IOBC wprs Bulletin Vol 22(9), 1999

Application of wide area mating disruption for control of oriental fruit moth Grapholita molesta Busck (Lepidoptera; Tortricidae) migration in victoria, Australia

Alexandre L. Il'ichev, Mofakhar S. Hossain and Peter H. Jerie

Institute of Sustainable Irrigated Agriculture, Tatura, Victoria, Australia

Abstract: The Wide Area Mating Disruption (WAMD) strategy has been applied to improve the protection of orchards against migration of Oriental Fruit Moth (OFM). During 1997-98 season the experimental area over 800 hectares of orchard in the Murray-Goulburn Valley, Victoria was saturated with OFM sex pheromone to test the concept of WAMD. Mating disruption lures called "Isomate OFM Plus"(Biocontrol Ltd.) were applied on all fruit trees including peaches and nectarines, as well as pears, apples, apricots and plums in which mating disruption (MD) was not normally used. Such a large area was used to ensure that any edge effects and migration of mated OFM females would be overcome. The initial level of OFM population in 1996-97 season, before the application of the WAMD experiment was measured. During 1997-98 season the WAMD was closely monitored for OFM. More than 230 food traps for OFM monitoring were placed in the area and shoot tip and fruit damage assessments were made. Results of detail monitoring showed a reduction of OFM population in the WAMD. Also shoot tip and fruit damage in the peach blocks was reduced when surrounding pears were treated with MD compared to chemical control. The WAMD experiment showed that the OFM population was greatly reduced in the hot spots and edge effects that could be explained by migration of OFM were controlled.

Key words: mating disruption, migration, Oriental Fruit Moth, Grapholita molesta, sex pheromone, stone and pome fruit, wide area mating disruption.

 

Introduction

The one of the most important pests of commercial orchards in the Murray-Goulburn valley region of Victoria is the Oriental Fruit Moth (OFM) (Grapholita molesta Busck, Lepidoptera : Tortricidae). OFM is able to damage seriously not only peaches and nectarines as well known by Victorian growers, but also pears, apples, apricots and plums (Rice et al. 1972).

Identification of the chemical structures and synthesis of the artificial female sex pheromones has resulted in new methods of pest control based on creating artificial trails of sex pheromone which disrupt males from being able to locate unmated females, has been called mating disruption (MD). Rothschild (1975) and Vickers et al. (1985) demonstrated the possibility of the OFM control at a district-wide level in peach orchards in Victoria and NSW by MD with synthetic female pheromone. Rothschild (1979) showed that MD treatments could be as effective in controlling OFM as insecticides. Then it was suggested (Vickers et al. 1985) that MD may be more effective than insecticides, when all orchards in a district are treated, so as to reduce the likelihood of mated females migrating from untreated blocks.

Most effectively MD works in the presence of a low OFM population, as long as a sufficient amount of pheromone is assured in the environment. It is impossible to reliably estimate the population density of OFM, or to measure the amount of sex pheromone present in the volume of air within the orchard (Cravedi 1992).

Due to air movements and leaves absorption pheromone concentrations for MD in an orchard can fluctuate (Suckling and Angerilli 1996). Through the use of food traps it has been shown that mated females, albeit in small numbers, can be present even within large peach orchards where MD is applied. This situation indicates the possibility that mechanisms other than pheromone calling may lead to mating (Molinari and Cravedi 1989).

MD as a major part of Integrated Pest Management (IPM) is widely used in Australian orchards. OFM has been controlled through the use of MD for many years in Victoria. In the Murray-Goulburn valley some farmers report that shoot tip and fruit damage has more recently occurred on the border of MD peach blocks adjacent to fruit blocks where chemical control is used (Il'ichev 1997). Studies of movement of OFM have indicated that most adults do not disperse over distances greater than 200 m, although a few individuals may cover distances exceeding 1 km (Rothschild and Vickers 1991).

Our recent observations (Il'ichev et al. 1998) indicated that migration of mated OFM females from pear blocks under chemical control to adjacent peach MD blocks resulted in edge damage in peach blocks. Peach tip and fruit could attract mated females from pears, where they have developed a high population, to the adjacent peach block for oviposition. This explanation of edge effects and the occurrence of shoot tip and fruit damage mostly on borders of peach MD may also indicate a behavioural avoidance of unmated females to MD. The females may have responded to a super-abundance of their own sex pheromone by moving outside of the MD area to seek mates and then return for oviposition in response to the food attractant from shoot tip or ripening peach fruit (Il'ichev et al. 1999).

Area-wide MD program was initiated for OFM control during the 1991/92 season in 1200 ha of peaches and nectarines in the Tulbagh Valley in South Africa (Barnes and Blomefield 1996). In these experiments the MD treatment was only applied as five-row borders in all plum, prune, apricot, almond and pear orchards. By the end of the experiment, shoot tip damage was greatly reduced and not a single infested fruit was recorded from the MD treated area. This project was an outstanding success after two seasons, but later when MD applications were stopped, OFM quickly started to cause severe damage again.

