Economic decision rules for IPM

1. The establishment of the IPM concepts of EIL 8 ET by Stern et al was done in 1959. These concepts are widely recognized as the most important concepts in IPM. * Given the centrality of economic decision rule concept of IPM, it follows that every IPM program should be based on these concepts. In this chapter, we will argue that EILs should be incorporated much more into IPM programs and that EILs are central to the contributed development of environmental & economic sustainability concepts so important to IPM. Levels of economic decision for IPM: The concept of tolerating pest injury was not introduced by Stern et al. (1959). However, in response to failures in pest control in California because of insecticides resistance by pests and insecticides mortality of natural enemies, Stern et al. (1959) first proposed the fundamental concepts of the EIL, the ET, the economic damage & the pest status. The economic damage is defined as the amount of injury that will justify the cost of control. EIL & ET were previously defined. 1 Economic decision rules for IPM

2. * EIL & ET are not the only approaches for pest management decision making, but many other sorts of decision models are possible. However, the factors used in establishing the EIL and ET are the same as those that must be considered in many pest management models. Moreover, the EIL & the ET are often incorporated into more complex management models. Therefore, the EIL & the ET have central roles in pest management decision making. The Economic Injury Level (EIL): It may be simplest concept of the applied ecology. It is a straightforward cost-benefit equation in which the costs (losses associated with managing of the pest) are balanced with the benefits (losses prevented by managing of the pest). * The EIL actually represents a level of injury but not a density of pests. However, numbers of pests / unit area are often used as an index for injury because this injury can be very difficult to sample and measure. Therefore, using pest numbers as an index, EIL may be expressed as: larvae / plant or beetles / sweep or grass weeds / 2 Econ. decision rules IPM (continue EILs)

3. meter square or moths / trap etc. * According to Pedigo et al. (1986), the most frequently used equation to determine the EIL is: EIL = C / VIDK Where C = management cost per production unit (e.g. Dollars / ha); V = market value per production unit (Dollars / Kg); I = injury per pest equivalent; D = damage per unit injury (Kg reduction / ha / injury unit) and K = proportional reduction in injury with management. * It is important that these components are known so that pests can be managed effectively within an IPM program but because of the difficulty of determining I & D separately, both components often are determined together as simply loss per pest. * Variation in estimates of the damage relationship (how injury influences yield) follow from factors altering yield. The damage relationship (D) is the most variable component of the EIL and because injury- yield loss relationship can change most strikingly 3 Econ. decision rules IPM (continue EILs)

4. between wet & dry conditions where sufficient data are available separate EILs for normal & drought conditions may be determined. * Determining the damage relationship (D) is the most difficult and limiting aspect of EILs development because of environmental variability in yield responses; quantification of injury and treatments consisting of different levels of injury & replication over a minimum of 2 years. * The EILs value determines the injury level, most often in the form of pest density (pest management cost = cost from yield loss if no management occurs). For example, if EILs = 5 larvae / plant, the producers & other decision makers should not wait until the EILs has been reached because at that level, economic loss is already occurring. This is a common misunderstanding about the EILs. Therefore, the decision to initiate management activities (e.g. pesticides application) must be made before the EIL is reached so that the economic damage can be prevented. The prevention of economic damage is the sole rationale underlying the EIL concept. 4 Econ. decision rules IPM (continue EILs)

5. The Economic Threshold (ET): In many IPM programs, the decision to initiate the management action is based on the ET. Thus, the ET is the most widely used decision tool in IPM & in sometimes called the “decision threshold”. It is defined as the pest density at which management action should be taken. The ET is actually an index for when to implement pest management activities. For example, If an EIL is 10 larvae / plant, then an ET may be 8 larvae / plant and the action would be taken when 8 larvae per plant are sampled. This is not because that density represent s an economic loss but rather because it provides a window of time to take action before the pest density or injury increases to produce an economic loss. * Pedigo et al. (1989) divided ETs into 2 categories: 1) Subjective ETs and 2) Objective ETs. Characteristic of Subjective ETs: * They are not based on calculated EILs but rather on human experience, * they are practically always static values (e.g. 2 larvae / sweep net sample regardless of changes in market value of the commodity & control cost). These subjective ETs are called nominal thresholds & most commonly used. Characteristics of Objective ETs: * They are based on 5 Econ. decision rules IPM (continue ET)

