role has shifted to regulate social behavior including division of labor, dominance and aggression. Studying JH functions across social insect species is important for understanding the evolution of sociality; however, these studies have been limited because of the inability to reduce JH levels without surgically removing its glandular source, the corpora allata. Precocene is known to inhibit JH biosynthesis in several non-social insects, but has been poorly studied in social insects. Here, we tested whether precocene-I can effectively reduce JH levels in Bombus terrestris workers, and examined its effects on their physiology and behavior. Precocene-I treatment of three-worker groups decreased JH titer and ovarian activation, irrespective of the bees' dominance rank within the group, and was remedied by JH replacement therapy. Precocene-I also decreased aggressiveness and increased ester-sterility signal production; these changes were rank-dependent, and affected mainly the most reproductive and the least aggressive workers, respectively, and could not be remedied by JH replacement therapy. These results clearly confirm the role of JH as a gonadotropin and mediator of aggression in B. terrestris, and indicate that JH effects are associated with worker dominance rank. The ability to chemically reduce JH titer provides us with a non-intrusive method to probe the evolutionary changes associated with JH and the hormonal mechanisms that are associated with reproduction and behavior in social insects.