**5. Crucial role of economic thresholds for implementation of IPM programmes**

In most situations it is not necessary, desirable, or even possible to eradicate a pest from an area. On the other hand, the presence of an acceptable level of pests in a field can help to slow or prevent development of pesticide resistance and maintain populations of natural en‐ emies that slow or prevent pest population build-up. Therefore, the concepts of economic injury level (EIL) and economic threshold (ET [sometimes called an action threshold]) were developed (Figure 3). EIL and ET constitute two basic elements of the IPM [48]. Economic injury level was defined as the lowest population density that will cause economic damage [49]. The EIL is the most essential of the decision rules in IPM. In addition, the economic in‐ jury level provides an objective basis for decision making in pest management and the back‐ bone for the management of pests in an agricultural system is the concept of EIL [48]. Ideally, an EIL is a scientifically determined ratio based on results of replicated research tri‐ als over a range of environments. In practice, economic injury levels tend to be less rigorous‐ ly defined, but instead are nominal or empirical thresholds based on grower experience or generalized pest-crop response data from research trials. Although not truly comprehensive, such informal EILs in combination with regular monitoring efforts and knowledge of pest biology and life history provide valuable tools for planning and implementing an effective IPM programme. However, because growers will generally want to act before a population reaches EIL, IPM programmes use the economic threshold (Figure 3). The concept of eco‐ nomic threshold implies that if the pest population and the resulting damage are low enough, it does not pay to take control measures. In practice, the term economic threshold has been used to denote the pest population level at which economic loss begins to occur and indicate the pest population level at which pest control should be initiated [50].

**Figure 3.** Graph showing the relationship between the economic threshold (ET) and economic injury level (EIL). The arrows indicate when a pest control action is taken.

#### **5.1. EIL and ET for** *H. armigera* **on different crops**

system, region or country as well as the set of approaches and measures that are chosen to

**Figure 2.** The process of decision making in IPM. (after Reichelderfer *et al*. [47]) 1. The way in which control options are assessed will depend on the farmer's objectives. Subsistence farmers may select for a guaranteed food supply, while commercial farmers are more concerned with profit. 2. The number of options that a farmer can feasibly use will depend on the constraints set by the resources available. 3. Compare the cost-effectiveness of alternative practices.

In most situations it is not necessary, desirable, or even possible to eradicate a pest from an area. On the other hand, the presence of an acceptable level of pests in a field can help to slow or prevent development of pesticide resistance and maintain populations of natural en‐ emies that slow or prevent pest population build-up. Therefore, the concepts of economic injury level (EIL) and economic threshold (ET [sometimes called an action threshold]) were developed (Figure 3). EIL and ET constitute two basic elements of the IPM [48]. Economic injury level was defined as the lowest population density that will cause economic damage [49]. The EIL is the most essential of the decision rules in IPM. In addition, the economic in‐ jury level provides an objective basis for decision making in pest management and the back‐ bone for the management of pests in an agricultural system is the concept of EIL [48]. Ideally, an EIL is a scientifically determined ratio based on results of replicated research tri‐

**5. Crucial role of economic thresholds for implementation of IPM**

implement pest control programmes.

238 Soybean - Pest Resistance

**programmes**

Economic injury level and economic threshold of *H. armigera* on some crops was estimated by several researchers (Table 2). In the case of *H. armigera* on soybean, these thresholds are poorly defined and a little information in this regard is available. However, economic thresholds; especially economic injury level; are dynamic and can be varied from year to year or even from field to field within a year depending on crop variety, market conditions, development stages of plant, available management options, crop value and management costs (Table 2).


spp. Walden [66] presented the first comprehensive report on seasonal occurrence and abundance of the *Helicoverpa zea* (Boddie), based on light trap collections. Beckham [67] used light traps to index the populations of *Helicoverpa* spp. and reported that a significantly low‐ er percentage of the *Helicoverpa virescens* (Fabricius) populations responded to black-light

