4.2

• Characteristics of insects that make them successful


  • Small size
  • A protective cuticle (exoskeleton)
  • An efficient nervous system (the blood-brain barrier and sensory neuromotor refinement)
  • The evolution of flight
  • High reproductive rate

  
• Exoskeleton


  A strong box that prevents desiccation, provides points for muscle attachment, and protects vital organs
• Exuvium


  The shed exoskeleton of an insect
• Why are Insects so Dominant and Successful?

  • Structure (exoskeleton)
  • Flight (only flying arthropods)
  • Small size
  • Reproductive capacity (high fecundity)
  • Adaptability (genetic, rather than behavioral)
• At least 80% of all animals are insects
• More than 900,000 described species, probably between 3-10 million actual species
• Insects inhabit virtually all terrestrial habitats, exceptions are arctic, Antarctic, and peaks of very high mountains
• Roles of Insects


  • Herbivores
  • Decomposers
  • Predators and parasitoids
  • Prey
  • Pollinators
  • Disseminators of other organisms (seeds)
• Herbivores


  • Feed on a vast array of food plants, major herbivores in natural ecosystems; 80% plant material ingested each year by herbivores
• Decomposers


  Mainly insect - decomposers fauna, Saprophagous (feed on dead or dying plant tissues, dead animals, and animal excrement)
• Predators


  • Generally larger than their prey, Consume many prey, All life stages can be predatory (immature and adult)
• Predator groups


  • Spiders (not an insect)
  • Predatory bugs
  • Predatory mites (not an insect)
  • Hoverflies
• Parasites


  Specialized in their choice of host, Only the female searches for host, Different parasitoid species can attack different life stages of host, Immatures almost always kill host, Live and feed in or on a larger host, Develop inside the host, Immatures remain on or in host; adults are free-living, mobile, and may be predaceous
• About 99% of all insect species are non-pests
• Beneficial (non-pest) roles of insects

  • Pollinators
  • Decomposers
  • Natural enemies (predators and parasitoids)
  • Producers of useful products
  • Specimens for scientific studies
  • Aesthetic value

  
• Why insects become pests

  • Change in cropping pattern which can result in some plant species being eliminated while new plants are being introduced
  • Larger areas of land are being utilized for planting which displaces other organisms in the area and can result to these organisms moving to another area
  • Change in human values and preferences
• Types of Feeding damage


  • Chewing type - defoliators
  • Boring type - make holes/tunnels
  • Sucking type - suck-up liquid/sap
• Chewing type - defoliators


  • Impact/extent of damage depends on extent of defoliation and plant growth stage/age, Some feed on fruits, stems and roots, Examples: caterpillars, beetles, grasshoppers, and leafminer
• Boring type

  • Make holes/tunnels, Signs: yellowing/wilting and drying of leaves, pitting and scarring, holes with frass/feces, Examples: Asian corn borer (ACB), eggplant fruit and shoot borer (EFSB), tomato fruitworm, and termites
• Sucking type


  • Suck-up liquid/sap, Hemipterans (true bugs); homopterans like aphids, scale insects, whiteflies, mealybugs, leafhoppers, Stunted growth, fewer leaves, wilting, drying and death, Some species have toxins in their saliva or transmit pathogens, Homopteran excrete honeydew which favors growth of sooty mold that alters photosynthesis
• Plant diseases vectored by insects