CorrectMyText Users
English language
The text to correct from user stephy
Major volatile semiochemicals being extremely unstable due to their chemical structure, it is necessary to formulate them so that they are protected from degradation by UV light and oxygen. Moreover, the formulation must ensure a controlled release of semiochemicals. To be efficient in IPM strategies, semiochemical slow-release devices must have specifications: the dose released must be sufficient to be detected by insects; the rate of release must ideally be constant and correspond to a zero-order kinetic; the release of semiochemical must be ensured during all the period of insect occurrence. Furthermore, production of such devices must be reproducible. However, in practice, it is sometimes difficult to develop such devices in respect with all the previous described criteria. Indeed, environmental factors play an important role in the release kinetic of volatile semiochemicals. This point will be developed in the next chapters.
Several formulations and devices have been developed and commercialized with various slow-release capacities. Some examples of dispensers are described hereafter. The majority of them involve mating disruption of moth. Three groups can be distinguished: solid matrix dispensers, liquid formulations to spray and reservoirs of formulations. On an historical point of view, the first related and the most commonly used pheromone dispenser is the natural rubber septum (Roelofs et al. , 1972). Table 1 relates some examples of pheromone dispensers and formulations with specific characteristics.
Solid matrix dispensers are manually applied on crops or in orchards. The semiochemicals are incorporated in a solid matrix. Because of the various materials that can be used to constitute a matrix (see below for material presentation), the release rates for a single molecule, can differ significantly from one device to another, as demonstrated by Golub et al. (1983) for the measurement of release rate of gossyplure ((Z, Z) - and (E, Z) -7, 11-hexadecadien-1-yl acetate), the sex pheromone blend of the pink bollworm (Pectinophora gossypiella Saunders, Lepidoptera: Gelechiidae) from different formulations (see Table 1).
The most common solid matrix used in dispensers are polyethylene tubes (twist tie dispensers like Isomate®), polyethylene sachets (Torr et al. , 1997), polyethylene vials (Johansson et al. , 2001; Zhang et al. , 2008), membrane dispensers (CheckMate CM-XL®), spiral polymer dispensers (NoMate CM®) (Tomaszewska et al. , 2005), polymer films, rubber septa (McDonough, 1991; Möttus et al. , 1997), rubber wicks, polyvinyl chloride (PVC), hollow fibers (Golub et al. , 1983), impregnated ropes, wax formulations, gel-like dispensers matrices (Atterholt et al. , 1999).
Drawbacks encountered with solid matrix dispensers include the difficulty to maintain a zero-order release kinetic (constant release rate) during a long period of time, and the decreasing of semiochemical concentration in the air with the distance from the dispenser. Consequently, these dispensers are only efficient to attract and trap insects at short distance. A way to by-pass this problem is to apply devices in sufficient points in the crop or in the orchard. The resulting disadvantage is the high manpower needed to implement devices by hand in the fields. Another shortcoming is the non biodegradability of the formulated polymers (Stipanovic et al. , 2004).
The effective lifetime of the biggest solid matrix dispensers can range from 60 to 140 days. Consequently, a single application at the first apparition of the pest can be sufficient to ensure crop protection.
Sprayable slow-release formulations are generally composed of a biodegradable liquid matrix compound in which the semiochemical is dissolved. Regularly, other components can be added to protect the semiochemicals, like UV-stabilizers, antioxidants (vitamine E for e. g. ) and surfactants. Very often, the sprayable formulation consists in a microemulsion, resulting in polymeric microbeads containing the semiochemicals (microencapsulated pheromones) dispersed in a liquid matrix (de Vlieger, 2001). In 1999, Atterholt et al. studied the release rates of oriental fruit moth sexual pheromones formulated in aqueous paraffin emulsions as carrier material.
The time of efficiency of such formulations ranges from days to weeks depending on environmental factors, microbead size and release capacities, and the pheromones chemical properties (Welter et al. , 2005).
The major advantage of sprayable formulations compared to solid matrix dispensers is that the whole crop can be treated.
