**10. Tritrophic interactions and its manipulation for IPM**

Plant quality can affect herbivore fitness directly (as food of herbivores) and indirectly (by affecting foraging cues for natural enemies) [12, 23]. Until recently, there has been a tenden‐ cy by those involved in IPM to be principally concerned with effects on herbivores or inter‐ actions between just two trophic levels [185]. However, interest in the importance of interactions among the three or four trophic levels (Figure 6) that characterize most natural systems and agroecosystems has been increased rapidly during the last two decades [26].

the control of *H. armigera* in different cropping systems. Therefore, we need to make a con‐ certed effort to transfer pest resistance into genotypes with desirable agronomic and grain characteristics. Recent achievements of genetics and molecular biology have been widely implemented into breeding new crop cultivars and brought in many various traits absent from parent species and cultivars. Furthermore, new progress in biotechnology makes it fea‐ sible to transfer genes from totally unrelated organisms, breaking species barriers not possi‐ ble by conventional genetic enhancement. Today, transgenic plants expressing insecticidal proteins from the bacterium *B. thuringiensis*, are revolutionizing agriculture. *Bacillus thurin‐ giensis* has become a major insecticide because genes that produce *B. thuringiensis* toxins have been engineered into major crops grown on 11.4 million ha worldwide (including soy‐ bean, cotton, peanut, tomato, tobacco, corn and canola). These crops have shown positive economic benefits to growers and reduced the use of other insecticides. Genetically engi‐ neered cottons expressing delta-endotoxin genes from *B. thuringiensis* offer great potential to dramatically reduce pesticide dependence for control of *Helicoverpa* spp. and consequently offer real opportunities as a component of sustainable and environmentally acceptable IPM systems [16]. Certainly, for sustainable management of *H. armigera* in soybean cropping sys‐ tems, such soybean resistant cultivars could play pivotal role. Therefore, to achieve this goal, much works should be conducted in breeding new soybean cultivars expressing *Bt* toxins

The potential ecological and human health consequences of *Bt* crops, including effects on nontarget organisms, food safety, and the development of resistant insect populations, are being compared for *Bt* plants and alternative insect management strategies. However, *Bt* plants were deployed with the expectation that the risks would be lower than current or al‐ ternative technologies and that the benefits would be greater. Based on the data to date, these expectations seem valid [16]. The major challenge to sustainable use of transgenic *Bt* crops is the risk that target pests may evolve resistance to the *B. thuringiensis* toxins. *Helico‐ verpa armigera* is a particular resistance risk having consistently developed resistance to syn‐ thetic pesticides in the past [21]. For this reason a pre-emptive resistance management strategy was implemented to accompany the commercial release of transgenic cultivars. The strategy, based on the use of structured refuges to maintain susceptible individuals in the population, seeks to take advantage of the polyphagy and local mobility of *H. armigera* to achieve resistance management by utilizing gene flow to counter selection in transgenic crops. However, refuge crops cannot be treated with Bt sprays, and must be in close proxim‐ ity to the transgenic crops (within 2 km) to maximize the chance of random mating among

**10. Tritrophic interactions and its manipulation for IPM**

Plant quality can affect herbivore fitness directly (as food of herbivores) and indirectly (by affecting foraging cues for natural enemies) [12, 23]. Until recently, there has been a tenden‐ cy by those involved in IPM to be principally concerned with effects on herbivores or inter‐ actions between just two trophic levels [185]. However, interest in the importance of

against *H. armigera*.

262 Soybean - Pest Resistance

sub-populations [184].

**Figure 6.** Simple diagram of multitrophic interactions representing some important causal relationships among the trophic levels mediated by some important insect fitness parameters

It is interesting that many traditional cultural practices exert their effects through complex multitrophic interactions, but it is exactly this complexity that makes such systems difficult to assess experimentally or validate conclusively across a broad range of environments. For example, it has been demonstrated that toxic secondary compounds in an herbivore diet may affect development, survivorship, morphology and size of its natural enemies. This ef‐ fect of poor-quality plants can thus indirectly lead to poor-quality natural enemies [186].

As knowledge of interactions across multitrophic systems both in nature and in agroecosys‐ tems expands, researchers and pest management practitioners are beginning to find ways of manipulating interactions across different trophic levels in order to develop more sustaina‐ ble approaches to pest management. Accordingly, population ecologists are actively debat‐ ing the relative importance of bottom-up (resource-driven) and top-down (natural enemydriven) processes in the regulation of herbivores populations [22, 187, 188]. However, there are a number of key areas where manipulation of host plant-pest-natural enemy interactions could provide substantial benefits in pest management systems (manipulation of host plant quality, allelochemicals and crop diversification and genetic manipulation of insect) [26].

