Acaricidal activity of natural monoterpenes on Tyrophagus putrescentiae (Schrank), a mite of stored food.

Seven natural monoterpenes (pulegone, eucalyptol, linalool, fenchone, menthone, alpha-terpinene and gamma-terpinene), out of 13 tested, were shown to possess a high acaricidal activity by vapour action against mobile stages of Tyrophagus putrescentiae. Of these seven, pulegone, menthone, linalool, and fenchone yielded LC(90) values of 14 µl/l or below. However, no effect was recorded on egg hatching. Interestingly, the larvae and males of T. putrescentiae presented a mortality rate significantly higher than females (about 2-fold) when exposed to the same vapour concentration of the active monoterpenes. The high acaricidal activity recorded on immature and adult stages might be primarily related to desiccation, since dead mites presented symptoms usually considered to be associated with this phenomenon. Moreover, since larvae and males are significantly smaller than females and their surface/volume ratios are higher, they tend to lose relatively more water, thus supporting the notion that the greater acaricidal activity recorded on larvae and males might be primarily related to desiccation. Nevertheless, action by interference with respiratory processes cannot be discarded. The potential of these natural monoterpenes for practical use against mobile stages of T. putrescentiae in warehouses of traditional Spanish dry-cured ham is discussed.