Reservoirs generally consist in two parts, a reservoir and a diffusion area. Hofmeyr et al. (1995) described a dispenser consisting in glass tube acting as a pheromone-impermeability reservoir attached to a short polyethylene tubing through which the pheromone can diffuse. Another reservoir was tested by Shem et al. (2009) as repellent allomone device against tsetse flies. The upper part (reservoir) was made of aluminum and the diffusion area was made from Tygon® silicon tubing.
An electronic device (Suttera® puffer for e. g. ) which consists in a big electronically programmed reservoir of formulation, allows high emission of pheromone by means of a pressurized aerosol. Puffs can be emitted at fixed time intervals. The advantage of this system is the use of fewer dispensers per area to treat.
4. 2. Slow release rate studies
Many dispensers commercialized for practical applications do not guarantee a release at a steady rate, inducing a decrease of release rate over time. The best method to approach the zero-order kinetic of release rate is to use semiochemical reservoir systems (Atterholt et al. , 1999). However, the most important is to know at which moment the quantity of semiochemical released is under the minimum required dose to act on the insect behaviour and to change the dispenser. Moreover, it is also known that the release rate is influenced by environmental factors such as temperature and wind which can induce important fluctuations of release rate in a short period of time.
4. 2. 1. Techniques to estimate release rates
Since it is not easy and reliable to measure release rates directly in the field, the techniques for estimating release rates of semiochemicals from various formulations were developed in laboratory or semi-controlled conditions using three different methods which were improved over time: the gravimetric method, the total organic solvent extraction, and the dynamic collection of volatiles. The first technique, less and less used, consists in weighing dispensers at daily intervals over the season and to determine the percentage of mass loss over time. The major shortcoming of this technique is the lack of precision and accuracy to establish release rates. Sometimes, the mass increases instead of decreasing due to the presence of humidity and dust deposited on the dispensers.
The second technique implies the total organic solvent extraction of semiochemicals from dispensers to determine the residual concentration of compound in field-aged devices. The condition to have an optimal pheromone extraction is that the organic solvent must completely dissolve the compound contained in the dispenser (Lopez et al. , 1991; Möttus et al. , 1997). This technique has the advantage to permit to qualify and quantify the pheromone and its potential volatile degradation products by gas chromatography (GC) analysis. However, it presents a risk of not permitting detection of non volatile degradation products by GC (Tomaszewska et al. , 2005).
The third method to determine release rate consists in a dynamic sampling and an adsorbent trapping of volatile compounds from field-aged dispensers. The evolution of release rate is estimated as a function of field-aging of devices. It is important to measure the rate every time in the same conditions of atmospheric pressure, temperature, relative humidity and air flow to have comparable analysis over time. The volatile collection system is generally composed of a chamber in which air flows through the dispenser. The carried volatile semiochemicals are trapped on an adsorbent cartridge, followed by solvent extraction or thermal desorption and GC analysis. Various adsorbents have been tested like Super Q (Mayer et al. , 1998; Atterholt et al. , 1999; Meagher, 2002), silica gel (McDonough et al. , 1992; Pop et al. , 1993), Tenax (Cross, 1980), Carbograph, Porapak Q (Cross et al. , 1980), activated charcoal, polyurethane foam (PUF) (Van der Kraan et al. , 1990; Tomaszewska et al. , 2005). The choice of the adsorbent depends on the physic-chemical properties of the semiochemicals to trap, and on the air output which could be applied on the cartridge with the minimum air resistance and without breakthrough of the semiochemical compounds.
Considering the advantages and shortcomings of the three techniques, the last one is the more appropriate and accurate in order to estimate release rate of semiochemicals from dispensers.
