Maruca pheromone trap Web pages

Our earlier work (Downham et al., 2003) had developed an attractive pheromone blend - EE10,12-16:Ald, EE10,12-16:OH and E10-16:Ald in the ratio 100:5:5 at least in Benin. In relation to the lures themselves we had found no significant differences in catches using polyethylene vials or rubber septa, or between lures containing 0.01 and 0.1 mg of pheromone, but considered 0.1 mg polyethylene vials to be the lures of choice due to their greater expected longevity under field conditions.

We now set out to optimize other aspects of the pheromone lures and traps (Downham et al., 2004). To minimize eventual costs to farmers we sought to develop traps which would not have to be imported – which could be made locally, by farmers if necessary.

We compared several different trap designs. A locally fabricated water-trap made from a five litre plastic jerry-can was found to be superior to commercial funnel- and sticky-trap designs. Not only are the jerry-can traps relatively much cheaper than imported, commercial designs (less than US$1.00 compared to US$3.00 or more), they are easy to construct and robust in use.


a) 1.5 litre bottle trap		(b) 2 litre plastic jerry-can trap


(c) commercial sticky delta trap		(d) locally made 5 litre jerry-can trap

Cost of the lures would also be an important practical issue. Diene compounds such as EE10,12-16:Ald, the major blend component, are susceptible to oxidation of the double bond, with subsequent loss of attractiveness. However, we observed that shielding of lures from the adverse effects of sunlight, by means of aluminium foil, did not increase trap catches of M. vitrata so this does not seem an important factor, while no loss of attractiveness was observed for 0.1 mg polyethylene vial lures up to four weeks old.

Mean catches per trap of M. vitrata males in delta traps baited with lures of different ages, and shielded or unshielded from sunlight. All lures contained the 100: 5: 5 blend. Error bars = standard errors of the means. [Data from: Downham et al. (2004)]

Another factor, the degree of isomeric purity of the EE10,12-16:Ald and EE10,12-16:OH blend components, was also investigated. Lures with purities in the range 73 – 99% were tested and had no significant effect on captures. These results are significant from the practical view-point because the cost of commercially produced lures is affected by the extent of isomeric purification required. If, as experience shows, a lower level of purity can be used without a marked loss of attractiveness, this will help to ensure the economic viability of pheromone trap monitoring.

From these results an effective and practical trapping system for M. vitrata has now been developed for the first time. In Benin, polyethylene vial lures are effective for up to 4 weeks under field conditions, and the precise dose, blend ratio or isomeric purity of the pheromone is not critical in achieving catches in the field.

To utilise traps at a practical level the establishment of some relation between trap-catches of adults and the incidence of larval attack in cowpea fields is necessary.

Monitoring of trap catches and larval infestations in un-sprayed farmers’ fields quickly showed a potentially useful temporal relation between the two. As the figure shows, for fields sown around the same time, moth captures typically do precede larval infestations by several days enabling farmers to determine when they might need to spray. In the example shown, the first, low infestations occurred 7 days after the initial trap-catches, although in other areas the time-lag may be less.

Illustrative pooled results of cumulative trap-catches (bottom) and cumulative infestations of eggs and larvae in flowers and pods (top), for six early-planted on-farm sites, first season Savè, 2000 [Unpublished project data].

An additional finding was that a possible alternative predictive measure, that of the appearance of flowers in the crop, tended to give a much shorter warning period of infestations than initial trap captures.

Through empirical testing during several on-station and farmer field school trials we gradually developed a trap-based threshold for spraying against M. vitrata in cowpea in Benin. The threshold is reached when the cumulative average captures for a group of at least six traps reaches two moths per trap. Application of insecticide is advised three days (3 d) after this threshold is reached. For example, in one on-station trial we compared thresholds triggered at two and five moths per traps, each with spray delays of three (3 d) or six days (6 d) combined with applications of a conventional (‘Decis’ = deltamethrin) and botanical (aqueous neem leaf extracts) pesticide. These were compared to treatments in which insecticides were applied twice according to crop stage - when 25% of plants had flowers and pods, respectively. Lower infestations in pods were obtained with the 2-moth threshold, and with a 3-day application delay and the highest yield among the botanical pesticide treatments was obtained with the 2-moth/3-day threshold approach.

Mean total cumulative M. vitrata infestations per 20 pods (± S.E.) in on-station trial at IITA, Cotonou, Benin, May – August 2002. Four replications per treatment [Unpublished project data].

Now, based on the threshold development we have produced a leaflet and posters describing the practical installation and use of the pheromone traps, involving this threshold.

Since late 2002 around 500 farmers in 26 different villages in Benin and Ghana have been involved in testing and refining the use of pheromone traps in the control of M. vitrata. A co-operative and flexible approach to this has been evolved within the framework of farmer field schools operating under the auspices of project partners GOAN and CRI in Ghana and OBEPAB and INRAB in Benin (INRAB farmer field schools in Benin are also associated with the IITA-managed regional PRONAF project).

Individual farmers operate six traps in cowpea fields distributed around the village; when the threshold date is determined from the cumulative average catch of two moths per trap, spraying within three days is then advised, but farmers are free to decide, collectively, the best control agent to apply for each field - botanical or conventional pesticide, and exactly when to apply it, taking account of the overall pest situation.