Annual loss of crop yields due to agricultural insect pests are approximately 10%.  Effective and safe management of insect pests would reduce the loss of crop production.  Insects live in an environment where they need to deal with biological and non-biological factors that impact their physiological and developmental activities to survive and expand their population.  These environmental factors include, but not limited to, phytochemicals in the host plants they feed on, toxic compounds, such as insecticides sprayed by human, parasitoid, microbes, temperature and drought stress.  In the long-term evolution, insects have developed sophisticated strategies to adapt the harmful factors against them.  For example, to feed on different host plants, insects develop effective and comprehensive olfactory and gustatory receptor systems and detoxification enzyme systems to deal with the secondary toxic phytochemicals.  These olfactory and gustatory receptor and detoxification enzyme systems contain multiple superfamilies of proteins and enzymes, such as cytochrome P450s, glutathione S-transferases (GSTs) and esterases, together to form multiple preventive and protection barriers along with the regulation and function of the endocrine systems, which synthesize and secrete hormones and neuropeptides circulating to the different target tissues and organs to guarantee the normal growth and development.  On the other hand, insects also adjust their feeding behaviors and metabolism pathways, as well as even the nutrient components in the host plants by changing the expression patterns of related genes to promote the nutrient intake and utilization.  Insects and their host plants ultimately establish a cooperative and antagonistic relationship during evolution. 
Insect development is coordinated by various hormones and neuropeptides.  The steroid hormone 20-hydroxyecdysone (20E) activates molting and metamorphosis, while juvenile hormone (JH) maintains larval status (Riddiford 1996; Riddiford et al. 2003).  These two hormones are the most critical hormones that regulate and balance the processes of growth, development and maturation of insects depending on their titers.  They often counteract each other in most of physiological events, but sometimes they also cooperate to regulate some activities, such as reproductive maturation.  20E and JH also involve in insect behavior, for example, feeding behavior, in which high level of 20E suppresses feeding, whereas high level of JH enhances feeding.  Insulin, along with JH, promotes larval growth by feeding more food and 20E opposes insulin and JH functions to initiate metamorphosis (Pan et al. 2018).  These three signal transduction pathways work together to maintain the growth and development on the right track.  Any interference on the intermediate steps in these pathways may result in arrest of the insect growth and development. 
Neuropeptides are a group of small protein molecules, usually synthesized and secreted from nervous systems to cells of the target tissues and organs, where they bind specific membrane receptors, for example, the G-protein-coupled receptors and initiate second-message cascades and then the distinct molecular responses.  It has been found that insect neuropeptides play crucial roles in feeding behavior, growth regulation, locomotor activity and sleep, ethanol sensitivity, learning and memory, aggression, courtship and reproduction, phase switch, osmotic and metabolic stress and hormone release (Nässel and Wegener 2011).
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