Development and optimisation of a sex pheromone lure for monitoring populations of saddle gall midge, Haplodiplosis marginata

Abstract

Saddle gall midge, Haplodiplosis marginata (von Roser) (Diptera: Cecidomyiidae), is a sporadic pest of cereals in Northern and Central Europe and is of increasing importance in the UK. Recently, the major component of the sex pheromone produced by adult female H. marginata was reported to be 2‐nonyl butyrate. The importance of absolute configuration on attractiveness, the effects on trap catches of the addition of minor pheromone components, dispenser type, and pheromone loading are described in the development of an optimised pheromone lure with which to trap H. marginata males. In analyses of volatiles collected from virgin female H. marginata by gas chromatography (GC) coupled with electroantennographic recording (EAG) from the antenna of a male H. marginata, two EAG responses were observed. Analyses by coupled GC‐mass spectrometry (MS) indicated these were due to 2‐nonyl butyrate and a trace amount (1%) of 2‐heptyl butyrate. A similar trace amount of 2‐nonanol was detected in GC‐MS analyses but this compound did not elicit an EAG response when the synthetic compound was tested, whereas the other two compounds did. These three compounds were not observed in collections of volatiles made from male H. marginata. The 2‐nonyl butyrate was shown to be the (R)‐enantiomer. In field trapping tests (R)‐2‐nonyl butyrate was at least 10× more attractive to male H. marginata than the racemic compound, and the (S)‐enantiomer was unattractive. Addition of the potential minor components individually or together at the naturally occurring ratios did not increase or reduce the attractiveness of the lure. Polyethylene vials and rubber septa were equally effective as pheromone dispensers, lasting for at least 5 weeks in the field in the UK, although laboratory tests indicated release from the former was more uniform and more likely to last longer in the field. Increasing loading of pheromone in the dispenser increased attractiveness. Traps baited with polyethylene vials containing 0.5 mg of (R)‐2‐nonyl butyrate are recommended for monitoring H. marginata and these are far more sensitive than water or sticky traps currently used for monitoring this pest.

Factors affecting trap catch in pheromone‐based monitoring of saddle gall midge Haplodiplosis marginata (Diptera: Cecidomyiidae)

“…In the final week of trapping, old lures trapped 45% of the number of insects caught by new lures, which is to be expected from the finding that 35–40% of the pheromone remained in the old lures at the end of the experiment. This concurs with earlier experiments where 6‐week‐old field aged lures containing 1 mg of racemic 2‐nonyl butyrate had 0.41 ± 0.02 mg of the compound remaining . Thus, these lures are likely to remain attractive over the entire flight period of H. marginata , which is typically 8–10 weeks .…”

“…Pheromone dispensers were placed in standard red delta traps (Agralan, Wiltshire, UK) containing a removable sticky insert (15 cm x 15 cm). Polyethylene vials (26 mm x 8 mm x 1.5 mm thick; Just Plastics Ltd, London, UK) containing ( R )‐2‐nonyl butyrate (0.5 mg; 98% enantiomeric excess) synthesised as described in Rowley et al . were used as lures for all experiments.…”

“…Ideally, a lure should exhibit a constant rate of release and last for the duration of the insect flight season. In previous work, polyethylene vials loaded with 0.5 mg ( R )‐2‐nonyl butyrate were identified as effective dispensers for the H. marginata pheromone, lasting for at least 4 weeks under laboratory conditions . Here, we determined the effectiveness of the lure over time under typical field conditions.…”

“…identified the major component of the female sex pheromone of H. marginata as 2‐nonyl butyrate. More recently, an effective lure for this pest has been developed, based on the optimised blend and loading of pheromone and dispenser type . For this information to be of practical benefit, however, more information is needed on how best to deploy traps baited with these pheromone lures.…”

Degree-day based phenological forecasting model of saddle gall midge ( Haplodiplosis marginata ) (Diptera: Cecidomyiidae) emergence

“…The sex pheromone of H. marginata has been identified as 2-nonyl butyrate (Censier et al, 2014b) which has led to the development of species specific pheromone traps (Censier et al 2016, Rowley et al, 2017. This advance has made it possible to reliably monitor the emergence and flight activity, providing opportunity to easily study populations in the field (Censier et al, 2016).…”