**2. Considerations regarding volumes of insecticide formulations**

Due to the emphasis and reliance on insecticide applications, it is worthwhile briefly review‐ ing some of the basic considerations regarding volume of insecticide formulations and other factors affecting spray coverage and canopy penetration, when insecticides are applied to growing agricultural crops [8, 9]. Insecticide labels provide information about required ap‐ plication rates for registered combinations of pests and crops and also about volumes of car‐ rier (most commonly water) to be used. Interestingly, these vary considerably mong countries, so the same pesticide may be applied at a considerable range of dosages among different countries [10]. "Adjuvants" are compounds added to spray applications with the purpose of increasing "stickiness" (adherence to crops), provide UV-light protection (in‐ crease the residual effect), increase crop leaf penetration, and/or modify droplet sizes (i.e. re‐ duce drift and increase canopy penetration). Use of adjuvants is therefore a very important aspect of spray application performance. Due to costs and logistics of transporting water, aerial fixed-wing insecticide sprays are applied with much lower spray volumes (rarely ap‐ plied in formulations above 50 L per ha) than when the same insecticides are applied with ground rigs (50-200 L per ha). Other more specialized insecticide delivery systems include fumigations of post-harvest products or of soils, seed treatments (insecticides coated onto planted seeds) and transgenic insertion of toxin producing genes into growing crop plants (i.e. genes from *Bacillus thuringiensis* in Bt crops). Aerial fixed-wing insecticide applications are often preferred modes of application, when large fields are treated and/or the crop cano‐ py is too high or dense for spray boom applications with a tractor. When insecticides are ap‐ plied with either aerial or ground rig sprays, the decision on volume of insecticide formulation to be applied to a given field is widely determined by operational considera‐ tions, including: 1) size of field, 2) availability and cost of labour, 3) current fuel price, 4) availability of water tanks and/or pumps near the field, 5) height of crop canopy, and 6) whether the insecticide has systemic properties or not (whether it is absorbed through leaf surfaces and translocated within the treated plant – if so, the performance of the insecticide application is perceived to be less influenced by spray coverage and canopy penetration). Other factors more directly linked to the actual pest include: 7) where in the canopy (vertical distribution) the insect pest is most abundant and therefore whether it is important to deliv‐ er the insect formulation to a certain portion of the canopy, and 8) the pest's diurnal move‐ ment behaviour and therefore whether the spray application has to be completed within a certain time window (for instance, if a pest is highly crepuscular). When applied with mod‐ ern spraying equipment, the application rate (volume of formulation per ha) is computer controlled mainly through three variables: spray nozzle output (typically delivering mean droplets of 0.05-0.5 µm), boom height above canopy, and speed of vehicle. The practical re‐ alities are that aerial insecticide sprays are cheapest but often require contracting of a profes‐ sional pilot. In Western Australia and many other important agricultural regions, aerial insecticide sprays are frequently about 10 liter per ha, which – assuming that all the spray formulation is deposited on the treated field – amounts to 1 ml per m2 . If that m2 has crop canopy (not bare ground), then its total surface area is obviously much higher. [11] exam‐ ined wheat plants planted at a seeding rate of 180 per m2 and with a specific leaf area of about 30 cm2 per plant, or the equivalent of 2 (both sides) × 180 plants × 30 cm2 = 1.08 m2 . Thus, the actual surface area per m2 was slightly above 2 m2 when taken the crop surface into account. Furthermore, weather variables are known to greatly impact insecticide spray depositions [1], and issues with pesticide drift are also widely documented [12]. Thus, it seems reasonable to suspect that at least 20% of the sprayed volume is "lost" (not deposited on the target crop but ends up elsewhere). Summarizing these simple calculations, even a fairly conservative estimate of an aerial spray application suggests that not more than 0.4 ml is applied per m2 to a growing crop. The question raised here is – how likely is it that all insecticide applications deliver enough insecticides to crop leaves so that target pest popula‐ tions are effectively controlled? In the US, most aerial spray applications are applied at rates around 50 liters per ha, so the spray deposition is likely higher but may still amount to ac‐ tive ingredient leaf coverage in very low concentrations. The calculations presented here may vastly underestimate loss of spray volume due to drift, and they may greatly underesti‐ mate leaf areas – especially in dense canopies, so actual spray depositions may be considera‐ bly lower. But adhering to the simple calculations presented above, a likely insecticide spray