4. 2. 2. Release rates studies
The release of volatile semiochemicals in the atmosphere is dependent on two major factors: the diffusion speed of the compound through the dispenser matrix and the evaporation speed of the molecule in the air (Krüger et al. , 2002). The first factor depends on the characteristics of the dispenser (type of matrix, shape, thickness, distribution of the semiochemical in the matrix) while the second factor (speed of evaporation) mainly depends on environmental parameters like air temperature, wind speed, relative humidity and the physical properties of the compound itself. (Alfaro-Cid et al. , 2009; http: //www. cbceurope. it/images/stories/file/biocontrol/GuidaBioENG. pdf). In case the evaporation process of pheromone from the surface of dispenser is slower than the diffusion step, the speed of evaporation is the limiting factor, and the first-order release kinetic equation is considered:
C0 = Ct e-kt,
where C0 is the amount of compound in the dispenser at the beginning of evaporation, Ct is the amount of compound at time t, and k is the evaporation rate constant. In case of a first-order kinetic, a half of the amount of the pheromonal compound will be evaporated after a time t1/2, called half-life of the compound (McDonough et al. , 1989; Möttus et al. , 2001).
Many studies were conducted to give an estimation of the release rate of pheromone over time from dispensers in specific experimental conditions. However, very few studies developed rate kinetic predictive models in function of physic-chemical features (temperature, relative humidity, wind speed…). Moreover, these experiments only considered one parameter at a time instead of treating the combined parameters in an experimental design to finally obtain a realistic modelization of release rate, close to the rate expected on the field. McDounough et al. (1992) described a modelization of pheromone release rate by determining the half-life times of dispensers in fixed conditions. Most recently, Alfaro-Cid et al. (2009) attempted to develop a pheromone dispenser (sex pheromone of codling moth, Cydia pomonella L. (Lepidoptera: Olethreutidae)) less sensitive to climatic conditions by modeling a relationship between rate and on-field measured temperature and humidity.
The results of some studies on release rate estimation or modelisation are summarized in Table 1. Some of them are described in more details hereafter:
Shem et al. (2009) studied the influence of temperature on the release rate of a blend of allomones derived from waterbuck odor, in a reservoir type dispenser, to control tsetse flies. As expected, the release rate increases in function of the temperature. The same was demonstrated by Atterholt et al. (1999) considering the release of oriental fruit moth pheromone from paraffin emulsions at three temperatures from 27°C to 49°C. It is noticeable that at the lower temperature, the release rate was constant over time (during 100 days). The release rate was higher at 38°C and 49°C but the difference between these two temperatures was little. However, the release rate decreased with time at higher temperatures due to pheromone oxidation and degradation phenomena.
Van der Kraan et al. (1990) determined the influence of temperature and air velocity on various types of dispensers releasing moth sex pheromones. The conclusions of this study were that the influence of temperature is more important than wind speed on the release rate. Nevertheless, the effect of air movement in natural environmental conditions could not be underestimated.
Many other studies were led in a goal to attempt a mathematical model of release rate in function of physic-chemical parameters. It is clear that the most influencing environmental parameter is temperature which modifies the speed of evaporation of volatile semiochemical compounds. However, for this factor and for the others (wind speed, relative humidity, UV light, oxygen), the influence on release rate is depending on the design of dispenser (shape, polymeric matrix, thickness…) and the semiochemical compound itself.
5. Conclusions
The determination of the evolution of slow-release rate as a function of environmental conditions, considering the influence of temperature, wind speed, relative humidity, sunlight, has to be processed case by case. Indeed, in practice, it is not possible to obtain a global mathematical model for all dispensers and compounds. Experiments conducted to approach the environmental conditions faced the constraint that the fluctuations observed in field are too unpredictable and random to be reproduced in laboratory. The laboratory studies can only predict limitations of use in fixed conditions and give theoretical information on longevity of lures.
The best way to estimate the release-rate efficiency is to regularly analyze field-aged dispensers in order to determine if the lower threshold limit of rate is attained. Ideally, theoretical modelization could be based on experimental designs (Box-Behnken design for e. g) taking into account the combination of various physico-chemical data.
In conclusion, the use of semiochemical slow-release devices to control pests requires the knowledge of numerous scientific fields going from the entomology to the technical implementation of dispensers.
