16.4.3. Neuropeptides and insect control

Insect neuropeptides are small peptides that regulate most aspects of development, metabolism, homeostasis, and reproduction. Their diverse functions have been summarized in Table 3.1. Although neuropeptides are unlikely to be used as insecticides per se, knowledge of their chemistry and biological actions can be applied in novel approaches to insect control. Neuroendocrine manipulation involves disrupting one or more of the steps of the general hormone process of synthesis— secretion—transport—action—degradation. For example, developing an agent to block or over-stimulate at the release site could alter the secretion of a neuropeptide. Alternatively, the peptide-mediated response at the target tissue could be blocked or over-stimulated by a peptide mimic.

Furthermore, the protein nature of neuropeptides makes them amenable to control using recombinant DNA technology and genetic engineering. However, neuropeptides produced by transgenic crop plants or bacteria that express neuropeptide genes must be able to penetrate either the insect gut or cuticle. Manipulation of insect viruses appears more promising for control. Neuropeptide or “anti-neuro-peptide” genes could be incorporated into the genome of insect-specific viruses, which then would act as expression vectors of the genes to produce and release the insect hormone(s) within infected insect cells. Baculoviruses have the potential to be used in this way, especially in Lepidoptera. Normally, such viruses cause slow or limited mortality in their host insect (section 16.5.2), but their efficacy might be improved by creating an endocrine imbalance that kills infected insects more quickly or increases viral-mediated mortality among infected insects. An advantage of neuro-endocrine manipulation is that some neuropeptides may be insect- or arthropod-specific — a property that would reduce deleterious effects on many non-target organisms.

Table 3.1. Examples of some important insect physiological processes mediated by neuropeptides.

(After Keeley & Hayes 1987; Holman et al. 1990; Gäde et al. 1997; Altstein 2003.)

Growth and development
Allatostatins and allatotropinsInduce/regulate juvenile hormone (JH) production
BursiconControls cuticular sclerotization
Crustacean cardioactive peptide (CCAP)Switches on ecdysis behavior
Diapause hormone (DH)Causes dormancy in silkworm eggs
Pre-ecdysis triggering hormone (PETH)Stimulates pre-ecdysis behavior
Ecdysis triggering hormone (ETH)Initiates events at ecdysis
Eclosion hormone (EH)Controls events at ecdysis
JH esterase inducing factorStimulates JH degradative enzyme
Prothoracicotropic hormone (PTTH)Induces ecdysteroid secretion from prothoracic gland
Puparium tanning factorAccelerates fly puparium tanning
Antigonadotropin (e. g. oostatic hormone, OH)Suppresses oocyte development
Ovarian ecdysteroidogenic hormone (OEH = EDNH)Stimulates ovarian ecdysteroid production
Ovary maturing peptide (OMP)Stimulates egg development
Oviposition peptidesStimulate egg deposition
Prothoracicotropic hormone (PTTH)Affects egg development
Pheromone biosynthesis activating neuropeptideRegulates pheromone production (PBAN)
Metabolic peptides (= AKH/RPCH family)
  Adipokinetic hormone (AKH)Releases lipid from fat body
  Hyperglycemic hormoneReleases carbohydrate from fat body
  Hypoglycemic hormoneEnhances carbohydrate uptake
  Protein synthesis factorsEnhance fat body protein synthesis
Diuretic and antidiuretic peptides
  Antidiuretic peptide (ADP)Suppresses water excretion
  Diuretic peptide (DP)Enhances water excretion
  Chloride-transport stimulating hormoneStimulates Cl absorption (rectum)
  Ion-transport peptide (ITP)Stimulates Cl absorption (ileum)
Myotropic peptides
CardiopeptidesIncrease heartbeat rate
Kinin family (e. g. leukokinins and myosuppressins)Regulate gut contraction
ProctolinModifies excitation response of some muscles
Chromatotropic peptides
Melanization and reddish coloration hormone (MRCH)Induces darkening
Pigment-dispersing hormone (PDH)Disperses pigment
CorazoninDarkens pigment

Chapter 16