application may consist of applying about 0.4 ml evenly to 1 m2 – which should convince most about the concern that is being raised. It is important to underscore that the active in‐ gredient (killing agent) is normally just a small proportion of the spray volume, so the

tact insecticide is applied – how likely is that target pests acquire a lethal dosage? And if a systemic insecticide is applied – how likely is that the concentration in the vascular tissue is high enough to kill the target pest? Two factors become quite important in the answers to such questions: 1) mobility of the target pest and 2) repellency of the insecticide formulation.

these simple calculations, even a fairly conservative estimate of an aerial spray application suggests that not more than 0.4 ml is applied per m2 to a growing crop. The question raised here is – how likely is it that all insecticide applications deliver enough insecticides to crop leaves so that target pest populations are effectively controlled? The calculations presented here may vastly underestimate loss of spray volume due to drift, and they may greatly underestimate leaf areas – especially in dense canopies, so actual spray depositions may be considerably lower. But adhering to the simple calculations presented above, a likely insecticide spray application may consist of applying about 0.4 ml evenly to 1 m2 – which should convince most about the concern that is being raised. It is important to underscore that the active ingredient (killing agent) is normally just a small proportion of the spray volume, so the amount of killing agent applied to each cm2 of leaf surface is likely in nanograms. If a contact insecticide is applied – how likely is that target pests acquire a lethal dosage? And if a systemic insecticide is applied – how likely is that the concentration in the vascular tissue is high enough to kill the target pest? Two factors become quite important in the answers to such questions: 1) mobility of the target pest and 2) repellency of the insecticide formulation. Clearly, dosages below 1 ml per ha are not evenly distributed within 1 m2 of crop, so the target pest will only get in direct contact with the active ingredient if distributions of insecticide formulation and of target pests are spatially correlated (i.e. both are most predominant in the same portion of the canopy), and/or the target pest is very mobile. The point is that heavy (almost exclusive) reliance on contact insecticide applications should be accompanied with strong interest and knowledge about the possible performance and constraints. Or put in bold terms, just because a tractor with a boom sprayer travelled through a field or an airplane flew over a field and a certain volume of

target pest will only get in direct contact with the active ingredient if distributions of insecti‐ cide formulations and of target pests are spatially correlated (i.e. both are most predominant in the same portion of the canopy), and/or the target pest is very mobile. The point is that heavy (almost exclusive) reliance on contact insecticide applications should be accompanied with strong interest and knowledge about the possible performance and constraints. Or put in bold terms, just because a tractor with a boom sprayer travelled through a field or an air‐ plane flew over a field and a certain volume of pesticide formulation was applied does not

 However, it should be pointed out that insecticides categorized as "contact insecticides" may not always require physical contact in order to cause target pest mortality. Contact insecticides are believed only to kill pests, when insects ingest or get in direct contact with the active ingredient. As an example, bifentrhin is in IRAC (http://www.irac-online.org/eClassification/) class 3A (pyrethroids and pyrethrins), which are sodium channel modulators, and bifenthrin is labelled as a contact insecticide. A simple study was conducted in which formulations of bifenthrin were transferred to a 2 ml Eppendorf tube, which was placed inside a 50 ml plastic container with a lid. We tested the following dosages (% by volume) of bifenthrin in separate trials: 0% (positive control), 0.02, 0.20, 2.00, and 20.00. The recommended application rate for control of redlegged earth mite [*Halotydeus destructor*  (Penthaleidae: Acari)] in Australia is 50-100 ml per ha in 50-200 L formulation per ha, and it is normally applied at about 100 ml in 100 L water, which is equivalent to 0.1% (by volume) (www.syngenta.com). Redlegged earth mites collected from a field site near York (Western Australia) were transferred to the 50 ml plastic container and provided a single leaf of a suitable host plant (common vetch, *Vicia sativa*). The rim of the Eppendorf tube containing the bifenthrin formulation was covered with vaseline, so that the redlegged earth mite could not get in direct contact with the insecticide formulation. The lid of the 50 ml plastic container was sealed, so that possible volatilization of the bifenthrin would saturate the air inside the 50 ml plastic container. After 24 hours, the status of the redlegged earth mites was assessed. The results from this bioassay showed a fairly standard log-scaled dosage response in which all redlegged earth mites succumbed when the bifenthrin dosage exceeded 0.2% (Fig. 1). This simple study highlights important characteristics associated with certain "contact" insecticides, like pyrethroids, as they may actually suppress target pests due to volatilization – i.e. creating a scarce cloud within the crop canopy. And returning to the calculations of applications per m2 described above, volatilization may, at least partially, explain how it is possible that insecticide applications applied at a dosage below 1 ml per m2 are able to provide successful pest control. However, the simple laboratory experiment was conducted in sealed containers, and it is unknown to what extent the micro-environment inside the sealed containers reflects field conditions. More research is needed to investigate the possible roles of factors like insecticide concentration and droplet size on