Language: English
Language Skills: Native speaker, Proficiency
Several formulations and devices have been developed and commercialized with various slow-release capacities. Some examples of dispensers are described hereafter. The majority of them involve mating disruption of moth. Three groups can be distinguished: solid matrix dispensers, liquid formulations to spray and reservoirs of formulations. On an historical point of view, the first related and the most commonly used pheromone dispenser is the natural rubber septum (Roelofs et al. , 1972). Table 1 relates some examples of pheromone dispensers and formulations with specific characteristics.
Solid matrix dispensers are manually applied on crops or in orchards. The semiochemicals are incorporated in a solid matrix. Because of the various materials that can be used to constitute a matrix (see below for material presentation), the release rates for a single molecule, can differ significantly from one device to another, as demonstrated by Golub et al. (1983) for the measurement of release rate of gossyplure ((Z, Z) - and (E, Z) -7, 11-hexadecadien-1-yl acetate), the sex pheromone blend of the pink bollworm (Pectinophora gossypiella Saunders, Lepidoptera: Gelechiidae) from different formulations (see Table 1).
The most common solid matrix used in dispensers are polyethylene tubes (twist tie dispensers like Isomate®), polyethylene sachets (Torr et al. , 1997), polyethylene vials (Johansson et al. , 2001; Zhang et al. , 2008), membrane dispensers (CheckMate CM-XL®), spiral polymer dispensers (NoMate CM®) (Tomaszewska et al. , 2005), polymer films, rubber septa (McDonough, 1991; Möttus et al. , 1997), rubber wicks, polyvinyl chloride (PVC), hollow fibers (Golub et al. , 1983), impregnated ropes, wax formulations, gel-like dispensers matrices (Atterholt et al. , 1999).
Drawbacks encountered with solid matrix dispensers include the difficulty to maintain a zero-order release kinetic (constant release rate) during a long period of time, and the decreasing of semiochemical concentration in the air with the distance from the dispenser. Consequently, these dispensers are only efficient to attract and trap insects at short distance. A way to by-pass this problem is to apply devices in sufficient points in the crop or in the orchard. The resulting disadvantage is the high manpower needed to implement devices by hand in the fields. Another shortcoming is the non biodegradability of the formulated polymers (Stipanovic et al. , 2004).
The effective lifetime of the biggest solid matrix dispensers can range from 60 to 140 days. Consequently, a single application at the first apparition of the pest can be sufficient to ensure crop protection.
Sprayable slow-release formulations are generally composed of a biodegradable liquid matrix compound in which the semiochemical is dissolved. Regularly, other components can be added to protect the semiochemicals, like UV-stabilizers, antioxidants (vitamine E for e. g. ) and surfactants. Very often, the sprayable formulation consists in a microemulsion, resulting in polymeric microbeads containing the semiochemicals (microencapsulated pheromones) dispersed in a liquid matrix (de Vlieger, 2001). In 1999, Atterholt et al. studied the release rates of oriental fruit moth sexual pheromones formulated in aqueous paraffin emulsions as carrier material.
The time of efficiency of such formulations ranges from days to weeks depending on environmental factors, microbead size and release capacities, and the pheromones chemical properties (Welter et al. , 2005).
The major advantage of sprayable formulations compared to solid matrix dispensers is that the whole crop can be treated.
Reservoirs generally consist in two parts, a reservoir and a diffusion area. Hofmeyr et al. (1995) described a dispenser consisting in glass tube acting as a pheromone-impermeability reservoir attached to a short polyethylene tubing through which the pheromone can diffuse. Another reservoir was tested by Shem et al. (2009) as repellent allomone device against tsetse flies. The upper part (reservoir) was made of aluminum and the diffusion area was made from Tygon® silicon tubing.
An electronic device (Suttera® puffer for e. g. ) which consists in a big electronically programmed reservoir of formulation, allows high emission of pheromone by means of a pressurized aerosol. Puffs can be emitted at fixed time intervals. The advantage of this system is the use of fewer dispensers per area to treat.