After South African experiment was suggested that the success of WAMD depend on effective management of borders of MD orchards and blocks. Two factors are relevant: the decrease in the concentration of pheromone from the MD dispensers at the edges of MD blocks due to wind (Suckling and Karg 1997), and migration of mated females of OFM from non mating disruption blocks into adjacent MD areas (Barnes and Blomefield 1996a).

The WAMD experiment in Victoria has the aim to demonstrate that the OFM population will be significantly reduced with the use of MD not only in stone fruit, but also by treating every fruit tree in the region. The expectation is that this approach will be more reliable and cost effective than combining MD and chemical overspraying. The significant reduction of insecticide use will be an environmental benefit of this project. This paper reports the initial results of the first year of the WAMD application.

 

Material and methods

Description of the study area and application of WAMD

The first investigation of MD application for OFM control at a district level was carried out at Cobram in Victoria in 1985 (Vickers et al. 1985). This particular area was chosen because most of the growers in it have had experience in managing MD. Also some background information on OFM distribution in this area was available from earlier trials. Some growers had applied MD in peach blocks for more than 10 years and successfully controlled OFM population. Particularly in this region in recent years, growers have reported an increase in damage to shoot tip and fruit caused by OFM. The most severe damage was typically found at the edge of peach blocks under MD, adjacent to pear blocks under chemical control. The idea to treat all orchards in a district with MD would be expected to help reduce the likelihood of mated OFM females migrating between fruit blocks and orchards and thus improve the effectiveness of MD in the whole area.

The Wide Area Mating Disruption (WAMD) experiment was conducted in over 800 hectares on 18 different orchards in the Cobram region in Northern Victoria during the 1997-98 season. The area included 550 hectares of peaches and nectarines, which had been treated with MD in previous seasons. The balance of the WAMD included pears and apples, plums and apricots that had not been treated with MD previously.

The entire experimental area was saturated with OFM pheromone by treating every fruit tree at the recommended rate of 4 lures of "Isomate OFM Plus" per tree. This included pears, apples, apricots and plums in which mating disruption was not normally used. The whole area was considered to be extensive enough to ensure that, within it, any edge effects and OFM migration problems would be overcome.

During the 1996-97 season two areas were designated as hot spots according to the monitoring data. In these areas, shoot tip and fruit damage was high and more than 50 males or more than 10 OFM were caught per week in pheromone or food traps respectively. Three control sites without MD treatment were identified. Two were separate orchards, adjacent to the north and south borders of the WAMD and one was a block of pears under the chemical control opposite to peaches under MD within the WAMD.

The WAMD experiment was continued in 1998-99 season in expanded area over 1,100 hectares on 40 different orchards in the same region. The preliminary results shown the effectiveness of WAMD approach in the beginning of the season when the initial level of OFM population was low in whole area.

Monitoring the OFM population in WAMD and investigation of hot spots

The WAMD was closely monitored for OFM throughout the season with food traps. The Efecto-fly traps (Efecto-fly trap, Avond Pty. Ltd.,W.A.), 1/3 filled in with 10% brown sugar solution and 12 drops of terpinyl acetate, were used as a food traps to indicate the level of OFM population in MD blocks. Such food traps are not specific for OFM, but are able to attract males and females of OFM in orchards under MD. The food traps were monitored weekly by collecting OFM and changing the sugar and terpinyl acetate solution.

More than 230 food traps for OFM monitoring and mapping of the hot spots of OFM population have been placed in the WAMD. At least one food trap was placed in all blocks of each fruit variety inside each orchard that was part of the WAMD. Additional traps were put into blocks larger than 3 ha and overall the average trap density was one trap in 3-5 ha.

There were two main hot spots found in two properties within the WAMD in the 1996-97 season. Twenty one food traps were placed in each hot spot in property 1 and 2. Hot spots were monitored with a trap distribution of 7 traps in 3 lines through the interface of pears and peaches. Two replications were used with the same distance of 5 trees in between traps. The weekly monitoring of the WAMD experiment started on August 21, 1997 before the start of the first overwinter flight of OFM and was continued until two weeks after the last OFM flight finished.

Shoot tip damage assessment

The OFM larvae damage actively growing shoot tips of peach tree. After hatching the larvae enter twigs, usually near the tip, and tunnel into the shoot for 8-10 cm. This causes the tip to die or wilt. Also larvae can attack the developing peach and pear fruits.

Two shoot tip damage assessments (16.12.97 and 21.1.98) were carried out only in property 1, as property 2 had no visible tip damage. Fifty tips were counted from each peach tree of the 3 rows where food traps were placed in the hot spot and 3 rows in the control. From east and west side of the tree canopy 25 tips were counted randomly. All damaged tips were recorded and the percentage of damaged tips was calculated.

