**4. Chemosensory stimulation in insects**

In insects, chemosensory stimulation occurs in various receptor organs via constant bombardment of chemical signals which improved the insect's ability to detect, discriminate, and distinguish innumerable different molecules as different odors. The insect receptor organs include antennae, mouthparts, and ovipositors. These receptors are very sensitive even for a few molecules of specific semiochemicals. Attraction (directed movement toward stimuli) and repulsion (directed movement away from stimuli) are the main insect responses to various odors. For field traps, insect catches not only occur via taxes but also via kineses (random movement). The insect can detect any odor by olfactory receptors located in the sensory organs including antennae, mouthparts, and ovipositors [27]. Various types of sensilla are recorded including trichodea, basiconica, styloconica, chaetica, etc. Knowledge of the types of sensilla on the antennae and mouthparts provides a foundation for understanding the olfaction and feeding preferences of herbivorous insect pests and subsequently can be useful for improving new control strategies for the target pests [28, 29]. The basic structure of sensillum is explored by [30] in **Figure 2**. The sensillum formed from the sensory neuron attached to branched cuticular pores (P) which allows odor passage. Sensillum pores act to filter molecules received from the airstream and concentrated it in the lumen of the sensillum and passed to branched neurons which convey impulses from and to the central nervous system.

In insects, the ability to discriminate different odors depends only on the evolutionary pressures of the molecules which stimulate the development of specific binding proteins (BPs) and specific receptor sites present on individual chemosensory neurons. This selectivity bestowed upon chemosensory neurons by the receptor types expressed represents one level of signal filtering in the insect's olfactory system. The olfaction mechanism in insects is summarized by [14] in **Figure 3**. In brief, a chemical signal crosses the sensillum lymph (SL) through a pore and then binds to highly specific binding proteins: pheromone binding proteins/

#### **Figure 3.**

*Simplified schematic concept of perireceptor events in the insect's chemosensory sensilla. Absorbed stimulus molecules diffuse from the sensillum surface through pores in the cuticle (C) into the sensillum lymph. There, they are taken up by odorant- or pheromone-binding proteins and are transported through the aqueous lymph until they reach a specific receptor molecule (R) on the outer dendritic membrane (DM). This activates dendritic ion channels via membrane-bound proteins (\*) and intracellular second messenger cascades such as cyclic guanosine monophosphate (cGMP), inositol trisphosphate (IP3), and Ca ions. Also, the stimulus molecule could degrade in the sensory lymphatic room by specific enzymes (E) into inactive metabolites so that it can no longer activate the receptor [35].*

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complex behaviors.

**Figure 4.**

*esophageal ganglion [36].*

**5. Utilization of olfactory communication in IPM**

*Pheromones and Chemical Communication in Insects DOI: http://dx.doi.org/10.5772/intechopen.92384*

odorant binding proteins (PBPs/OBPs). The signal-PBP/OBP-complex passes or is transported to the chemosensory neuron, where it binds to a specific olfactory receptor protein (OR or R) in the neuron membrane. These receptor proteins were identified in 1999 by [31, 32]. They all belong to the same "seven-transmembranedomain" protein family; however, they differ between taxa a great deal [33]. From a molecular perspective, binding to the OR activates so-called G-proteins, which are also located in the neuron membrane and part of a phosphorylation-dependent energy exchange, triggering a cascade of signaling reactions. These eventually lead to electrical impulses being sent down from the axon of the neuron to the antennal lobe (AL) (**Figure 4**). The AL is structured into a number of neuron groups (glomeruli) that are innervated separately and only in response to specific individual odors or classes of chemically similar ones [34]. Filtering of these signals is accomplished after reaching the AL glomeruli depending on their quality, quantity, and temporal and spatial characteristics. From the AL, specific patterns of neural activity are processed to higher integrative centers of the brain, such as the mushroom bodies (MBs; **Figure 4**), which are believed to be involved in the control of

*Schematic view of the central brain area of the honeybee showing the antennal lobes with their specific glomeruli (small circles). From the AL projection neurons (PN) send olfactory information into the mushroom bodies. The MBs are higher-order integration centers of olfactory, visual, and mechanosensory information and are believed to play a role in the control of complex behaviors as well as learning and memory. SOG: Sub-*

Olfactory/chemical signals represent essential components in different insect management strategies including monitoring, mass trapping, luring and killing, mating disruption, and push-pull strategy (stimulo-deterrent diversion). Also, host plant volatiles play an important role in IPM strategies as the main olfactory response of insect pests for determination of food, mates, and/or oviposition and hibernation sites [1]. Host plant volatiles are often induced by different environmental factors. For instance, the feeding process of herbivore may increase emission of volatiles in plants; these volatiles are referred to as herbivore-induced plant volatiles that stimulate natural enemies to find their prey as illustrated in **Figure 5** [37].

#### **Figure 4.**

*Pests, Weeds and Diseases in Agricultural Crop and Animal Husbandry Production*

*Simplified schematic concept of perireceptor events in the insect's chemosensory sensilla. Absorbed stimulus molecules diffuse from the sensillum surface through pores in the cuticle (C) into the sensillum lymph. There, they are taken up by odorant- or pheromone-binding proteins and are transported through the aqueous lymph until they reach a specific receptor molecule (R) on the outer dendritic membrane (DM). This activates dendritic ion channels via membrane-bound proteins (\*) and intracellular second messenger cascades such as cyclic guanosine monophosphate (cGMP), inositol trisphosphate (IP3), and Ca ions. Also, the stimulus molecule could degrade in the sensory lymphatic room by specific enzymes (E) into inactive metabolites so that* 

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**Figure 3.**

**Figure 2.**

*Basic structure of sensillum [30].*

*it can no longer activate the receptor [35].*

*Schematic view of the central brain area of the honeybee showing the antennal lobes with their specific glomeruli (small circles). From the AL projection neurons (PN) send olfactory information into the mushroom bodies. The MBs are higher-order integration centers of olfactory, visual, and mechanosensory information and are believed to play a role in the control of complex behaviors as well as learning and memory. SOG: Subesophageal ganglion [36].*

odorant binding proteins (PBPs/OBPs). The signal-PBP/OBP-complex passes or is transported to the chemosensory neuron, where it binds to a specific olfactory receptor protein (OR or R) in the neuron membrane. These receptor proteins were identified in 1999 by [31, 32]. They all belong to the same "seven-transmembranedomain" protein family; however, they differ between taxa a great deal [33]. From a molecular perspective, binding to the OR activates so-called G-proteins, which are also located in the neuron membrane and part of a phosphorylation-dependent energy exchange, triggering a cascade of signaling reactions. These eventually lead to electrical impulses being sent down from the axon of the neuron to the antennal lobe (AL) (**Figure 4**). The AL is structured into a number of neuron groups (glomeruli) that are innervated separately and only in response to specific individual odors or classes of chemically similar ones [34]. Filtering of these signals is accomplished after reaching the AL glomeruli depending on their quality, quantity, and temporal and spatial characteristics. From the AL, specific patterns of neural activity are processed to higher integrative centers of the brain, such as the mushroom bodies (MBs; **Figure 4**), which are believed to be involved in the control of complex behaviors.
