Apidologie 35 (2004) 403-410
DOI: 10.1051/apido:2004023

A semiochemical from larval food influences the entrance of Varroa destructor into brood cells

Francesco Nazzi, Norberto Milani and Giorgio Della Vedova

Dipartimento di Biologia Applicata alla Difesa delle Piante, Università di Udine, via delle Scienze 208, 33100 Udine, Italy

(Received 3 April 2003; revised 27 October 2003; accepted 3 December 2003)

Abstract - Chemical stimuli responsible for the biological activity of bee larval food on Varroa destructor were studied both in the laboratory and under natural conditions. Loss of activity after neutralization and air entrainment experiments suggested that active substances were acidic and volatile. Linear, branched and aromatic carboxy-acids, as well as hydroxy-acids, were identified by GC-MS and SPME-GC-MS analysis in organic larval food extracts. The low molecular weight carboxy-acids identified were tested in a laboratory assay using a four-well arena. All the acids tested were inactive with the exception of 2-hydroxyhexanoic acid; comparison with related compounds and dose-response studies confirmed the activity of this acid at 10 and 100 ng per well showing that this is a semiochemical for the mite. One hundred nanograms of 2-hydroxyhexanoic acid applied to worker brood cells before capping increased by 36% the number of mites per cell in the treated brood compared to the control cells.

Key words: 2-Hydroxyhexanoic acid / cell invasion / larval food / semiochemical / Varroa destructor

Corresponding author: Francesco Nazzi francesco.nazzi@uniud.it

© INRA, EDP Sciences, DIB, AGIB 2004