Integrated Management of *Helicoverpa armigera* in Soybean Cropping Systems

http://dx.doi.org/10.5772/54522

241

In the last few years, pheromone traps (containing virgin females or synthetic pheromones) have replaced light traps as moth-monitoring devices. These traps provide the pest manager with a convenient and effective tool for monitoring adult moth [68]. However, pheromone traps are highly efficient, simple to construct, inexpensive, and portable (requiring no pow‐ er). Furthermore, only the single species for which the trap is baited is attracted and caught, making identification and counting quick and easy. As an added bonus, pheromone traps also detect spring emergence of moths 2 or 3 weeks earlier than light traps, which should

Several group of researchers made the comparison of indexing populations of *Helicoverpa* spp. in light traps versus pheromone traps. There results revealed that light trap catches may index seasonal fluctuation of populations more accurately than pheromone traps, how‐ ever, pheromone traps are more sensitive to low populations early in the season and decline

There has been a considerable improvement into synthesis of the pheromones of *Helicoverpa* spp. in recent years. However, preliminary studies have already revealed that the catches in pheromone traps do not correlate very well with light-trap catches and field counts of the pest in all circumstances. In fact, trap catch data do not provide a quantitative threshold for intervention because a relationship between catch number and subsequent crop damage has

Egg count provides a better quantitative threshold for monitoring activity of *H. armigera* but egg desiccation, egg infertility or egg parasitism (biasing data) together with skill needed for field scouting, too often promote weak correlations between egg number and larval damage [71]. On the other hand, fruit inspection in the field has proved to be a valuable tool when develop against a number of fruit damaging pest species including *H. armigera* [72]. The ma‐ jor advantage of thresholds based on fruit inspection is that the short time between plant scouting for larval injury and fruit damage greatly increases correlation between both of these variables. Moreover, damaged fruit-count-based decision making may also be easily

Finally, we must now determine whether these pheromone traps are going to be of practical value in *Helicoverpa* management. For this, there is first a need to standardize trap design, pheromone dosage and release rates from the chosen substrate, and siting of the traps. As the next step, catches in these traps should be compared with other measures of *Helicoverpa* populations (light traps and actual counts of *Helicoverpa* eggs/larvae on the host plants in the same area). However, data from pheromone traps have already been shown to be valuable in some studies in the USA, where the data have been used in prediction models and have

lamps in traps than did *H. zea*.

give more precision to forecasts.

proved to be lacking in most cases [70].

learned and carried out by growers [70].

given useful information on the timing of infestations [64].

in efficiency with high populations late in the season [69].

**Table 2.** Economic threshold (ET) and Economic injury level (EIL) of *Helicoverpa armigera* on different crops.

### **6. Monitoring activity in integrated management of** *H. armigera*

In an IPM programme, pest managers use regular inspections, called monitoring, to collect the information they need to make appropriate decisions. A central idea in IPM is that a treatment is only used when pest numbers justify it, not as a routine measure. Keeping this in view, in IPM programmes, chemical control is applied only after visual inspection or monitoring devices indicate the presence of pests in that specific area, the pest numbers have exceeded the economic threshold (ET) and adequate control cannot be achieved with non-chemical methods within a reasonable time and cost. Therefore, it was considered that monitoring could reduce spraying costs by withholding a spray until a given threshold is reached [64].

For many years, light traps have been used to monitor *Helicoverpa* moth populations. Hart‐ stack *et al.* [65] developed a model for estimating the number of moths per hectare from these light-trap catches, to evaluate the possible use of light traps for controlling *Helicoverpa* spp. Walden [66] presented the first comprehensive report on seasonal occurrence and abundance of the *Helicoverpa zea* (Boddie), based on light trap collections. Beckham [67] used light traps to index the populations of *Helicoverpa* spp. and reported that a significantly low‐ er percentage of the *Helicoverpa virescens* (Fabricius) populations responded to black-light lamps in traps than did *H. zea*.