However, it should be pointed out that insecticides categorized as "contact insecticides" may not always require physical contact in order to cause target pest mortality. Contact in‐ secticides are believed only to kill pests, when insects ingest or get in direct contact with the active ingredient. As an example, bifentrhin is in IRAC (http://www.irac-online.org/eClassi‐ fication/) class 3A (pyrethroids and pyrethrins), which are sodium channel modulators, and bifenthrin is labelled as a contact insecticide. A simple study was conducted in which for‐ mulations of bifenthrin were transferred to a 2 ml Eppendorf tube, which was placed inside a 50 ml plastic container with a lid. We tested the following dosages (% by volume) of bifen‐

**Figure 1.** Redlegged earth mite mortality in response to bifenthrin dosage in no-contact bioassay

**Bifenthrin dosage (in %) 0.001 0.01 0.1 1 10 100**

are not evenly distributed within 1 m2

of leaf surface is likely in nanograms. If a con‐

The Performance of Insecticides – A Critical Review

http://dx.doi.org/10.5772/53987

199

of crop, so the

amount of killing agent applied to each cm2

necessarily mean that target pest control was accomplished.

Figure 1. Redlegged earth mite mortality in response to bifenthrin dosage in no-contact bioassay

pesticide formulation was applied does not necessarily mean that target pest control was accomplished.

Clearly, equivalent to 1-5 ml per m2

**Redlegged earth mite mortality**

**30**

**40**

**50**

**60**

**70**

**80**

**90**

**100**

application may consist of applying about 0.4 ml evenly to 1 m2 – which should convince most about the concern that is being raised. It is important to underscore that the active in‐ gredient (killing agent) is normally just a small proportion of the spray volume, so the amount of killing agent applied to each cm2 of leaf surface is likely in nanograms. If a con‐ tact insecticide is applied – how likely is that target pests acquire a lethal dosage? And if a systemic insecticide is applied – how likely is that the concentration in the vascular tissue is high enough to kill the target pest? Two factors become quite important in the answers to such questions: 1) mobility of the target pest and 2) repellency of the insecticide formulation. Clearly, equivalent to 1-5 ml per m2 are not evenly distributed within 1 m2 of crop, so the target pest will only get in direct contact with the active ingredient if distributions of insecti‐ cide formulations and of target pests are spatially correlated (i.e. both are most predominant in the same portion of the canopy), and/or the target pest is very mobile. The point is that heavy (almost exclusive) reliance on contact insecticide applications should be accompanied with strong interest and knowledge about the possible performance and constraints. Or put in bold terms, just because a tractor with a boom sprayer travelled through a field or an air‐ plane flew over a field and a certain volume of pesticide formulation was applied does not necessarily mean that target pest control was accomplished. these simple calculations, even a fairly conservative estimate of an aerial spray application suggests that not more than 0.4 ml is applied per m2 to a growing crop. The question raised here is – how likely is it that all insecticide applications deliver enough insecticides to crop leaves so that target pest populations are effectively controlled? The calculations presented here may vastly underestimate loss of spray volume due to drift, and they may greatly underestimate leaf areas – especially in dense canopies, so actual spray depositions may be considerably lower. But adhering to the simple calculations presented above, a likely insecticide spray application may consist of applying about 0.4 ml evenly to 1 m2 – which should convince most about the concern that is being raised. It is important to underscore that the active ingredient (killing agent) is normally just a small proportion of the spray volume, so the amount of killing agent applied to each cm2 of leaf surface is likely in nanograms. If a contact insecticide is applied – how likely is that target pests acquire a lethal dosage? And if a systemic insecticide is applied – how likely is that the concentration in the vascular tissue is high enough to kill the target pest? Two factors become quite important in the answers to such questions: 1) mobility of the target pest and 2) repellency of the insecticide formulation. Clearly, dosages below 1 ml per ha are not evenly distributed within 1 m2 of crop, so the target pest will only get in direct contact with the active ingredient if distributions of insecticide formulation and of target pests are spatially correlated (i.e. both are most predominant in the same portion of the canopy), and/or the target pest is very mobile. The point is that heavy (almost exclusive) reliance on contact insecticide applications should be accompanied with strong interest and knowledge about the possible performance and constraints. Or put in bold terms, just because a tractor with a boom sprayer travelled through a field or an airplane flew over a field and a certain volume of

