<i>Trypoxylus dichotomus</i> larval response to humus, conspecifics and synthetic CO₂

<p>(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 [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0141733#pone.0141733.ref011" target="_blank">11</a>]. 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 (<i>P</i> < 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.