**1. Introduction**

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As part of minimizing the risk of crop losses due to herbivorous arthropods (here, mainly referring to insects and mites), most of the World's commercial food production systems are subjected to several applications of pesticides before being harvested. Some crops are sprayed 10-20 times, while most field crops are sprayed 1-5 times during the growing sea‐ son. In the US alone, the average number of insecticide applications ranges from 1-3 for most of the major field crops, and the total annual costs of pesticide applications exceed \$1.3 billion ([1], U.S. Department of Agriculture agricultural statistics services: www.nass.us‐ da.gov/). Several large ag-producing countries publish extensive details on insecticide use, including Australia, and the data presented below were collected from a public website (http://usda01.library.cornell.edu/usda/nass/AgriChemUsFruits//2000s/2008/AgriChemUs‐ Fruits-05-21-2008.pdf) on pesticide applications in the US in 2006. A somewhat extreme but also important example is the fresh sweet maize production in the US, which was grown on about 85,000 ha. Based on data from 14 US states, 20 different active ingredients of herbi‐ cides were applied an average 1.04 times to fresh sweet maize and amounted to about 2.6 kg of active ingredients of herbicides per ha. The same data suggested that about 3.5 kg of 23 different active ingredients of insecticides were applied on average 2.10 times per ha. Simi‐ larly, tomato fields (grown on about 42,000 ha in the US in 2006) were treated with 12 differ‐ ent active ingredients of herbicides, which were applied, on average, 1.14 times and the equivalent of about 0.7 kg of active ingredients per ha. Regarding insecticides, the same to‐ mato fields were treated with 32 different active ingredients, which were applied an average of 3.6 times and equal to about 4.9 kg of active ingredients per ha. While tomatoes and sweet corn may be close to the top of the list of growing crops receiving pesticide treatments, cau‐ liflower, celery, and many other horticultural crops and fruits are also subjected to intensive pesticide spraying regimes. Thus, farmers acknowledge that weeds and arthropods can po‐ tentially cause significant economic losses, and total pesticide application costs are low

© 2013 Nansen and Ridsdill-Smith; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Nansen and Ridsdill-Smith; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

enough to economically justify a very significant and consistent number of applications in almost all crops. It is beyond the scope of this chapter to address the gradually growing market for organic produce and the possible human health and environmental impacts of intensive pesticide spraying regimes. However, it is worth mentioning that – going back to the fresh sweet maize – applying 47 different active ingredients of pesticides (insecticides = 23, herbicides = 20, and fungicides = 4) at a total dosage of 6,7 kg per ha means that (assum‐ ing a maize plant density around 65,000 per ha and that about 50% of the applied pesticide ended up on treated plants) each maize plant received about 0.3 g of active ingredient of agrochemicals. How much active ingredient ends up in the edible portions of crops varies considerably based on exposure of the harvested plant part, the longevity of chemicals (re‐ sidual effect) and timing of applications in relation to harvest time. Extensive research ef‐ forts are being committed to the short and long term effects of pesticide residues in the food products [2, 3]. Despite high levels of pesticides being applied, it is encouraging that public‐ ly available reports, like http://www.ewg.org/foodnews/, suggest that fresh sweet maize does not contain detectable levels of pesticide residues. However according to the same re‐ port, other food products (i.e. apples, celery, and bell peppers) quite frequently test positive for pesticide residues.