plied in formulations above 50 L per ha) than when the same insecticides are applied with ground rigs (50-200 L per ha). Other more specialized insecticide delivery systems include fumigations of post-harvest products or of soils, seed treatments (insecticides coated onto planted seeds) and transgenic insertion of toxin producing genes into growing crop plants (i.e. genes from *Bacillus thuringiensis* in Bt crops). Aerial fixed-wing insecticide applications are often preferred modes of application, when large fields are treated and/or the crop cano‐ py is too high or dense for spray boom applications with a tractor. When insecticides are ap‐ plied with either aerial or ground rig sprays, the decision on volume of insecticide formulation to be applied to a given field is widely determined by operational considera‐ tions, including: 1) size of field, 2) availability and cost of labour, 3) current fuel price, 4) availability of water tanks and/or pumps near the field, 5) height of crop canopy, and 6) whether the insecticide has systemic properties or not (whether it is absorbed through leaf surfaces and translocated within the treated plant – if so, the performance of the insecticide application is perceived to be less influenced by spray coverage and canopy penetration). Other factors more directly linked to the actual pest include: 7) where in the canopy (vertical distribution) the insect pest is most abundant and therefore whether it is important to deliv‐ er the insect formulation to a certain portion of the canopy, and 8) the pest's diurnal move‐ ment behaviour and therefore whether the spray application has to be completed within a certain time window (for instance, if a pest is highly crepuscular). When applied with mod‐ ern spraying equipment, the application rate (volume of formulation per ha) is computer controlled mainly through three variables: spray nozzle output (typically delivering mean droplets of 0.05-0.5 µm), boom height above canopy, and speed of vehicle. The practical re‐ alities are that aerial insecticide sprays are cheapest but often require contracting of a profes‐ sional pilot. In Western Australia and many other important agricultural regions, aerial insecticide sprays are frequently about 10 liter per ha, which – assuming that all the spray

198 Insecticides - Development of Safer and More Effective Technologies

formulation is deposited on the treated field – amounts to 1 ml per m2

ined wheat plants planted at a seeding rate of 180 per m2

Thus, the actual surface area per m2

about 30 cm2

is applied per m2

canopy (not bare ground), then its total surface area is obviously much higher. [11] exam‐

into account. Furthermore, weather variables are known to greatly impact insecticide spray depositions [1], and issues with pesticide drift are also widely documented [12]. Thus, it seems reasonable to suspect that at least 20% of the sprayed volume is "lost" (not deposited on the target crop but ends up elsewhere). Summarizing these simple calculations, even a fairly conservative estimate of an aerial spray application suggests that not more than 0.4 ml

insecticide applications deliver enough insecticides to crop leaves so that target pest popula‐ tions are effectively controlled? In the US, most aerial spray applications are applied at rates around 50 liters per ha, so the spray deposition is likely higher but may still amount to ac‐ tive ingredient leaf coverage in very low concentrations. The calculations presented here may vastly underestimate loss of spray volume due to drift, and they may greatly underesti‐ mate leaf areas – especially in dense canopies, so actual spray depositions may be considera‐ bly lower. But adhering to the simple calculations presented above, a likely insecticide spray

per plant, or the equivalent of 2 (both sides) × 180 plants × 30 cm2 = 1.08 m2

to a growing crop. The question raised here is – how likely is it that all

was slightly above 2 m2

. If that m2 has crop

.

