Codling moth mating disruption field trials with TNO dispensers

Job W. Klijnstra and Jan J. de Vlieger

• Introduction
• Materials and methods
• Results and discussion
• References

Key words - sex pheromone, mating disruption, controlled release dispensers, (E,E)-8,10-dodecadien-1-ol, pome fruit orchards, Cydia pomonella, Tortricidae, Lepidoptera

Introduction
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Practical use of insect pheromones in pest control is primarily determined by the availability of controlled release devices. Requirements for suitable pheromone dispensers are high: protection of the (expensive) active ingredient(s) from preliminary environmental degradation and delivery of effective concentrations of pheromone for prolonged periods of time are both highly desirable. For monitoring dispensers release rate of pheromone in its natural composition should neither be too low nor too high. For mating disruption dispensers, the effective release period preferably should be long enough to cover the flight season of the target insect.

Our laboratory has developed a novel controlled release technology that can be used for a large variety of volatile substances (Derks 1991; Smit et al. 1991). During the last five years prototype dispensers for a variety of insect pests have been prepared and tested in the field for their release profile and biological efficacy (Klijnstra & de Vlieger 1994). Major effort has been put on the development of a pheromone dispenser that can be effectively used for mating disruption of the codling moth, one of the most devastating orchard pests occurring worldwide. Preliminary field tests with the first prototypes were carried out in 1990 to 1992 in Spain in cooperation with Servei Proteccion dels Vegetals in Barcelona and in The Netherlands in cooperation with IPO-DLO, Wageningen and Denka International, Barneveld. The results of these trials were reported at the IOBC meeting in Chatham, UK (de Vlieger & Klijnstra 1993).

From 1993 onwards, TNO-technology based mating disruption dispensers for control of codling moth have been tested on more than 120 ha at various locations all over the world. Partners involved with these field tests were: L. Anshelevich, Volcani Center, Bet Dagan, Israel; A. K. Minks, IPO-DLO Wageningen, The Netherlands; P.W. Weddle, Hansen & Associates Consultants, California, USA; A. Knight, Yakima Agricultural Research Laboratory (USDA-ARS) and J. F. Howell, Superior Ag Products, Inc., USA, Washington; E. Navarro, GRCETA, France; C. Ioriati, Instituto Agrario, Trento and A. Pacini, Sipcam S.P.A., Italy; P. J. Charmillot, Federal Agricultural Research Station, Changins, Switzerland; Babolna Bioenvironmental Center, Budapest, Hungary; Sandoz Agro, South Africa. Here, a summary of the results of these field tests with regard to dispenser performance is reported.

Materials and methods
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The novel technology is based on crosslinked polymeric matrices prepared by radiation curing (UV or g-radiation) of acrylated prepolymers. The pheromone components and, if necessary, protective agents like UV-absorbers and anti-oxidants, are added to the pre-polymer (mixture) prior to polymerization. After curing a solid, socalled monolithic matrix is obtained. Variation in matrix composition, i.e. the crosslink density of the matrix is the leading principle in designing appropriate dispensers for specific pheromones or purposes. In addition, the release rate can be adjusted by variation in pheromone loading and surface/volume ratio of the dispenser. Dispensers can be loaded with pheromones up to 60% w/w and can be produced in various configurations.

Codling moth dispensers were prepared in flat sheets of 0.3 cm which, after curing with g-radiation, were cut in small square wafers measuring 2.5 x 2.5 cm. The wafers were stitched to plastic clips which could be hung on branches of the trees. Dispenser density in each plot was approx. 500 dispensers/ha. Pre-test chemical analyses showed that each dispenser contained 200 to 230 mg of codlemone (> 97 % (E,E)-8,10-dodecadien-1-ol). In all experimental plots, field exposed dispensers were recollected at a regular scheme for determination of residual pheromone content by means of Soxhlet extraction and GC analysis.

Results and discussion
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In 1993, field collected dispensers from four different locations (Washington, Wageningen, Israel and Switzerland) showed consistent, almost linear release profiles over a periods of more then 140 days. A season long release was thus obtained. Biological performance of the dispensers varied with the location, good control was achieved in Wageningen and Israel whereas in Washington and Switzerland control was not optimal due to various reasons.

In Israel, comparative trials were carried out in 1993 in apple and pear orchards. Table 1 gives the results of these tests. In pheromone treated plots, trap catch reduction was clearly observed and both pheromone systems tested gave good control without any chemical treatments during the season.

In 1994, TNO codling moth dispensers were tested in field trials on 52 ha in total. The results are given in Table 2. In almost all plots monitoring traps caught significant numbers of moths. In California during the previous season (1993) codling moth damage approximated 2.5% in the 1994 mating disruption plot. Therefore, a combination program of azinphosmethyl and mating disruption was carried out to reduce this population. Reduced trap counts in later generations indicated that this was indeed accomplished. Fruit damage at harvest was less than 1% in both types of plots. TNO dispensers showed an average release of approximately 1 mg/dispenser/day over 176 days.