they might as well add a low-cost insecticide to the tank mix and possibly get an added ben‐ efit. Estimates suggest that insecticide applications constitute 2-10% of the crop yield [5-7], but use of tank mixtures obviously decreases the overall application costs. The three exam‐ ples provided ("good growing season", value of seeds, and tank mixing) are important, be‐ cause they are not directly related to actual estimates of the pest population density, but they may still lead to a grower applying insecticides. That is, they are factors that raise the concern about possible pest infestations ("good growing season", value of seeds), or they provide economic justification (tank mix) of a pesticide spray application, irrespectively of whether pest populations have been detected in fields. Finally, it is worthwhile to highlight a psychological dimension to pesticide applications, which is that applying pesticides rather than "doing nothing" may give farmers the feeling of "doing something" (in this case spray‐ ing pesticides). This aspect is of particular importance in cropping systems in which sam‐ pling/monitoring programs are either not an important part of the operational practices, and/or they are deemed practically unfeasible. Increasing sizes of farms mean that the grow‐ er may only get to a certain portion of a field every 2-3 weeks or at even less frequent occa‐ sions. Obviously, many things can go wrong in a field that is unattended for long time periods, so growers may feel that they cannot afford NOT to apply insecticides – simply as a preventative measure. Frequent and widespread applications of insecticides are understand‐ able, when very little is known about the actual pest population density, large farming areas are managed by only a few people, and when an insecticide can be easily added at a low cost to an existing spray application. Thus, even though growers are generally considered to be "conservative" in their management style, the brief review above clearly outlines many operational and agronomical factors reasons why most crops are treated with numerous in‐ secticide applications in each growing season. Growers are generally low-risk takers, and are therefore accepting to spend considerable resources on pesticide applications according

The Performance of Insecticides – A Critical Review

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to a philosophy of rather safe than sorry.

**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‐

Several environmental and agronomic/operational factors affect the likelihood of insecti‐ cides being applied to a crop. For instance, a comparatively "good growing season", with the right amount and ideal seasonal distribution of rainfall, is equivalent to a high yield po‐ tential. A high yield potential means increased risk of potentially high losses incurred by ar‐ thropods and weeds, so growers are typically more inclined to apply pesticides to protect a high yield potential. In addition, a "good growing season" may also be conducive to growth of weeds and arthropod pests, which further increases the justifications for applying pesti‐ cides, even as a precautionary measure. Among the agronomic factors affecting the likeli‐ hood of insecticides being applied, the price of seeds is quite important. A grower may, especially if the prediction is to have a good growing season, decide to plant high-value seeds due to their high yield potential, or because those seeds possess a particular qualita‐ tive trait. Similarly, the grower may decide to apply additional (expensive) fertilizer to en‐ sure that the crop grows and yields to its full potential. Planting high-value seeds and "investing" in the crop by applying high levels of fertilizer generally means that growers have lower threshold tolerances for losses incurred. That is, as described in the conventional description of economic injury level and action threshold [4], there is generally a negative relationship between overall value of the crop and the likelihood of pesticides being applied as growers want to protect the growing crop. In other words, investing in high-yielding seeds under favourable conditions may be associated with additional crop protection inputs (such as, pesticide, irrigation, and fertilizer applications), because growers want to take full advantage of the yield potential of the given crop. Another factor increasing the likelihood of insecticide applications is the convenience of "tank mixtures", in which multiple agrochemicals are applied simultaneously. For instance, growers may decide to spray a herbi‐ cide just before crop emergence and decide to add a residual insecticide to the formulation to target establishment pests that may or may not be present. That is, growers want to opti‐ mize labour and fuel costs, so if they are going to spray fertilizer or herbicides anyway – they might as well add a low-cost insecticide to the tank mix and possibly get an added ben‐ efit. Estimates suggest that insecticide applications constitute 2-10% of the crop yield [5-7], but use of tank mixtures obviously decreases the overall application costs. The three exam‐ ples provided ("good growing season", value of seeds, and tank mixing) are important, be‐ cause they are not directly related to actual estimates of the pest population density, but they may still lead to a grower applying insecticides. That is, they are factors that raise the concern about possible pest infestations ("good growing season", value of seeds), or they provide economic justification (tank mix) of a pesticide spray application, irrespectively of whether pest populations have been detected in fields. Finally, it is worthwhile to highlight a psychological dimension to pesticide applications, which is that applying pesticides rather than "doing nothing" may give farmers the feeling of "doing something" (in this case spray‐ ing pesticides). This aspect is of particular importance in cropping systems in which sam‐ pling/monitoring programs are either not an important part of the operational practices, and/or they are deemed practically unfeasible. Increasing sizes of farms mean that the grow‐ er may only get to a certain portion of a field every 2-3 weeks or at even less frequent occa‐ sions. Obviously, many things can go wrong in a field that is unattended for long time periods, so growers may feel that they cannot afford NOT to apply insecticides – simply as a preventative measure. Frequent and widespread applications of insecticides are understand‐ able, when very little is known about the actual pest population density, large farming areas are managed by only a few people, and when an insecticide can be easily added at a low cost to an existing spray application. Thus, even though growers are generally considered to be "conservative" in their management style, the brief review above clearly outlines many operational and agronomical factors reasons why most crops are treated with numerous in‐ secticide applications in each growing season. Growers are generally low-risk takers, and are therefore accepting to spend considerable resources on pesticide applications according to a philosophy of rather safe than sorry.

