Application date	Boll damage (%)
	Second half of July	First half of August
May 14	1.7	2.3
May 18	2.8	2.5
May 30	8.0	11.3
June 10	13.3	28.0

Table 2 Active ingredients used for mating disruption in relation to female sex pheromones

Species	Compounda	Composition of		Disruptant
		Attractant (%) a	Disruptant (%)
Pectinophora gossypiella	Z7,Z11-16Ac	50	50	Pheromone
	Z7,E11-16Ac	50	50
Carposina niponensis	Z7-20-11Kt	95	100	Main component
	Z7-19-11Kt	5	0
Adoxophyes  spec.	Z9-14Ac	61
	Z11-14Ac	31	100	Minor component
	E11-14Ac	4
	10me-12Ac	2
Epiphyas postvittana	E11-14Ac	95	66	Off-blend
	E9,E11-14Ac	5	5
	Z11-14Ac	-	29
a see Arn et al. (1992, 1996)

Release rates and dispenser life

Zero order release rate is a very important characteristic of pheromone dispensers. Many dispensers have a rather high release rate in the beginning, which gradually decreases within a few weeks (Figure 2). Isomate-C dispensers contain a 60:30:1-blend of (E,E)-8,10-dodecadienol (E8,E10-12OH; codlemone), dodecanol (12OH) and tetradecanol (14OH) at 203 mg/dispenser. These dispensers still contain 75 mg after 140 days and will continue to be effective for another 30 days.

Figure 2 Release rates of three dispensers for mating disruption of codling moth, C. pomonella (Gut et al. pers. comm.; Washington State University)

In order to allow for a too rapid decrease in release rates, a split application is recommended for pink bollworm, P. gossypiella, in Egypt; some dispenser types should be applied two or three times, at short intervals. However, this is not a satisfactory approach. Efforts should therefore be made to develop a zero order release system, which is almost achieved by PB-rope dispensers (Figure 3).

Figure 3 Split application of dispensers recommended against pink bollworm, P. gossypiella, in Egypt

Quite obviously, a temperature-independent release system would be preferable, as currently available dispensers release high amounts of pheromone uselessly during daytime. We measured aerial concentrations in a pheromone-treated field and found that the pheromone concentrations are almost constant, regardless of different release rates at different temperatures. It seems that strong convection flows carry the pheromone upwards into the sky at high temperatures (during daytime; in summer).

Another, most important factor is wind velocity (Tables 3, 4). An ideal dispenser should release pheromone proportional to wind velocity at low wind speeds; but should release less at strong winds, when no mating activity occurs. A dangerous situation arises from decreased release rates after periods of continuously strong winds (Figure 4).

Dispenser life is obviously a most important property. Short-life dispensers cannot absorb the change of climatic conditions, they are much less reliable at hot temperatures. There is also the problem to properly time the next application.

Stability of active ingredient

Aldehyde pheromones are easily oxidized to acids. Therefore, antioxidants and UV-adsorbers are usually added to the active ingredient, as well as to the polymers in the dispenser wall.

Pheromones also polymerize to form oligomers. Aldehydes easily form trimers. Isomerization is quite common in compounds with conjugated double bonds. Stabilizers and UV adsorbers are added to protect the compounds against these reactions.

Under certain conditions, acetates are hydrolyzed to the alcohol and acetic acid by fungi (Table 5).

Others

The development of a degradable dispenser is desirable. Sprayable dispensers would be much better than existing dispensers, but it is very difficult to develop long-life sprayable dispensers.

Area-wide application
[top]

Area-wide application of mating disruption is recommended for a number of reasons. One is that a comparatively higher pheromone dose is required for small fields, and that the cost of mating disruption is therefore not competitive with insecticide treatments. A rough estimation is that a ten times larger field requires only half the pheromone dosage/ha, compared to a small field. Population control of pink bollworm at late season tends to be much more efficient in larger areas, which results in a smaller first generation the next year, thus further increasing the efficacy of pheromone treatments (Tables 6, 7; Figure 5).

In larger treatments, the effect of immigrating gravid females is less critical and populations of natural enemies are expected to be higher.

Natural enemies
[top]

Mating disruption is usually designed to control one target species. Other minor pests are in part effectively controlled by their natural enemies, which benefit from the reduction of pesticide treatments. However, after insecticide sprays, the efficacy of pheromone treatment, also with respect to the target pest, is decreasing. And other species become more virulent and must be treated with additional pheromone compounds or insecticide sprays (Table 8).

The use of insecticide sprays is known to induce serious secondary pests. One well-known example are gradations of mites as a result of pyrethroid sprays. Insecticides are not always efficient to control even the target species, due the induction of insecticide-resistant strains and their negative effect on beneficials (Table 9).

Control threshold
[top]

The threshold of economically tolerable damage is a very important factor. In Japan, New Zealand and South Africa, the threshold of apple pests is 0.1% or lower, while it is between 1 and 2% in other countries. At extremely low population densities, the natural enemies are not blessed with enough food and their activity, therefore, remains low.

At extremely high pest population densities, on the other hand, mating disruption is often not effective and curative insecticide sprays must be applied initially.

Conclusion

We have much confidence in the efficacy of the mating disruption technique, if good dispensers releasing sufficient amounts of the proper active ingredients are applied at an early stage in area-wide control systems, in the presence of natural enemies.

References

Arn H, Tóth M, Priesner E (1992) List of sex pheromones of Lepidoptera and related attractants, 2nd edition. Montfavet: International Organization for Biological Control

Arn H, Tóth M, Priesner E (1996) The pherolist. Internet edition: http://www.nysaes.cornell.edu/pheronet

[top]