Fig 1.
Trypoxylus dichotomus larval response to humus, conspecifics and synthetic CO2
(A) A group of 3rd instar larvae in a microhabitat. Soil above the larvae was removed. (B and C) Schematic representation of the behavioural arena established in a previous study [11]. In (B), the larval response to various amounts of CO2 (or air for the control) was tested. CO2 was pumped through a pipette into the soil using a syringe driver. In (C), larvae were given the choice of 20 mL/h of CO2 or two conspecific larvae in a mesh cage. In both systems, ‘attraction zones’ and ‘non-attraction zones’ were set within 10 cm from each end. (D) The percentage of larvae attracted to air, CO2, highly fermented (HF) humus [against poorly fermented (PF) humus] or to two larvae in a mesh cage. The total number of larvae found in the attraction zone was compared with that of larvae in the non-attraction zone. Asterisks indicate a significant difference (P < 0.05) from 50% (dashed line); analysed using the binomial test. The sample sizes (the sum of the larvae in the attraction and non-attraction zones) were 12, 17, 22, 20, 20, 22, 19, 16, 20, 15, and 16 from left to right.
Fig 2.
CO2 concentration and Trypoxylus dichotomus larval density/presence.
(A) Comparison of soil CO2 concentrations between containers (triangles) with and without insects (circles). The data from eight pairs of replicates are presented in different colours. (B) The relationship between larval density (i.e., the number of larvae in a quadrat) and CO2 concentration in that quadrat. (C) Comparison of soil respiration between containers with (triangles) and without insects (circles). (D) The relationship between larval density and soil respiration.
Table 1.
Larval weight gain under high and low nutrient conditions is density dependent.
The effects of density (1, 3, or 9 larvae/cage) and food quality (highly fermented or poorly fermented humus) on larval weight gain were tested using the LMM. Sex and initial weight were included as covariates, and identity of the mother of each larva was included as a random factor. Following an analysis of pooled data, additional analyses under each nutrition condition were conducted because the interaction term between density and food quality was significant.
Fig 3.
Effect of density on Trypoxylus dichotomus larval growth.
Body weights of 2nd instar larvae reared at low (1 larva/cage), medium (3 larvae/cage), and high (9 larvae/cage) densities when provided poorly fermented (left) or highly fermented (right) humus. Error bars, SE. Letters indicate P < 0.05 in pairwise comparisons analysed by a linear mixed model with Tukey test. Detailed statistical values are presented in Table 1. Sample sizes are shown in parentheses. Error bars, SE.