Brazilwood sawdust composition confirms different feeding habits of larvae and adult males of the ambrosia beetle Megaplatypus mutatus during excavation

Ambrosia beetles are an emerging threat to forestry ecosystems, attacking native and non-native trees. The brazilwood ( Paubrasilia echinata (Lam.) Gagnon, H.C.Lima & G.P.Lewis) is currently considered the most appropriate material for the manufacture of violin bows due to its unique vibrational properties. An experimental plantation of brazilwood has been attacked by the ambrosia beetle Megaplatypus mutatus Chapuis. In this work, we compared the cell wall carbohydrate composition of brazilwood sawdust produced due to the attack of imagoes (adult males) and larvae of this beetle. We aimed to assess changes caused by the insect and its associated microbiota. Cellulose and xylans represented the main fractions of all materials, and pectin accounted for only 10-15% of the walls. The yield of wall fractions and cell wall composition of the sawdust produced by adult beetles, which is composed of long particles, were quite similar to those found in the material obtained from uninfected trunks indicating that the adult male does not feed on the wood at this stage. In contrast, chemical fractionation of the granular sawdust from larvae showed a lower content of extractable pectins, representing only 50% of the total amount detected in the sawdust produced by adult male beetles. Sugar composition analysis of the pectin fractions of the larval sawdust revealed the loss of arabinosyl, galacturonosyl, and galactosyl residues, indicating that the association between beetle/ambrosia fungus evolves towards the degradation of easily accessible pectic polysaccharides of the cell wall.