6. calculated EILs so they are inherently dynamic; * They are subdivided into 3 categories: fixed, descriptive and dichotomous. * Fixed ETs are set at some percentage of the EIL and change proportionally with it (e.g. a fixed ET is 80 % of the EIL value). * Descriptive ETs are based on estimates of pest population growth & dynamics and rely on accurate sampling to determine if the population will be likely to exceed the EIL. * Dichotomous ETs are based on statistical procedures to classify a pest population as “economic” or “non-economic”. The time-sequential sampling technique is the best known example of dichotomous ET. * Because an ET represents a time to take action, it is best suited for use with a regular sampling program. In some formal sampling / decision making procedures (e.g. sequential sampling), the ET is essential for establishing decision points. With less sophisticated procedures, the ET still provides a benchmark against which pest densities are assessed. 6 Econ. decision rules IPM (continue ET)

7. Limitations of EILs & ETs: According to Pterson & Higley (2002), “the use of EILs & ETs is much more limited when pests almost always cause economic damage; when reliable sampling of injury or pests is difficult and when curative action is difficult or not available”. * Most pests that almost always cause economic damage often called perennial pests, directly infest the marketable product. The damage that they produce results in low EILs so they are practically unusable. * Sampling is difficult for many pests (e.g. many plant pathogens). The difficulties in quantifying plant pathogens have hindered EILs development. * There are also considerable difficulties in assigning economic values to the market value of some host plants (e.g. ornamentals or landscape trees. The economic value of a reduction in a host aesthetics is subjective & difficult to quantify but it can be done using AILs. * Other limitations include the relatively high cost of conducting the research necessary to determine the EILs and a lack of knowledge about the interaction between biotic & abiotic stresses on the host 7 Econ. Deci. rules IPM (EILs & ETs)

8. especially for plants. Current Approaches Because of its applicability to many situations, advances in EILs concept have occurred principally through extension of the model advanced by Pedigo et al. (1986). Aesthetic injury levels (AILs) have been determined based on attributes not readily definable in economic terms such as form, color, texture and beauty. Examples of resources in which AILs could be used include lawns, ornamental plants, homes & public buildings. Results obtained have revealed that public tolerance of pest injury is low resulting in low AILs with acceptable levels of injury at or less than 10%. However, the salient point is that thresholds can be developed based on aesthetic considerations. * In early1990s, environmentally based EILs were developed. Each variable in the EIL equation reflects management activities that could be manipulated to potentially enhance environmental sustainability. In this respect, researchers have suggested incorporating environmental costs into the management cost variable (C). The resulting EILs have been termed Environmental Economic Injury Levels (EEILs). Work by 8 Econ. Deci. rules IPM (current approaches)

9. agricultural economists & others suggest that the value of the EEILs is providing relative risk information to users and providing an economic context for comparing management options rather than as a use/non-use criterion (like conventional EILs). * Important conceptual advances in the ET occurred in 1980s where the insect population estimates have been converted into insect injury equivalents (IIEs). IIE is the total injury potential of an individual pest if it were to survive through all injurious life stages. Injury equivalents are determined from estimates of pest population structure, pest density and injury potential. * Development of multiple-species EILs is the most challenging in IPM. These EILs can provide decision makers with the ability to manage a complex of pests instead of managing single pest species. The primary advances in this area have involved integrating pest injury from different species by determining if the multiple-species injury has similar effects on the host. To develop multiple-species EILs using this concept, pest species must produce a similar type of injury ; produce injury within the same 9 Econ. decision rules IPM (continue

10. physiological time-frame of the host; produce injury of a similar intensity and affect the same plant part. * A recent development in the EIL is the probabilistic EIL (PEIL). It is defined as an EIL that reflects its probability of occurrence which is determined by incorporating the variability and uncertainty associated with the input variables used to calculate the EIL. * The practical value of the PEIL can be understood as follows: for bean leaf beetle (Cerotomatrifurcata) in seedling stage soybean, the PEIL chosen of 7.7 adults / plant means that an EIL less than 7.7 adults / plant will occur only 25% of the time, therefore the decision maker will use a sufficiently conservative EIL 75 % of the time. 10 Econ. decision rules IPM (continue)