4. 2. Slow release rate studies
Many dispensers commercialized for practical applications do not guarantee a release at a steady rate, inducing a decrease of release rate over time. The best method to approach the zero-order kinetic of release rate is to use semiochemical reservoir systems (Atterholt et al. , 1999). However, the most important is to know at which moment the quantity of semiochemical released is under the minimum required dose to act on the insect behaviour and to change the dispenser. Moreover, it is also known that the release rate is influenced by environmental factors such as temperature and wind which can induce important fluctuations of release rate in a short period of time.
4. 2. 1. Techniques to estimate release rates
Since it is not easy and reliable to measure release rates directly in the field, the techniques for estimating release rates of semiochemicals from various formulations were developed in laboratory or semi-controlled conditions using three different methods which were improved over time: the gravimetric method, the total organic solvent extraction, and the dynamic collection of volatiles. The first technique, less and less used, consists in weighing dispensers at daily intervals over the season and to determine the percentage of mass loss over time. The major shortcoming of this technique is the lack of precision and accuracy to establish release rates. Sometimes, the mass increases instead of decreasing due to the presence of humidity and dust deposited on the dispensers.
The second technique implies the total organic solvent extraction of semiochemicals from dispensers to determine the residual concentration of compound in field-aged devices. The condition to have an optimal pheromone extraction is that the organic solvent must completely dissolve the compound contained in the dispenser (Lopez et al. , 1991; Möttus et al. , 1997). This technique has the advantage to permit to qualify and quantify the pheromone and its potential volatile degradation products by gas chromatography (GC) analysis. However, it presents a risk of not permitting detection of non volatile degradation products by GC (Tomaszewska et al. , 2005).
The third method to determine release rate consists in a dynamic sampling and an adsorbent trapping of volatile compounds from field-aged dispensers. The evolution of release rate is estimated as a function of field-aging of devices. It is important to measure the rate every time in the same conditions of atmospheric pressure, temperature, relative humidity and air flow to have comparable analysis over time. The volatile collection system is generally composed of a chamber in which air flows through the dispenser. The carried volatile semiochemicals are trapped on an adsorbent cartridge, followed by solvent extraction or thermal desorption and GC analysis. Various adsorbents have been tested like Super Q (Mayer et al. , 1998; Atterholt et al. , 1999; Meagher, 2002), silica gel (McDonough et al. , 1992; Pop et al. , 1993), Tenax (Cross, 1980), Carbograph, Porapak Q (Cross et al. , 1980), activated charcoal, polyurethane foam (PUF) (Van der Kraan et al. , 1990; Tomaszewska et al. , 2005). The choice of the adsorbent depends on the physic-chemical properties of the semiochemicals to trap, and on the air output which could be applied on the cartridge with the minimum air resistance and without breakthrough of the semiochemical compounds.
Considering the advantages and shortcomings of the three techniques, the last one is the more appropriate and accurate in order to estimate release rate of semiochemicals from dispensers.
4. 2. 2. Release rates studies
The release of volatile semiochemicals in the atmosphere is dependent on two major factors: the diffusion speed of the compound through the dispenser matrix and the evaporation speed of the molecule in the air (Krüger et al. , 2002). The first factor depends on the characteristics of the dispenser (type of matrix, shape, thickness, distribution of the semiochemical in the matrix) while the second factor (speed of evaporation) mainly depends on environmental parameters like air temperature, wind speed, relative humidity and the physical properties of the compound itself. (Alfaro-Cid et al. , 2009; http: //www. cbceurope. it/images/stories/file/biocontrol/GuidaBioENG. pdf). In case the evaporation process of pheromone from the surface of dispenser is slower than the diffusion step, the speed of evaporation is the limiting factor, and the first-order release kinetic equation is considered:
C0 = Ct e-kt,
where C0 is the amount of compound in the dispenser at the beginning of evaporation, Ct is the amount of compound at time t, and k is the evaporation rate constant. In case of a first-order kinetic, a half of the amount of the pheromonal compound will be evaporated after a time t1/2, called half-life of the compound (McDonough et al. , 1989; Möttus et al. , 2001).
