Pamela RAMIREZ-LUCAS-a, Didier ROCHAT-a,
Christian MALOSSE-a, Pierre ZAGATTI-a, Charles DESCOINS-a,
Kenji MORI-b
a-Unité de Phytopharmacie et Médiateurs Chimiques, INRA,
Route de Saint-Cyr, 78026 Versailles cedex, FRANCE
b-Department of Agricultural Chemistry. The University of
Tokyo,1-1-1, yayoi, Bunkyoku, Tokyo 113, JAPAN
Key-words. Coleoptera, Curculionidae, Metamasius hemipterus, aggregation pheromone, identification, field trapping
Metamasius hemipterus is a neotropical Rhynchophorinae weevil. The species is a sugarcane pest, occasionally met in banana and pineapple crops. It has recentIy been suspected to be a vector of the Red ring disease to oil palm trees in Colombia.
Through volatile collections and analytical methods (GC, GC-MS. H-NMR), five hydroxylated aliphatic molecules were identified as components of the effluvia released by M. hemipterus males: 4-methyl-5-nonanol (1), 2-methyl-4-heptanol (2), 2methyl-4-octanol (3), 5-nonanol (4) and 3-hydroxy-4-methyl-5-nonanone (5) 1,2 1 was the major component, accounting for 80- 95% of the blend. Enantioselective synthesis and GC on chiral phase (Cydex-B) showed natural 1 to be pure (4S,5S) isomer 3. Behavioural results indicated that the non natural isomers were not inhibitor4. 1 was known as the major pheromone compound of related Rhynchophorus species2,5
The natural male effluvia elicited aggregation behaviour of M. hemipterus in a 4-way olfactometer at 2-male.day.equivalent doses. The natural pheromone was especially active on virgin females, giving weaker responses in both mated and virgin males2
The five synthetic components (racemic mixtures) were tested in the field5. The pheromone compounds were released from heat-sealed polyethylene bags containing the pheromone compounds, either pure or diluted in paraffin oil.
1 was unable to lure M. hemipterus when tested alone (10 mg/day). It synergistically attracted both sexes of M. hemipterus when associated to sugarcane (SC) The addition of 2 or 3 (0.5 mg/day) to 1 (5 mg/day) plus SC was required to obtarn maximum field catches while 4 or 5 (0.5 mg/day) did not enhance weevil attraction
Redundancy was observed between compounds 2 and 3. The sex-ratio of the lured weevils was significantly modifed by the qualitative composition of the pheromone blends. Both phenomena are originally reported here in a Coleopteran species 3 alone plus SC attracted sign)ficantly more females than SC. exhibiting a clear sexual role. At the opposite 5 tended to balance the sex-ratio.
The results should significantly improve the control of M. hemipterus populations Further investigations are underway to optimise the synthetic lures
References