and with a specific leaf area of

when taken the crop surface

Figure 1. Redlegged earth mite mortality in response to bifenthrin dosage in no-contact bioassay **Figure 1.** Redlegged earth mite mortality in response to bifenthrin dosage in no-contact bioassay

pesticide formulation was applied does not necessarily mean that target pest control was accomplished.

 However, it should be pointed out that insecticides categorized as "contact insecticides" may not always require physical contact in order to cause target pest mortality. Contact insecticides are believed only to kill pests, when insects ingest or get in direct contact with the active ingredient. As an example, bifentrhin is in IRAC (http://www.irac-online.org/eClassification/) class 3A (pyrethroids and pyrethrins), which are sodium channel modulators, and bifenthrin is labelled as a contact insecticide. A simple study was conducted in which formulations of bifenthrin were transferred to a 2 ml Eppendorf tube, which was placed inside a 50 ml plastic container with a lid. We tested the following dosages (% by volume) of bifenthrin in separate trials: 0% (positive control), 0.02, 0.20, 2.00, and 20.00. The recommended application rate for control of redlegged earth mite [*Halotydeus destructor*  (Penthaleidae: Acari)] in Australia is 50-100 ml per ha in 50-200 L formulation per ha, and it is normally applied at about 100 ml in 100 L water, which is equivalent to 0.1% (by volume) (www.syngenta.com). Redlegged earth mites collected from a field site near York (Western Australia) were transferred to the 50 ml plastic container and provided a single leaf of a suitable host plant (common vetch, *Vicia sativa*). The rim of the Eppendorf tube containing the bifenthrin formulation was covered with vaseline, so However, it should be pointed out that insecticides categorized as "contact insecticides" may not always require physical contact in order to cause target pest mortality. Contact in‐ secticides are believed only to kill pests, when insects ingest or get in direct contact with the active ingredient. As an example, bifentrhin is in IRAC (http://www.irac-online.org/eClassi‐ fication/) class 3A (pyrethroids and pyrethrins), which are sodium channel modulators, and bifenthrin is labelled as a contact insecticide. A simple study was conducted in which for‐ mulations of bifenthrin were transferred to a 2 ml Eppendorf tube, which was placed inside a 50 ml plastic container with a lid. We tested the following dosages (% by volume) of bifen‐