**Crop Economic threshold (ET) Economic Injury Level (EIL) References**

Chickpea - > 4 larvae / m2 [51]

Chickpea - 1.0 larva / m row [52]

Chickpea 1.0 larva / m row - [53]

Chickpea - 1 larva / 10 plants [54]

Chickpea - 0.6 larva / plant [55]

Chickpea 1.77 - 2.00 larvae / m row - [56]

Chickpea - 1.0 larva / m row [57]

Chickpea 0.81 larva / m row 1.1 larva / m row [58]

Pigeon pea - 0.78-0.80 larvae / plant [59]

Tomato 1.0 larva / plant - [60]

Cotton - 19.86 larvae / 100 plants [61]

Mung bean 1-3 larvae / m2 - [62]

Peanuts 4 larvae / m2 - [62]

Soybean - 8 larvae / m2 [63]

In an IPM programme, pest managers use regular inspections, called monitoring, to collect the information they need to make appropriate decisions. A central idea in IPM is that a treatment is only used when pest numbers justify it, not as a routine measure. Keeping this in view, in IPM programmes, chemical control is applied only after visual inspection or monitoring devices indicate the presence of pests in that specific area, the pest numbers have exceeded the economic threshold (ET) and adequate control cannot be achieved with non-chemical methods within a reasonable time and cost. Therefore, it was considered that monitoring could reduce spraying costs by withholding a spray until a given threshold is

For many years, light traps have been used to monitor *Helicoverpa* moth populations. Hart‐ stack *et al.* [65] developed a model for estimating the number of moths per hectare from these light-trap catches, to evaluate the possible use of light traps for controlling *Helicoverpa*

**Table 2.** Economic threshold (ET) and Economic injury level (EIL) of *Helicoverpa armigera* on different crops.

**6. Monitoring activity in integrated management of** *H. armigera*

reached [64].

240 Soybean - Pest Resistance

In the last few years, pheromone traps (containing virgin females or synthetic pheromones) have replaced light traps as moth-monitoring devices. These traps provide the pest manager with a convenient and effective tool for monitoring adult moth [68]. However, pheromone traps are highly efficient, simple to construct, inexpensive, and portable (requiring no pow‐ er). Furthermore, only the single species for which the trap is baited is attracted and caught, making identification and counting quick and easy. As an added bonus, pheromone traps also detect spring emergence of moths 2 or 3 weeks earlier than light traps, which should give more precision to forecasts.

Several group of researchers made the comparison of indexing populations of *Helicoverpa* spp. in light traps versus pheromone traps. There results revealed that light trap catches may index seasonal fluctuation of populations more accurately than pheromone traps, how‐ ever, pheromone traps are more sensitive to low populations early in the season and decline in efficiency with high populations late in the season [69].

There has been a considerable improvement into synthesis of the pheromones of *Helicoverpa* spp. in recent years. However, preliminary studies have already revealed that the catches in pheromone traps do not correlate very well with light-trap catches and field counts of the pest in all circumstances. In fact, trap catch data do not provide a quantitative threshold for intervention because a relationship between catch number and subsequent crop damage has proved to be lacking in most cases [70].

Egg count provides a better quantitative threshold for monitoring activity of *H. armigera* but egg desiccation, egg infertility or egg parasitism (biasing data) together with skill needed for field scouting, too often promote weak correlations between egg number and larval damage [71]. On the other hand, fruit inspection in the field has proved to be a valuable tool when develop against a number of fruit damaging pest species including *H. armigera* [72]. The ma‐ jor advantage of thresholds based on fruit inspection is that the short time between plant scouting for larval injury and fruit damage greatly increases correlation between both of these variables. Moreover, damaged fruit-count-based decision making may also be easily learned and carried out by growers [70].

Finally, we must now determine whether these pheromone traps are going to be of practical value in *Helicoverpa* management. For this, there is first a need to standardize trap design, pheromone dosage and release rates from the chosen substrate, and siting of the traps. As the next step, catches in these traps should be compared with other measures of *Helicoverpa* populations (light traps and actual counts of *Helicoverpa* eggs/larvae on the host plants in the same area). However, data from pheromone traps have already been shown to be valuable in some studies in the USA, where the data have been used in prediction models and have given useful information on the timing of infestations [64].