For many years, there was a widely held view that HPR should be seen as an integral com‐ ponent of IPM programmes, but it has been demonstrated that HPR is by no means always compatible with biological control [178]. The significant and growing evidence from funda‐ mental research in allelochemically mediated interactions hold substantial promise with re‐ gard to the development of novel IPM techniques. Allelochemicals mediated interactions in insect-host plant relationship have been recognized as the most important factors in the suc‐ cessful establishment of an insect species on a crop [189]. Furthermore, allelochemicals pro‐ duced by plants also have considerable influence on the prey/host selection behavior of natural enemies, so that plants, herbivores, and natural enemies are interconnected through the well-knit array of chemicals. The host plant volatiles play a key role in attracting/repel‐ ling or retaining the natural enemies, thereby causing considerable changes in pest popula‐ tions on different plant cultivars [190]. Hare [191] cited 16 studies where interactions between resistant cultivars and natural enemies (parasitoids) were studied and the out‐ comes show a spectrum of interactions, ranging from synergistic, to additive, to none appa‐ rent through to disruptive or antagonistic. Negative interactions can occur due to the presence of secondary chemicals that are ingested or sequestered by natural enemies feed‐ ing on hosts present on resistant or partially resistant plants [192]. For example, specific tox‐ ic components in partially resistant soybean plants can be particularly problematic in this regard [193]. In addition to allelochemicals, morphological traits of host plants such as tri‐ chome density and color complexion can affect insect fitness and effectiveness of its natural enemies. It was observed that plant cultivars were sufficiently differing in their trichome density and color complexion which were considered as main resource of variations in rate of parasitism on different plant cultivars. Cotton cultivars with low density of hairs on the upper leaf surface and high hair density on the lower leaf surface help in reduction of pest incidence [194]. The rates of parasitism were negatively associated with trichome density as revealed by Mohite and Uthamasamy [195]. In another study, Asifulla *et al.* [196] noticed higher parasitism by *T. chilonis* on *H. armigera* eggs in glabrous cotton species compared to hairy types.

environmental concern and has repeatedly led to the development of resistance in this pest as well as the deleterious effects on nontarget organisms and environment. The common trend to‐ wards reducing reliance on chemicals for control of insect pests in agriculture renewed world‐ wide interest in integrated pest management (IPM) programmes and it seems that in most areas the aim must be integrated management, particularly on crops such as soybean where *H. armigera* is part of a diverse pest complex. Accordingly, in this chapter we attempt to introduce basic elements for implementation of sustainable management of *H. armigera*. For this, we re‐ viewed the main findings of different researchers and in some cases present our data. Howev‐ er, our findings revealed that for successful management of *H. armigera*, more attention should be devoted to some basic information such as monitoring efforts, forecasting activities and eco‐ nomic thresholds. In addition, more studies are needed to evaluate potential of novel control measures including selective insecticides and sublethal doses, HPR and genetically modified soybean cultivars and microbial pathogens (especially commercial formulations of *B. thurin‐ giensis* and NPV) for control of this noctuid pest. However, for future outlook of integrated management of *H. armigera* in soybean cropping systems, the development and use of resistant cultivars will play a crucial role. In other words, more works should be conducted to evaluate resistance of soybean cultivars to *H. armigera* in field conditions. Moreover, a further need is to evaluate tritrophic interactions among the soybean cultivars, *H. armigera* and its natural ene‐ mies and new studies should be included to evaluate such interactions. However, the informa‐ tion gathered in the current chapter could be valuable for integrated management of *H.*

Integrated Management of *Helicoverpa armigera* in Soybean Cropping Systems

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

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*armigera* in soybean cropping systems.

Semi-Arid Tropics; 2006.

and Amin Sedaratian

varieties. Entomological Science 2009; 12 147-154.

Department of Entomology, Faculty of Agriculture, Tarbiat Modares University, Tehran,

[1] Sharma HC. Integrated Pest Management Research at ICRISAT: Present Status and Future Priorities. Andhra Pradesh: International Crops Research Institute for the

[2] Naseri B, Fathipour Y, Moharramipour S, Hosseininaveh V. Comparative life history and fecundity of *Helicoverpa armigera* (Lepidoptera: Noctuidae) on different soybean

\*Address all correspondence to: fathi@modares.ac.ir

**Author details**

Yaghoub Fathipour\*

Iran

**References**

In conclusion, as a novel strategy for IPM programmes, well understanding of multitrophic interactions is critical to develop the sustainable, less pesticide-dependent or pesticide-free pest management programmes [197]. In the interest of agricultural sustainability, tritrophic manipulation, as a distinct approach to biological or cultural control, is probably to be pri‐ oritized increasingly by both researchers and those responsible for the development and practical implementation of pest management programmes. This process will be facilitated if improvements in the understanding of crop-pest-natural enemy evolution and their inter‐ actions are achieved [26, 197]. Information in this regard are essential in finding out what role the plant play in supporting the action of natural enemies and how this role could be manipulated reserving the natural enemies.