In Hungary, trials were started approx. five weeks after start of moth flight. Also here, during the season an additional treatment with azinphosmethyl was necessary. At harvest, the combined pheromone and insecticide treatment showed substantially reduced damage when compared with insecticide alone. An average release of 0.8 mg/dispenser/day was found.

From the Italian trials in 1994 no trap catch data were received. Damage inside the plot was very low, but was very high at some particular spots along the border.

In France, mating disruption trials were started one month after beginning of moth flight. One insecticide treatment was applied prior to the start of the trial, later on three partial treatments were necessary. Adjacent control blocks received multiple chemical treatments during the season. Trap shut down was complete in the pheromone block, damage level at harvest was very low. Release data from the first 45 days indicate an average release of 2.2 mg/dispenser/day.

In South Africa trials in three comparable plots were initiated just prior to beginning of moth flight. Two of the three sites contained high moth levels and received additional insecticide treatments. The third block received pheromone application only. In this last block, trap shut down was complete. Because of the long flight season in South Africa and very high day temperatures anticipated, a second set of dispensers was applied after approximately 4 months. Average release appeared to be 0.8 mg/dispenser/day. Fruit damage was found to be minor (in the first two plots) to zero (in the final plot).

In 1995 mating disruption trials were carried out at a total acreage of 45 ha. The results are shown in Table 3.

In California trials were conducted in the same blocks as in 1994. No trap shut down was observed with 10-mg lures. Numbers of moths caught were quite high. Nevertheless, in the pheromone block only one chemical treatment was required, instead of four in 1994, to give adequate control. The control block received two sprays. Overall harvest damage was less than 1%, similar to 1994. Average release of dispensers was 0.9 mg/dispenser/day.

In Hungary, the infestation level in experimental plots was again quite high as can be deduced from trap catches in Table 3. No trap shut down was observed in traps containing 10-mg lures. Mating disruption combined with IGR treatment showed substantially reduced damage when compared to conventional treatment alone. Damage levels in 1995 were higher than those in 1994. Dispenser release on average was found to be 0.8 mg/dispenser/day.

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Also in France, trap catches in the pheromone plots were found to be higher than those of 1994. Organophosphate treatment was applied at mid-season. Damage level also appeared to be higher than in 1994, reaching 5.5% at some particular spots. Average release of dispensers amounted to approximately 1 mg/dispenser/day.

In Italy trap catch data in an untreated plot suggest that 1-mg lures are more attractive than 10-mg lures. Data were based on one trap of each type only, therefore a factor like trap placement may have had a significant influence as well. Damage figures in this trial relate to mid-season damage which appeared to be low in all three plots. Even in the untreated plot, with significant trap catch, damage was not higher than 1.2%. Average release of dispensers approximated 1.1 mg/dispenser/day.

In Switzerland initial populations were low, no preventive insecticide treatments were necessary. Trap catch as well as fruit damage appeared to be low: 0.7% is well below economic threshold. Average release rate of dispensers was found to be 1.3 mg/ dispenser/day.

Release profiles of field exposed dispensers have shown a very gradual release over a period of 4 to 5 months which, for most countries in the world, covers the whole flight season of codling moth. During this period excellent protection of codlemone was found. The results of all trials generally indicate the proper performance of TNO dispensers for sustained release of codlemone and sufficient biological efficacy. Also at higher initial pest populations good control can be obtained when application of mating disruption is combined with supplementary insecticide treatment prior to or during the season. From technical point of view the TNO system is ready for commercialisation and market introduction. The system is very versatile and is suitable for preparing dispensers with a variety of other pheromones and volatile compounds (Klijnstra & de Vlieger 1994; de Vlieger & Klijnstra 1994). A production scenario of dispensers is currently under development and the technology is available for licensing.

References
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Derks PSM (1991) European Patent No 0 410 530 A1

Klijnstra JW, de Vlieger JJ (1994) Release profiles of novel monolithic pheromone dispensers. Poster presentation at 1st int Symp Insect Pheromones, March 1994, Wageningen, The Netherlands

Smit CN, Derks PSM, van Gils WJCG, de Raat WK (1991). Proc int Symp ctrl Rel bioact Mat 18, 81

de Vlieger JJ, Klijnstra JW (1993) Mating disruption of codling moth and fruit tree leafrollers in apple orchards with TNO dispensers. IOBC wprs Bulletin 16 (10), 99-103

de Vlieger JJ, Klijnstra JW (1994) Novel polymer delivery systems for insect attractants. Proc int Symp ctrl Rel bioact Mat 21, 73-74
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