Changes in defense allomone compositions of Eutrichodesmus elegans and Eutrichodesmus armatus (Polydesmida: Haplodesmidae) during different stages of their life cycles

Abstract

A mixture of E- and Z-(2-nitrovinyl)benzenes is a known allomone of two adult haplodesmid millipedes, Eutrichodesmus elegans (Miyosi) (Polydesmida: Haplodesmidae) and Eutrichodesmus armatus (Miyosi), as is (2-nitroethyl)benzene in E. armatus. However, the proportions of these compounds have not yet been studied in detail at the nymph stage. In the present study, the ratios of these three nitro compounds were shown to change during ontogenetic development. (2-Nitroethyl)benzene was newly detected as the second major component of the mixture in both species at stage I, just after eggs hatched (mean 43.0% in E. armatus and 7.8% in E. elegans), decreasing rapidly to less than 0.1% during growth. These changes occurred in a species-specific manner; field-collected E. armatus maintained a characteristic mixture of E- and Z-(2-nitrovinyl)benzenes (59.9–98.2 and 40.0–1.4%, respectively) during all stages including the adult stage. On the other hand, E. elegans contained E-(2-nitrovinyl)benzene as the major component (98.7–99.7%) with Z-(2-nitrovinyl)benzene as a trace component (less than 1.2%), while a minute amount of (2-nitroethyl)benzene was always retained during all nymph and adult stages. No volatiles were detected in eggs before hatching, and sequential changes of composition were observed among the three compounds after emergence in both species.