enough to economically justify a very significant and consistent number of applications in almost all crops. It is beyond the scope of this chapter to address the gradually growing market for organic produce and the possible human health and environmental impacts of intensive pesticide spraying regimes. However, it is worth mentioning that – going back to the fresh sweet maize – applying 47 different active ingredients of pesticides (insecticides = 23, herbicides = 20, and fungicides = 4) at a total dosage of 6,7 kg per ha means that (assum‐ ing a maize plant density around 65,000 per ha and that about 50% of the applied pesticide ended up on treated plants) each maize plant received about 0.3 g of active ingredient of agrochemicals. How much active ingredient ends up in the edible portions of crops varies considerably based on exposure of the harvested plant part, the longevity of chemicals (re‐ sidual effect) and timing of applications in relation to harvest time. Extensive research ef‐ forts are being committed to the short and long term effects of pesticide residues in the food products [2, 3]. Despite high levels of pesticides being applied, it is encouraging that public‐ ly available reports, like http://www.ewg.org/foodnews/, suggest that fresh sweet maize does not contain detectable levels of pesticide residues. However according to the same re‐ port, other food products (i.e. apples, celery, and bell peppers) quite frequently test positive

196 Insecticides - Development of Safer and More Effective Technologies

Several environmental and agronomic/operational factors affect the likelihood of insecti‐ cides being applied to a crop. For instance, a comparatively "good growing season", with the right amount and ideal seasonal distribution of rainfall, is equivalent to a high yield po‐ tential. A high yield potential means increased risk of potentially high losses incurred by ar‐ thropods and weeds, so growers are typically more inclined to apply pesticides to protect a high yield potential. In addition, a "good growing season" may also be conducive to growth of weeds and arthropod pests, which further increases the justifications for applying pesti‐ cides, even as a precautionary measure. Among the agronomic factors affecting the likeli‐ hood of insecticides being applied, the price of seeds is quite important. A grower may, especially if the prediction is to have a good growing season, decide to plant high-value seeds due to their high yield potential, or because those seeds possess a particular qualita‐ tive trait. Similarly, the grower may decide to apply additional (expensive) fertilizer to en‐ sure that the crop grows and yields to its full potential. Planting high-value seeds and "investing" in the crop by applying high levels of fertilizer generally means that growers have lower threshold tolerances for losses incurred. That is, as described in the conventional description of economic injury level and action threshold [4], there is generally a negative relationship between overall value of the crop and the likelihood of pesticides being applied as growers want to protect the growing crop. In other words, investing in high-yielding seeds under favourable conditions may be associated with additional crop protection inputs (such as, pesticide, irrigation, and fertilizer applications), because growers want to take full advantage of the yield potential of the given crop. Another factor increasing the likelihood of insecticide applications is the convenience of "tank mixtures", in which multiple agrochemicals are applied simultaneously. For instance, growers may decide to spray a herbi‐ cide just before crop emergence and decide to add a residual insecticide to the formulation to target establishment pests that may or may not be present. That is, growers want to opti‐ mize labour and fuel costs, so if they are going to spray fertilizer or herbicides anyway –

for pesticide residues.
