Differential activity of non-fluorinated and fluorinated analogues of the European corn borer pheromone

Abstract

The differing antagonist activity of (Z)-13-hexadecen-2-one (Z11 -14 : MK, 1) and its 1,1,1-trifluoro derivative (Z11 -14 : TFMK, 2), two closely related analogues of the European corn borer pheromone Ostrinia nubilalis (Z strain), and their rationale is reported. Both chemicals exhibited some electrophysiological activity, and topical application of 10 pg of pheromone analogue on male antennae was sufficient to induce significantly lower depolarization responses to the pheromone versus untreated insects. In a wind tunnel, the number of European corn borer males attracted to sources containing mixtures of 1 + pheromone in ratios ! 1 : 1 was significantly lower than the number attracted to a source containing pheromone alone. Source contact behaviour was dramatically impaired when the 1 + pheromone blend reached a ratio of 10 : 1, in which only 2 % of males displayed source contact in the presence of antagonist. When compound 1 was present at the source, males usually flew upwind with occasional downwind reversals; when compound 2 was present at the lure, males performed wider crosswind reversals, with little progress toward the source. In the field, traps baited with mixtures of both compounds with the pheromone in ratios of 5 : 1 and 10 : 1 elicited a significantly decreased number of male catches. In esterase inhibition assays, compound 2 was a potent inhibitor (IC 50 = 70 nM), whereas the nonfluorinated compound 1 was not. The different activity of both compounds is presumed to be due to different mechanisms of action; considerations for using methyl ketone analogues as new behavioural antagonists of the pheromone are outlined.

Synthesis of allylic trifluoromethyl ketones and their activity as inhibitors of the sex pheromone of the leopard moth, Zeuzera pyrina L. (Lepidoptera: Cossidae)

“…A mixture of TFMKs 3 and 4 in the same ratio (96:4) as the corresponding components in the pheromone blend did not result in a significant difference in activity in comparison with the major analogue 3 alone. The present field results confirm the antagonist activity of other TFMK analogues of the pheromone that was previously recorded on S. nonagrioides ,16 O. nubilalis 40, 41 and Cydia pomonella (L.) 17. Moreover, in large‐scale field experiments, application of ( Z )‐11‐hexadecenyl trifluoromethyl ketone, an analogue of the S. nonagrioides pheromone, yielded a noticeable reduction in damage caused by this pest and by the sympatric species O. nubilalis , both in the number of plants attacked and in the number of larvae found per plant 42…”

“…Pheromone inhibitors, as analogues of the natural pheromones, have been used in mating disruption experiments for pest control 43. The present authors have demonstrated in recent years that TFMKs are potent antagonists of the pheromone in the field and good inhibitors in electrophysiology and behaviour in the laboratory 16, 17, 38–42. In addition, although it has not been determined in antennal extracts of Z. pyrina , these chemicals displayed a remarkable antiesterase activity in S. littoralis ,11, 14 S. nonagrioides 44 and O. nubilalis.…”

“…The non‐fluorinated analogue (OTP) did not affect any of the EAG parameters, confirming the key role played by fluorine atoms in this type of chemical 39, 40. In the European corn borer Ostrinia nubilalis (Hübner), the TFMK analogue of the major component of the pheromone inhibited the EAG response to the natural attractant in a dose–response manner, and 10 pg of the ketone was sufficient to promote a 77% inhibition response 40…”

Plant volatiles challenge inhibition by structural analogs of the sex pheromone in Lobesia botrana (Lepidoptera: Tortricidae)

“…Thus, TFMK analogs of the pheromones of S. nonagrioides and C. pomonella inhibit pheromone response at 1:1 pheromone : analog ratio (Bau et al, 1999;Giner et al, 2009), whereas for O. nubilalis the corresponding analog was active at the minimum ratio of 1:5 (Riba et al, 2005;Solé et al, 2008b). In the processionary moth T. pityocampa, a structural TFMK analog, in which the acetate group of the pheromone was replaced by the CH 2 COCF 3 group, a 5% blend with the pheromone decreased the close approach and source contact behaviour (Quero et al, 1995).…”

“…Thus, while some chemicals exert a remarkable inhibition of male behavioural responses to the pheromone in a wind tunnel, e.g. in Heliothis virescens (F.) (Albans et al, 1984) and O. nubilalis (Solé et al, 2008b), other reports indicate modest electrophysiological inhibitory activity, as in the turnip moth Agrotis segetum Denis & Schiffermüller (Liljefors et al, 1984). In the processionary moth, the MK analog blocked the electroantennogram (EAG) responses after pre-exposure of males to vapour of the chemical (Parrilla & Guerrero, 1994).…”