title: Evidence for the presence of a threshold weight for entering diapause in the yellow-spotted longicorn beetle, Psacothea hilaris.
abstract: Under long-day conditions larvae of Psacothea hilaris (Coleoptera: Cerambycidae) pupate after the 4th or 5th instar, while under short-day conditions they undergo 2-4 nonstationary supernumerary molts and eventually enter diapause. To explore the possibility of a threshold weight for entering diapause, P. hilaris larvae were deprived of food on days 0 (day of ecdysis), 4 or 8 of the 4th, 5th and 6th instars under short-day conditions. Within the first 40 days of starvation, 60% of the larvae starved starting on day 0 of the 4th instar died, but all the larvae starved at later stages survived. The incidence of diapause in these survivors was determined by the occurrence of pupation after a temporary chilling at 15 degrees C for 15 days. Diapause incidence increased as the onset of starvation was delayed; from 11% in the larvae starved on day 0 of the 5th instar to 100% in the larvae starved on day 4 and day 8 of the 6th instar. Analysis of the relationship between the initial weight of a respective larva at the onset of starvation and its pupation success revealed that none of the larvae weighing <or=540 mg pupated but all the larvae weighing >690 mg did. This finding suggests the presence of a threshold weight (about 600 mg), below which larvae are incapable of entering diapause. We discuss these findings with reference to the life history of P. hilaris.
authors.affiliation: Laboratory of Applied Entomology, Department of Agricultural and Environmental Biology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Yayoi 1-1-1, Tokyo 113-8657, Japan.
authors.forename: Florence N
authors.initials: FN
authors.lastname: Munyiri
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Shintani
authors.forename: Yukio
authors.initials: Y
authors.lastname: Ishikawa
mesh_terms: D000367:Age Factors; D000818:Animals; D001835:Body Weight / Q000502:physiology*; D001517:Coleoptera / Q000254:growth & development* / Q000378:metabolism; D005247:Feeding Behavior / Q000502:physiology; D005260:Female; D005508:Food Deprivation / Q000502:physiology*; D007814:Larva / Q000254:growth & development / Q000378:metabolism; D008297:Male; D008675:Metamorphosis, Biological / Q000502:physiology*; D011309:Preservation, Biological / Q000379:methods; D011679:Pupa / Q000254:growth & development / Q000378:metabolism; D016019:Survival Analysis; D013696:Temperature; D013997:Time Factors