Mating disruption of codling moth, Cydia pomonella L.: Experiences from the U.N.C.A.A. Arbotech Pool

Pierre Becid

• Introduction
• Materials and methods
• Results
• Conclusions
• Reference

Key words - sex pheromone, mating disruption, technology transfer, integrated pest control, apple, pome fruit, codling moth, Cydia pomonella

Introduction
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Despite a growing use of insecticides, the damage caused by codling moth in Provençal apple orchards has steadily increased from 1990 to 1993. Since then, difficulties to control this pest have been encountered in all other regions. Crop damage has now exceeded the 2% threshold in, for example, more than 20% of the orchards in the Garonne valley and in 15% of the orchards in the Loire valley.

Laboratory studies have confirmed the development of resistance and cross-resistance of codling moth to all insecticides used for conventional control. Fortunately, resistant strains are yet not widely spread in the field. Besides, there may be important differences in the sensitivity of codling moth to the various active ingredients, even within each chemical family. However, some insecticide failures have been all too hastily attributed to assumed resistances, while the real causes are quite often related to non-compliance to prophylactic measures, "holes" in the treatment calendar, lack of protection against the first generation or poorly regulated spraying.

Confronted with the growing importance of codling moth, fruit growing is placed in a fragile state of equilibrium. Control programs must be understood as a function of orchard characteristics and history, and they should involve strategies for the prevention of resistance by maintaining the use of a range of chemicals. The Arbotech Pool cooperatives have therefore directed their efforts not only to the research and development of insecticides, but also to a prospective assessment of the mating disruption technique. At present, mating disruption products for codling moth are not registrated in France.

Materials and methods
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Four mating disruption trials were carried out by three cooperatives within the U.N.C.A.A. Arbotech Pool: by C.A.P.L. at Vignères, by Alpesud at Laragne, and by Union Set at Saint Aubin and at La Bourdaisière Chenu.

At least two orchards of 2 to 2.5 ha were treated at each site; one with insecticides and one with Ecopom dispensers (Isagro, Novara, Italy). The Ecopom dispenser is a resin-treated cellulose pad, loaded with 250 ± 25 mg (E,E)-8,10-dodecadien-1-ol (E8,E10-12OH, codlemone) (Rama 1997).

The dispensers were applied twice per season, at 300 dispensers/ha inside the orchard, and at 400 dispensers/ha along the border. During the trial at La Bourdaisière Chenu, an insecticide treatment against the first generation was combined with a single dispenser application against the second generation.

The trials were monitored by codlemone-baited traps; dispenser life and release rates were estimated according to degree-days. In each orchard, 1 000 apples were checked for visible damage. The controls were done on a daily basis, extending from the first occurrence of second-instar larvae until harvest.

Results
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The trials carried out at Vignères (Vaucluse) and Saint Aubin/La Bourdaisière Chenu (Loire valley), under completely different climatic conditions, clearly demonstrate the efficacy of the mating disruption technique.

At Vignères, two pheromone-treated orchards showed a very low rate of fruit attack (0.5 and 0.3%, respectively), which was equivalent to the insecticide-treated control (0.4%; Table). It should be noted that the amount of insecticide applied in the control orchard was quite typical for the Provence region: 17 specific anti-codling moth sprays, including 9 with organophosphates.

Table  Mating disruption (MD) of codling moth, C. pomonella, in four different locations in France (1995)

	C.A.P.L.a		Alpesudb		Union Setc		Union Setd
	Control	MD	Control	MD	Control	MD	Control	MD
Dispenser application	-	May 5	-	May 15	-	May 3	-	-
	-	July 5	-	July 21	-	July 7	-	Aug. 1
No. insecticide treatments	17	0	3	0	5	0	7	5
Fruit attack (%)
1st generation	0	0	0	0.7	0	0	0.5	0.5
2ndgeneration	0.4	0.2	5	7.1	0	0	-	-
At harvest	0.4	0.4	16.3	13.4	4.6	0.6	5.1	0.7

^a Vignères, Provence; ^b Laragne, Hautes Alpes; ^c Saint Aubin, Loire valley; ^d La Bourdaisière Chenu, Loire valley; ^e Insecticide treatment against first generation

In the Loire Valley, the Union Set trial (Table) showed a 0.6% fruit damage in the mating disruption orchard, while insecticide control in the reference orchard was not satisfactory. This orchard was sprayed only 5 times, resulting in an insufficient control at high population levels.

The trial carried out at Laragne by Alpesud (Table) has two points of interest. First of all, it illustrates that mating disruption is not reliable at high population densities. Monitoring traps showed unusually high catches at the onset of the first flight (Figure), probably due to immigration from a nearby abandoned pear orchard.

Figure Attraction of codling moths, C. pomonella, to monitoring traps at Laragne (1995)

It also shows that even insecticide treatments fail, if not applied properly. The farmer obviously underestimated the codling moth risk and sprayed only three times. In addition, one of the products was erroneously underdosed at one-tenth. It should be added that visual controls were not carried out often enough to detect the high level of infestation.

This test demonstrates that both insecticide treatments and mating disruption are not infallible techniques. Critical conditions, such as high population densities or immigration of moths, have to be taken into account and methods must be made available to predict these.

The efficacy of mating disruption was found to be excellent in the Union Set trials carried out at Saint Aubin and La Bourdaisière Chenu, where the first generation was treated with insecticides and the second by the application of dispensers (Table). The combined use of conventional methods and mating disruption may prove to be a future strategy to ensure better control of the codling moth.

Conclusions
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Mating disruption is, when properly used, a promising method for the management of codling moth populations. The Arbotech Pool is continuing experimental work in 1996 in order to specify the dispenser life as a function of temperature and to integrate mating disruption into the framework of an overall pest control strategy.

However, it is necessary to emphasize that mating disruption against codling moth is still in the experimental stage. This technique may in no case be thought of as an ordinary plant protection product; training is required to ensure its appropriate use.

And, the mating disruption technique is not a universal cure-all. It will hopefully soon be made available to the farmer, but it will have to be integrated within an overall treatment strategy. This obviously complies with the concept pioneered by the fruit farmers themselves: la lutte integrée.

Reference

Rama F (1997) Ecopom dispensers for mating disruption in apple orchards (This volume)

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