Juvenile Hormone, Behavioral Maturation, and Brain Structure in the Honey Bee

Abstract

Juvenile hormone regulates metamorphosis in insects, and its effects on the nervous system during the larval-pupal transition have been studied primarily in the hawk moth, Manduca sexta. The effects of juvenile hormone on the nervous system of adult insects have been little studied. Elucidating the role of juvenile hormone during behavioral development in adult honey bees provides an opportunity to study hormone regulation of nervous system structure and function in an insect with a rich behavioral repertoire and social life. A worker honey bee typically lives 30–60 days. During this time, she performs a sequence of different tasks that sustain the colony. A striking behavioral transition typically occurs at about 3 weeks of age. At this time, worker bees stop performing within-hive tasks such as rearing brood and building comb and begin to forage outside the hive. This behavioral development is accompanied by a marked increase in the production of juvenile hormone. The mushroom bodies of the protocerebrum, the region of the insect brain most often associated with learning and memory, also undergo an internal reorganization during behavioral development. High titers of juvenile hormone and an increased volume of neuropil associated with the mushroom bodies are characteristic of the forager. Importantly, the time of the behavioral transition to foraging is not fixed. Individual bees can respond to changing colony or environmental conditions by accelerating or delaying the switch from within-hive tasks to foraging. For example, in the absence of older workers, some bees will undergo precocious development and may forage as early as 4 days of age. These workers also experience a precocious rise in juvenile hormone and an earlier reorganization of the mushroom bodies. Our current studies investigate the roles played by juvenile hormone and experience in shaping the mushroom bodies of the adult honey bee, and the relationship of these changes to the bee's ability to forage successfully. It is proposed that juvenile hormone may mediate neural plasticity in the brains of adult honey bees to support the demanding cognitive task of foraging.

Rapid behavioral maturation accelerates failure of stressed honey bee colonies

“…SCC (24,(40)(41)(42) is an established method for creating a colony with a younger age distribution of foragers. It has been argued that, for many social insects, early foraging by individuals might be a response to individual stress resulting in a shift in the demography of the foraging force (18): SCC provides a social manipulation to reduce the modal age of foragers by reducing social inhibition independent of any pathogen pressure.…”

Developmental and dominance‐associated differences in mushroom body structure in the paper wasp Mischocyttarus mastigophorus

“…In both Apis and Polybia, which are highly eusocial species, the MB calyx:Kenyon ratios are greater in foragers than in nest workers (Farris et al, 2001;O'Donnell et al, 2004). This pattern has been interpreted as reflecting the greater cognitive demands associated with foraging (Fahrbach and Robinson, 1996), and possibly with higher light levels and other stimuli outside the nest.…”

Starvation stress during larval development facilitates an adaptive response in adult worker honey bees (Apis mellifera L.)

“…Vg knockdown amplifies JH titer (Nelson et al, 2007;Wang et al, 2012a,b), resulting in an increase in glucose responsiveness (Amdam et al, 2006b;Wang et al, 2012a), early onset of foraging and a foraging bias for nectar (Nelson et al, 2007). Topical application of a JH analog, methoprene, to young workers increases sucrose responsiveness (Pankiw and Page, 2003), and JH paces behavioral development in workers, as is evident by its ability to induce an earlier onset of foraging (Jaycox et al, 1974;Jaycox, 1976;Fahrbach and Robinson, 1996;Sullivan et al, 2000Sullivan et al, , 2003Chang et al, 2015). In our study, the bees that experienced larval starvation had fewer ovarioles, higher hemolymph JH titer and lower sucrose responsiveness, but had no change in Vg mRNA.…”