Body size determination in insects: a review and synthesis of size‐ and brain‐dependent and independent mechanisms

Abstract

Body size determination requires a mechanism for sensing size and a mechanism for linking size information to the termination of growth. Although the hormonal mechanisms that terminate growth are well elucidated, the mechanisms by which a body senses its own size are only partially understood; most of this understanding has come from the study of the mechanisms that control insect moulting and metamorphosis. We first review and discuss advances in our understanding of the physiological mechanisms by which insect larvae sense their size. Second, we present new findings on how larvae in which the size-sensing mechanism has been disrupted eventually terminate growth (in a size-independent manner). We synthesize recent insights into the genetic and molecular mechanisms of ecdysteroid regulation in Drosophila melanogaster with developmental physiology findings in Manduca sexta, paving the way for an integrated understanding of the mechanisms of body size regulation.

Autocrine regulation of ecdysone synthesis by β3-octopamine receptor in the prothoracic gland is essential for Drosophila metamorphosis

“…S5). Notably, 60 hAH is the critical period during which larvae attain CW under nutrient-rich conditions (2,13,14). As noted above, when larvae are starved before attainment of CW, they are unable to transit into the prepupal stage (2,13,14).…”

“…As noted above, when larvae are starved before attainment of CW, they are unable to transit into the prepupal stage (2,13,14). By contrast, starved larvae can successfully transit to prepupal/pupal stage without developmental delay once they have attained CW by growing beyond the critical period (∼56 hAH) under nutrient-rich conditions in standard Drosophila medium (13,14). Thus, we hypothesized that Octβ3R signaling acts downstream of the body-size checkpoint, or attainment of CW, to allow the larval-prepupal transition.…”

“…Notably, 60 hAH is the critical period during which larvae attain CW under nutrient-rich conditions (2,13,14). As noted above, when larvae are starved before attainment of CW, they are unable to transit into the prepupal stage (2,13,14). By contrast, starved larvae can successfully transit to prepupal/pupal stage without developmental delay once they have attained CW by growing beyond the critical period (∼56 hAH) under nutrient-rich conditions in standard Drosophila medium (13,14).…”

“…defined as the minimum larval size at which starvation no longer delays the larval-prepupal transition (2,13,14). In Drosophila, both checkpoints occur almost simultaneously, making it difficult to distinguish them (2).…”

“…For example, at 56 hAH, early third-instar larvae attain the minimal viable weight (MVW), at which sufficient nutrition is stored in larvae to ensure their survival through metamorphosis (2,13,14). After attaining MVW, larvae pass another checkpoint, critical weight (CW),…”