Cuticular hydrocarbon profiles differ between ant body parts:implications for communication and our understanding of CHC diffusion

Insect cuticular hydrocarbons(CHCs)serve as communication signals and protect against desiccation.They form complex blends of up to 150 different compounds.Due to differences in molecular packing,CHC classes differ in melting point.Communication is especially important in social insects like ants,which use CHCs to communicate within the colony and to recognize nestmates.Nestmate recognition models often assume a homogenous colony odor,where CHCs are collected,mixed,and redistributed in the postpharyngeal gland(PPG).Via diffusion,recognition cues should evenly spread over the body surface.Hence,CHC composition should be similar across body parts and in the PPG.To test this,we compared CHC composition among whole-body extracts,PPG,legs,thorax,and gaster,across 17 ant species from 3 genera.Quantitative CHC composition differed between body parts,with consistent patterns across species and CHC classes.Early-melting CHC classes were most abundant in the PPG.In contrast,whole body,gaster,thorax,and legs had increasing proportions of CHC classes with higher melting points.Intraindividual CHC variation was highest for rather solid,late-melting CHC classes,suggesting that CHCs differ in their diffusion rates across the body surface.Our results show that body parts strongly differ in CHC composition,either being rich in rather solid,late-melting,or rather liquid,early-melting CHCs.This implies that recognition cues are not homogenously present across the insect body.However,the unequal diffusion of different CHCs represents a biophysical mechanism that enables caste differences despite continuous CHC exchange among colony members.

Red imported fire ants(Hymenoptera:Formicidae)cover inaccessible surfaces with particles to facilitate food search and transportation

Eusocial insects have evolved diverse particle-use behaviors.A previous study reported that red imported fire ants,Solenopsis invicta Buren,deposited soil particles on substances treated with essential balm,a fire ant repellent.We hypothesized that S.invicta modifies inaccessible surfaces by covering them with soil particles to facilitate food search and transportation.Here,laboratory experiments were conducted to study the particle-covering behavior of.S.invicta in response to viscose surfaces or surfaces treated with essential balm or liquid paraffin in the presence of real food(sausage)or non-food objects(acrylic plates).S.invicta workers deposited significantly more soil particles on these three types of treated surfaces than on untreated surfaces.In addition,significantly more particles were relocated on viscose and parafTin-smeared surfaces in the presence of food than in the presence of non-food objects.The particle-covering behavior on viscose surfaces was also observed in the field.Interestingly,when no soil particles were available,ants searched and transported food on viscose surfaces only if the surfaces were artificially covered with sufficient quantities of soil particles but could not do so on viscose surfaces without soil particles or with insutTicient quantities of soil particles.In addition,ants actively relocated particles to cover viscose surfaces if the transportation distance was within 200 mm,whereas significantly fewer particles were relocated at longer transportation distances(400 mm).Our study provides a novel example of particle use by fire ants during foraging.