Cuticular hydrocarbons C14-C36 are potential contact pheromonal elements modulating some behaviors in Zygogramma bicolorata (Coleoptera: Chrysomelidae)

Chrysomelid beetle, Zygogramma bicolorata (Pallister, 1953) (Coleoptera: Chrysomelidae), is an important biocontrol agent for the weed Parthenium hysterophorus. The insect spends its whole life on the same plant, which acts as an essential site for feeding, mating and oviposition. These insects were studied for repeated mating, either to same or different mates, and the results indicated both polyandrous and polygamous mating with same-pair mating preferences. Apart from this, a preliminary bioassay was performed individually for both the sexes to detect the presence of contact pheromones. These chemicals, ranging from C-14 to C-36 and often known as cuticular hydrocarbons (straight and branched), were further identified by reading their mass spectra. Although the hydrocarbon profiles of males and females resembled each other qualitatively, the compounds showed a significant difference with respect to their relative proportions. The antennal response to some of the corresponding synthetic straight chain alkanes (Pentacosane, Hexatriacontane, Docosane, Tetracosane, Heneicosane, Hexacosane, Octadecane, Eicosane and Tetratriacontane) were also tested using electroantennography (EAG) at four different concentrations (0.1%, 0.01%, 0.001% and 0.0001%). The mean EAG response obtained was observed to be sex dependent for all compounds tested. The antennae of female responded strongly to these compounds with Tetratriacontane eliciting the highest response of - 0.684 mV at the concentration 0.01%. The difference in the responses may be attributed to the differences in the release rates of these compounds and the sensitivity of antennal responses between the sexes.

Automated summary

Chrysomelid beetle Zygogramma bicolorata is an important biocontrol agent for the weed Parthenium hysterophorus, exhibiting both polyandrous and polygamous mating preferences. Female antennae showed stronger responses to certain synthetic compounds, potentially due to differences in release rates and sensitivity between sexes. The study highlights the complexity of insect mating behavior and the role of chemical communication in species interaction.