Environmental Factors Affecting Pupation Decision in the Horned Flour BeetleGnatocerus cornutus

Abstract

Social environments often affect the development of organisms. In Tenebrionidae beetles, larval development can be arrested at the final instar stage in the presence of conspecific larvae. This developmental plasticity is considered to be an anti-cannibalistic strategy but the critical environmental determinants and actual effects remain to be elucidated. In this study, we examined the effects of the heterospecific environment, conspecific sexual environment (i.e., presence of conspecific male or female), and abiotic physical stimulation on the pupation decision of the sexually dimorphic horned-flour beetle Gnatocerus cornutus. Additionally, actual anti-cannibalistic or antipredatory effects of developmental arrest were evaluated by analyzing stage-dependent vulnerabilities. When G. cornutus larvae were maintained with a G. cornutus larva, a G. cornutus adult, or T. castaneum adult, the developmental period up to the prepupal stage was significantly elongated, suggesting that the cue is not species-specific. Sexual environment did not affect the timing of pupation in G. cornutus; however, we found that abiotic tactile stimulations by glass beads could repress pupation. We also discovered that prepupal and pupal stages were more vulnerable to cannibalism and predation than the larval stage. These data suggest that G. cornutus larvae use non-species specific tactile stimulation as a decision cue for pupation and it has broader defensive effects against heterospecific predation as well as conspecific cannibalism.

A specific type of insulin-like peptide regulates the conditional growth of a beetle weapon

“…The stock was maintained with wholemeal flour enriched with yeast. The stock populations were reared in plastic containers (diameter, 40 mm; height, 30 mm) in groups of approximately 200 larvae, and they were provided with sufficient culture medium (wholemeal enriched with brewer’s yeast [EBIOS, Asahi Group Foods, Tokyo, Japan]) [67].…”

“…cornutus . Additionally, its pupation is inhibited by larval crowding to avoid being the victim of cannibalism during molting, as is generally the case for Tenebrionidae [67,68]. In our experiment, larvae aged from 30 to 60 days after hatching (approximately 2‒6 mg in weight) were transferred from sufficiently fed culture conditions to unfed solitary conditions (individual wells in a 24-well plate, VTC-P24, VIOLAMO) (Fig 1) [68].…”

“…The larval stages were defined as the days after isolation (e.g., a larva aged 1 day after isolation is referred to as a day-1 larva). Prepupation was visually checked every 24 hours to detect their characteristic L-shaped posture [67] (Fig 1). After the isolation from the stock, large larvae (>4 mg) soon proceeded to the prepupal stage (2‒4 days, Fig 1, S1 Fig), whereas small larvae (<4 mg) took longer for prepupation (3‒8 days).…”

Histone deacetylases control module-specific phenotypic plasticity in beetle weapons

“…Our stock population of G. cornutus originated from adults collected in Miyazaki City (31°54′, 131°25′), Japan, and was maintained at the National Food Research Institute and Okayama University (24). G. cornutus was reared as described previously (54).…”

“…Dosage was optimized to produce maximal nonlethal effects by the stated criteria (TSA: 46 ng per larva, 5AzaC: 3.48 μg per larva), and drugs were injected into the larvae by using Nanoject II (Drummond Scientific) under CO 2 anesthesia. The injected larvae were individually isolated in 24-well culture plates (Thermo Scientific), so that they could develop into prepupae (the adult morphogenetic stage) within 3-4 d (36,54). No food was provided after the treatment.…”