Many studies were conducted to give an estimation of the release rate of pheromone over time from dispensers in specific experimental conditions. However, very few studies developed rate kinetic predictive models in function of physic-chemical features (temperature, relative humidity, wind speed…). Moreover, these experiments only considered one parameter at a time instead of treating the combined parameters in an experimental design to finally obtain a realistic modelization of release rate, close to the rate expected on the field. McDounough et al. (1992) described a modelization of pheromone release rate by determining the half-life times of dispensers in fixed conditions. Most recently, Alfaro-Cid et al. (2009) attempted to develop a pheromone dispenser (sex pheromone of codling moth, Cydia pomonella L. (Lepidoptera: Olethreutidae)) less sensitive to climatic conditions by modeling a relationship between rate and on-field measured temperature and humidity.
The results of some studies on release rate estimation or modelisation are summarized in Table 1. Some of them are described in more details hereafter:
Shem et al. (2009) studied the influence of temperature on the release rate of a blend of allomones derived from waterbuck odor, in a reservoir type dispenser, to control tsetse flies. As expected, the release rate increases in function of the temperature. The same was demonstrated by Atterholt et al. (1999) considering the release of oriental fruit moth pheromone from paraffin emulsions at three temperatures from 27°C to 49°C. It is noticeable that at the lower temperature, the release rate was constant over time (during 100 days). The release rate was higher at 38°C and 49°C but the difference between these two temperatures was little. However, the release rate decreased with time at higher temperatures due to pheromone oxidation and degradation phenomena.
Van der Kraan et al. (1990) determined the influence of temperature and air velocity on various types of dispensers releasing moth sex pheromones. The conclusions of this study were that the influence of temperature is more important than wind speed on the release rate. Nevertheless, the effect of air movement in natural environmental conditions could not be underestimated.
Many other studies were led in a goal to attempt a mathematical model of release rate in function of physic-chemical parameters. It is clear that the most influencing environmental parameter is temperature which modifies the speed of evaporation of volatile semiochemical compounds. However, for this factor and for the others (wind speed, relative humidity, UV light, oxygen), the influence on release rate is depending on the design of dispenser (shape, polymeric matrix, thickness…) and the semiochemical compound itself.
5. Conclusions
The determination of the evolution of slow-release rate as a function of environmental conditions, considering the influence of temperature, wind speed, relative humidity, sunlight, has to be processed case by case. Indeed, in practice, it is not possible to obtain a global mathematical model for all dispensers and compounds. Experiments conducted to approach the environmental conditions faced the constraint that the fluctuations observed in field are too unpredictable and random to be reproduced in laboratory. The laboratory studies can only predict limitations of use in fixed conditions and give theoretical information on longevity of lures.
The best way to estimate the release-rate efficiency is to regularly analyze field-aged dispensers in order to determine if the lower threshold limit of rate is attained. Ideally, theoretical modelization could be based on experimental designs (Box-Behnken design for e. g) taking into account the combination of various physico-chemical data.
In conclusion, the use of semiochemical slow-release devices to control pests requires the knowledge of numerous scientific fields going from the entomology to the technical implementation of dispensers.
Login or register to correct this text!
You can correct this text if you set follow language skills of English in settings: Native speaker, Proficiency
You can correct this text if you set follow language skills of English in settings: Native speaker, Proficiency
Please correct texts in English:
Please help with translation:
Arabic Armenian Azerbaijan Basque Belorussian Bosnian Bulgarian Catalan Chinese Croatian Czech Danish Dutch English Esperanto Estonian Finnish French Georgian German Greek Gujarati Hebrew Hindi Hungarian Icelandic Indonesian Italian Japanese Javanese Kazakh Korean Kyrgyz Latin Latvian Macedonian Malay Mongolian Norwegian (bokmal) Norwegian (Nynorsk) Persian Polish Portuguese Romanian Russian Sanskrit Serbo-Croatian Slovak Spanish Swedish Tatar Thai Turkish Ukrainian Uzbek Vietnamese Welsh