The present invention relates to an inhibitor of an activation of .beta.-glucan recognition protein in a body fluid of an insect comprising a sugar compound comprising plural member of sugar residues, at least one of which have a substituent at the 6-position, the sugar residues being bonded mainly through .beta. 1.fwdarw.3 linkage with one another, a process for inhibiting the activation; an agent for treating the body fluid of an insect, a process for the treatment; a novel agent for measuring peptidoglycan simply and effectively, and a process for the measurement. The present invention is markedly effective in that a reagent, which are obtained form a body fluid of an insect, can easily be obtained.