11. * Cotton (Gossypium spp.) is the most important natural source of fiber in the world, it accounts for almost 40 % of total world production. The current top five producing countries (in order) are China, India, USA, Pakistan and Brazil. * In USA, Crop loss due to insects & mites has generally declined in the past ten years which represents a marked improvement in crop protection technologies & IPM practices. * Numerous reviews have previously summarized cotton insect pest management in USA. Also, this chapter summarizes current & recent past efforts in cotton IPM that continue to build upon > a century of scientific research & innovation based on ecological principles & understanding. * Cotton Pests & their damage: About 1300 herbivorous insects are known from cotton systems worldwide (many species are common inhabitants and still fewer are of economic importance). In USA, about 100 species of insects & spider mites are considered pests of cotton but only 20% of them are common and cause damage if they are left 11 IPM of Cotton Arthropod

12. uncontrolled, the remaining are sporadic or secondary pests. * Pest species vary from one production area to another, for example, Bollworm (Helicoverpazea) and tobacco budworm (Heliothisvirescens) are major pests of cotton in USA from Texas eastward while the pink bollworm (Pectinophoragossypiella) is the dominant bollworm in the western USA. Various species of Lygus and other mirid plant bugs affect cotton throughout the world. The pink bollworm, the cotton aphid (Aphis gossypii) and the tobacco whitefly (Bemisiatabaci) are significant pests of cotton throughout the world. Boll weevil (Anthonomusgrandis) is only found in Americas. * Although the level of crop loss may appear small, the economic impact can be enormous. For example, in 2005, the total yield reduction from arthropod pests in USA cotton was 4.47% (represented a loss of > 1.5 million bales of cotton valued at 1250 million dollars in yield reduction & control costs). One cotton bale = 218 Kg of lint. * Many factors have contributed to reductions in pest losses over the past 20 years including boll weevil eradication, transgenic cottons for 12 Econ. decision rules IPM (continue)

13. control of caterpillar pests and improved overall IPM programs for various pests. Beneficial Arthropods of cotton: many species of beneficial insects and spider mites are associated with cotton systems. In a study done at Arkansas cotton fields, about 600 species of arthropod predators including 160 species of spiders were found. Of these species, 300 species are parasitoids & arthropod predators. Like cotton herbivores, only a fraction of these are common such as big-eye bug (Geocorisspp.), anthocorid bugs (Orius spp.), damsel bugs (Nabis spp.), assassin bugs (Zelus and Sinea spp.), green lacewings (Chrysopa and Chrysoperla spp.), lady beetles (Hippodamia and Scymnus spp.), ants (especially Solenopsis spp.), parasitic wasps (Bracon spp.; Cotesia spp.; Microplitisspp.andTrichgramma spp.), flies (Archytas spp., Eucelatoria spp.) and a wide variety of web-building and wandering spiders. * We know about the important role of these natural enemies in cotton pest control but the most dramatic evidence of their impact comes from studies in which the destruction or disturbance of natural enemy 13 Econ. decision rules IPM (continue)

14. communities by indiscriminant insecticides use is associated with pesticides outbreak. Overall arthropod communities in cotton are dynamic and largely driven by the wide diversity of management options discussed below. * IPM programs and implementation in cotton systems: “Areawide programs” were applied at a large scale in IPM programs, for example, the effective control of boll weevil & the tobacco budworm when coordinated early-season treatments were applied in a community basis. Also, the successful control of tobacco whitefly (Bemisiatabaci) in the desert valleys of the western USA. * Case studies from IPM programs of cotton arthropod: Many examples of operational IPM programs for cotton pests are existing throughout the USA. Three representative examples will be highlighted as follows: 1) Whitefly IPM in Arizona: Bemisiatabaciis a polyphagous insect. Biotype B has major impacts on most agricultural production in the western USA. In response, a multi-component research & educational plan was launched that resulted in a successful IPM program which 14 Econ. decision rules IPM (continue)