Management and analysis of data

A geographic information system (GIS) was used for the management, visualisation and analysis of the monitoring and damage assessment data from the WAMD experiment. GIS is a system of computer hardware, software, and geographic data, designed to efficiently capture, store, update, analyse and display all forms of geographically referenced data. The location of orchard blocks and traps were entered into the GIS using sketch maps of each property in conjunction with satellite imagery and digital cadastral information for the WAMD. Each digitised orchard property was given a unique identifier, as was each trap. To enable useable comparisons to be made between the traps counts, the number of OFM caught per trap were tabulated for weekly time periods. Once all of the monitoring and damage assessment data had been entered, a desktop GIS package (ArcView 3.0a®) was used to locate and interpret the data with respect to other datasets from the ISIA GIS data library such as cadastre of the Cobram area and the road network. The zooming functionality of ArcView 3.0a® enabled the mapping scale of the data to be easily manipulated, and could range from the entire study area to individual orchards or to the detail of individual traps, depending on the viewer's interest.

 

Results and discussion

Monitoring the OFM population in WAMD and investigation of hot spots

Monitoring data of 1997-98 season from the food traps placed on 18 properties under WAMD confirmed two distinct hot spots of OFM in properties 1 and 2. These hot spots had been known from the 1996-97 season, when MD was applied only on peaches and severe damage occurred on the edges of MD peach blocks. Under WAMD the OFM population greatly reduced in one hot spot (property 2) in 1997-98 season and the population continued to be low till December 1998. The level of OFM population during the first overwinter generation in property 2 was approximately half compare to that in property 1. In subsequent generations the OFM number became insignificant in property 2 and there was no visible shoot tip and fruit damage in this property. This indicates that WAMD was able to control the hot spot with a medium level of OFM population (5-10 moth per week per trap) (Fig. 1).

Figure 1. Monitoring of OFM population in WAMD.

The results from the other hot spot, where the OFM population was higher with more then 20 moths per week per trap during first overwinter generation is shown in Fig. 2. In 1997/98 the number dropped greatly during the second generation and did not show any sharp increase up to the end of the season although the numbers continued at a dangerous level. In 1996/97 this drop showed during the third generation and the number increased again during the last generation. The initial overwinter population was identical in both seasons (Fig. 2). The result indicated that the WAMD was successfully reduced the OFM number even in the second hot spot where the population level was high. Within WAMD area OFM number was low, below damage level (0-5 per week per trap), but in hot spots it was between 5-20 OFM per week per trap.

The results of 1997/98 also support that OFM can concentrate in pear blocks under chemical control and may provide a reservoir for further infestation of adjacent peaches under MD. The population declined steadily when the adjacent pear block was under MD but OFM remained constant when the pear block was under chemical control. In both example the initial overwinter population was comparable (Fig. 3).

Shoot tip damage in peaches under MD in property 1 indicated that mated females from the flight of the overwinter generation oviposited mostly on the border trees especially in the peach MD block opposite to pear chemical. Percentage of tip damage was also higher on the first three trees in the peach MD block opposite to pear MD, but the percentage of damage was almost half compare to that of other block (Fig. 4).

Figure 2. Comparison of OFM catch in food traps (property 1).

Shoot tip damage assessment

The results of damage assessment from shoot tip as well as from food trap catches confirmed the higher level of infestation of OFM in the border of peach MD blocks next to the pear blocks under chemical control after the overwinter generation.

Fig. 5 indicated that percentage of shoot tip damage reduced throughout the block in 1997/98 compare to that of 1996/97, damaged tips were almost zero during 1998/99 season in the same property. This also indicates that WAMD was able to reduce shoot tip damage, even in hot spots with high number of OFM. The hot spot with the intermediate initial level of OFM was controlled after 1 year of WAMD. The more intense hot spot was controlled in the second year of WAMD when shoot tip and fruit damage was greatly reduced. This indicates that WAMD approach worked effectively.

Figure 3. OFM monitoring with Food Traps in Property 1 (Peaches MD).

Figure 4. Tip Damage Assessment in Propery 1 (16.12.97) The data shows average tip damage from 3 lines of peach trees. Tree No 1 is at the pear-peach interface.

Figure 5. The data shows average tip damage from 3 lines of peach trees (Property 1).

 

Acknowledgments

The project was funded by the Horticultural Research and Development Corporation, Canned Fruits Industry Council of Australia, Victorian Peach and Apricot Growers Association, Cobram Fruitgrowers Association, Biocontrol Pty. Ltd., I.K. Caldwell Pty. Ltd., and the Cobram fruit growers involved in the Wide Area Mating Disruption.

We would like to thank the assistance of Mr. Russell Fox and Mr. Peter Spencer from I.K. Caldwell for monitoring, Mr. Mike Morris and Ms. Heyley Rokahr for their input to the GIS aspects of the WAMD experiment.

 

References

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Barnes, B.N. & Blomefield, T.L. 1996a: Mating disruption manual for Codling Moth and Oriental Fruit Moth. Infruitec, Stellenbosch: 37.

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