that the redlegged earth mite could not get in direct contact with the insecticide formulation. The lid of the 50 ml plastic container was sealed, so that possible volatilization of the bifenthrin would saturate the air inside the 50 ml plastic container. After 24 hours, the status of the redlegged earth mites was assessed. The results from this bioassay showed a fairly standard log-scaled dosage response in which all redlegged earth mites succumbed when the bifenthrin dosage exceeded 0.2% (Fig. 1). This simple study highlights important characteristics associated with certain "contact" insecticides, like pyrethroids, as they may actually suppress target pests due to volatilization – i.e. creating a scarce cloud within the crop canopy. And returning to the calculations of applications per m2 described above, volatilization may, at least partially, explain how it is possible that insecticide applications applied at a dosage below 1 ml per m2 are able to provide successful pest control. However, the simple laboratory experiment was conducted in sealed containers, and it is unknown to what extent the micro-environment inside the sealed containers reflects field conditions. More research is needed to investigate the possible roles of factors like insecticide concentration and droplet size on thrin in separate trials: 0% (positive control), 0.02, 0.20, 2.00, and 20.00. The recommended application rate for control of redlegged earth mite [*Halotydeus destructor* (Penthaleidae: Acari)] in Australia is 50-100 ml per ha in 50-200 L formulation per ha, and it is normally applied at about 100 ml in 100 L water, which is equivalent to 0.1% (by volume) (www.syn‐ genta.com). Redlegged earth mites collected from a field site near York (Western Australia) were transferred to the 50 ml plastic container and provided a single leaf of a suitable host plant (common vetch, *Vicia sativa*). The rim of the Eppendorf tube containing the bifenthrin formulation was covered with vaseline, so that the redlegged earth mite could not get in di‐ rect contact with the insecticide formulation. The lid of the 50 ml plastic container was sealed, so that possible volatilization of the bifenthrin would saturate the air inside the 50 ml plastic container. After 24 hours, the status of the redlegged earth mites was assessed. The results from this bioassay showed a fairly standard log-scaled dosage response in which all redlegged earth mites succumbed when the bifenthrin dosage exceeded 0.2% (Fig. 1). This simple study highlights important characteristics associated with certain "contact" insecti‐ cides, like pyrethroids, as they may actually suppress target pests due to volatilization – i.e. creating a scarce cloud within the crop canopy. And returning to the calculations of applica‐ tions per m2 described above, volatilization may, at least partially, explain how it is possible that insecticide applications applied at a dosage below 1 ml per m2 are able to provide suc‐ cessful pest control. However, the simple laboratory experiment was conducted in sealed containers, and it is unknown to what extent the micro-environment inside the sealed con‐ tainers reflects field conditions. More research is needed to investigate the possible roles of factors like insecticide concentration and droplet size on volatilization as a possible mode of action in dense crop canopies, and it is unknown whether volatilization plays a major role across insecticide classes.

plane (spray volume of 48 liter per ha) and six with ground rig (spray volume of 194 liter per ha). During each spray application, 10 water sensitive spray cards were deployed at the top of the canopy in different parts of the field, and both average and range of spray cover‐ ages were analysed (N = 140). Canopy penetration data were also obtained from nine of the 14 commercial spray treatments by having additional spray cards placed about 15 cm from the bottom of the potato canopy. In a recent study conducted in Western Australia, we quantified the "potential spray coverage" of commercial spray rigs by placing water sensi‐ tive spray cards at the ground level in a bare field (Fig. 2c). Thus, there was no crop, so the

The Performance of Insecticides – A Critical Review

http://dx.doi.org/10.5772/53987

201

obtained spray coverage represented the highest possible under the given conditions.

Weather conditions were recorded, and spray volume (30-130 liter per ha), tractor speed (15-25 km/h) and nozzles type (various types tested) were experimentally manipulated to obtain spray data from a wide range of commercial spray scenarios. Spray data for this study were col‐ lected in three combinations of fields and locations, and we obtained data from 77 unique com‐ binations of spray conditions (location, date, spray volume, tractor speed, and nozzle types) and with four replicated spray cards for each combination (N = 308). Fig. 3a shows average spray coverage at the top of the canopy or above bare ground in response to spray volume, and,

0.001). Thus, despite high variability in spraying conditions, spray coverage is clearly driven by volume and reached about 40%, when the equivalent of 200 liter per ha was applied. Aver‐ age spray coverages for the three data sets (aerial and ground rig applications in Texas and ground rig applications in Western Australia) were examined, and spray coverage was divid‐ ed by the spray volume applied as a measure of spray performance (Fig. 3b). When applying spray formulations with airplanes, the spray coverage performance was about 0.15 (meaning that for each extra liter per ha, the spray coverage increased, on average, by 0.15%), while it was about 0.17 in experimental studies conducted in Western Australia and about 0.24 in ground rig applications in Texas. Thus in terms of "conversion efficiency" (converting spray volume into spray coverage), the ground rig applications in Texas appeared to be most efficient. In ad‐ dition to comparison of averages, it is important to examine the range of consistency (differ‐ ence between minimum and maximum) within a given spray application. This information is important, because it may be used to assess the risk of certain portions of treated fields receiv‐

= 0.790, F = 340.48, P <

**Figure 2.** Ground spray rig applications and use of water sensitive spray cards

as expected, there was a highly positive correlation (df = 1,90, adjusted R2