15. continued to be expanded & refined today. The overall program can be envisioned, and is taught to growers & consultants as a pyramid with multiple, overlapping layers & components (Fig. 25.4). * The broad base of the pyramid, founded on research, emphasizes tactics and strategies that can be implemented to reduce overall pest populations including various crop management practices and selection of well-adapted, smooth-leaf varieties which are generally less attractive to whiteflies. The foundation also emphasizes natural enemy conservation through the use of selective control methods for whiteflies and other pests and an array of areawide tactics like crop placement and arrangement to reduce pest movement, destruction of crop residues and weeds & coordinated use of insecticides among all affected crops to manage resistance. * The two upper layers of the pyramid outline pest monitoring through an efficient binomial sampling scheme, and the timing of effective control methods based on ET and a three-stage insecticide use system which emphasizes selectivity (e.g. safety to beneficial arthropods) in the initial stages. Follow-up treatments are rarely needed if these 15 Econ. decision rules IPM (continue)

16. 16 Econ. decision rules IPM (continue)

17. selective options are used first because the conserved natural enemies & other natural forces are then able to suppress whitefly populations long term. * The three-stage system also implicitly encourages the rotation of insecticides with differing modes of action in order to mitigate resistance. Operationally, the IPM plan has significantly reduced insecticide use for all cotton pests in Arizona from a decades-long high of over 12 applications in 1995 at a cost of 536 US dollars per hectar to a decades low application rate of 1.4 at a cost of 77 US dollars per hectar in 2006. 2 ) Plant bugs and stink bugs management in midsouth & southeast USA: A plant bug complex including Lygus bug (Lyguslineolaris) and clouded plant bugs (Neurocolpusnubilis) has been a long-standing pest problem in midsouth & southeast USA cotton system. * Plant bugs attack cotton at early squaring but can persist as a pest problem through boll development. A complex of brown seed-feeding stink bugs (Euschistusservus) and green stink bugs (Acrosternum 17 Econ. decision rules IPM (continue)

18. hilare) and southern green stink bugs (Nezaraviridula) also attack maturing bolls later in the growing season. Both plant bugs & stink bugs are increasing in status but these tends to be more important in the midsouth and southeast, respectively. * The elevated importance of these polyphagus & mobile insects reflects success in eliminating boll weevil (through eradication) and tobacco budworm (by Bt cotton) as major pests. In 2006, crop loss & insecticidal use for these bug pests were twice to three-fold those of other pests across the midsouth & southeast. * Designing effective control measures for the bug complex has been a challenging task since these insects are resistant to several insecticides. The USDA in stoneville, Mississipi has an areawide approach to the removal of early season broadleaf hosts of tarnished plant bugs. This research approach has been evaluated by extension entomologists across the midsouth and is being adopted on limited hectares by growers in some regions. Additional testing is needed to confirm the broader impacts on other pest and beneficial species in the system. 18 Econ. decision rules IPM (continue)

19. * Extension entomologists in the southeast are developing treatment threshold and monitoring procedures for the stink bugs and those in the midsouth are studying sampling and management options for the plant bugs. 3) Eradication of pink bollworm from western USA: This insect is an exotic cotton pest that successfully invaded in USA in early 1900s and became firmly established in the West in the mid 1960s following various attempts to contain and suppress populations throughout the first half of the twentieth century. * The cooperative eradication program involves growers and state and federal agencies. The program is being implemented in phases beginning with west Texas, New Mexico & northern Chihuahua, Maxico in 2001 and continuing through Arizona to southern California and northern Sonora, Mexico in 2007 with the total program completed by 2010. * The basic elements of the program include mapping & monitoring of all cotton fields within each region and the use of a combination of Bt 19 Econ. decision rules IPM (continue)

20. transgenic cotton plants, mating disruption with pheromones, sterile insect release and follow-up insecticides as needed. * The sterile insect release in this case serves both to argument population control and as a substitute for the required non Bt refuge foe resistance management which was relaxed in Arizona & southern California to allow for 100% production of Bt cotton. * Pink bollworm populations in the phase I regions have been reduced by > 99% from 2001 to 2005, but it was too early, at that time, to gauge the overall success of the eradication sffort. 20 Econ. decision rules IPM (continue)