Pheromones synergism with

A blend of racemic 24, 25, 27, and 29, along with (+)-28 obtained from citronella oil, was prepared and formulated so that the emitted compounds would be in the proportions found from P. cruciferae. The blend was field tested in Canada by Soroka et al. (2005). (Compound 26 was not available in sufficient amounts for inclusion in the study.) They found that the mixture was attractive to both sexes, supporting the original idea that the compounds serve as a pheromone. Furthermore, the blend was synergized by allyl isothiocyanate, a mustard oil from the hosts that was previously found to be attractive to P. cruciferae (see Soroka et al., 2005, for discussion). This biological pattern was like that for the nitidulids, but with completely different chemicals. 

R,R)-8-methyl-2-decanol propanoate (34). Sonnet et al. (35) synthesized the four stereoisomers of this pheromone in high stereoisomeric purity (Table I). Comparison of the captures of WCR males in the field with traps baited with the individual steroisomers and with the racemic mixture demonstrated that the males respond strongly to the (R,R)-isomer and to a lesser extent to the (2S,8R)-isomer. The other two isomers are inactive i.e., they neither attract nor inhibit the response of WCR males, nor do they synergize the activity of the (R.R)-isomer (36). The (R,R)-isomer appears to be as attractive as an equal amount of the natural pheromone in volatiles collected from females. Thus it is possible that the WCR is utilizing a single component pheromone. 

Bioassay of these compounds indicated that both the hydroxy ketones 105 and 108 are about ten-fold more active than the respective parent ketones 104 and 107 of the same chain-length.106 Each of the six pheromone components can independently elicit the complete repertoire of sex response with no synergism... 

Fig. 4.2 Variable effect of host monoterpene concentration on 1. pini attraction to its pheromones. Lower concentrations, equivalent to those in constitutive host tissue, synergize the attractiveness of pine engraver pheromones. High concentrations, equivalent to those occurring during the first few days of induction, inhibit attraction to pine engraver pheromones. (with permission from Blackwell).

---