CHAPTER 3 LECTURE 2 AND 3 [Autosaved].pptx

insect Biology and Diversity for Entomology

1. AGRI ENTOM 411 01 INSECT BIOLOGY AND DIVERSITY

2. Overview This chapter focuses on a special group of primitive insects called ametabolous insects, which are unique because they do not go through metamorphosis. When they hatch from eggs, they already look like small versions of the adults, only lacking size and reproductive ability. This simple way of developing shows how ancient and primitive they are compared to other insect groups. The four main orders discussed in this chapter are Thysanura , Diplura , Protura , and Collembola. Thysanura includes silverfish and firebrats, small insects that often live in houses and sometimes damage books or clothing. Diplura are eyeless soil insects with two tail-like appendages, important for breaking down organic matter. Protura are tiny insects without eyes and antennae, using their front legs as feelers to sense their surroundings. Collembola, or springtails, are very common in soil and are best known for their ability to jump using a special organ called the furcula. Although small and often unnoticed, these insects play a big role in nature. They help decompose dead materials, recycle nutrients, and keep the soil healthy. At the same time, they give scientists important clues about the early stages of insect evolution.

3. LEARNING OBJECTIVES By the end of this lesson, students should be able to: 1. Define ametabolous development and explain how it differs from other insect metamorphoses. 2. Identify and describe the four orders of ametabolous insects: Thysanura, Diplura, Protura, and Collembola. 3. Explain the general characteristics, habitat, and ecological significance of each order. 4. Appreciate the evolutionary importance of ametabolous insects in understanding insect origins.

4. Ametabolous Development Definition: Development without metamorphosis. Young insects resemble the adults in structure but are smaller and sexually immature. ·Key Features: No wings at any stage of life. Adults and nymphs look almost identical. Growth occurs mainly through molting. Considered primitive insects, often referred to as Apterygota (wingless insects). 03

5. Ametabolous Development 03

6. 04 Orders of Ametabolous Insects A . ORDER THYSANURA (SILVERFISH AND FIREBRATS) General Characteristics: Body elongated, flattened, covered with fine scales. Possess three long “tail-like” appendages at the end of the abdomen (two cerci and one median filament). Chewing mouthparts. Compound eyes present. Antennae long and thread-like. Wingless throughout life. Habitat: Found in dark, moist places such as under rocks, leaf litter, bathrooms, libraries, and old houses. Firebrats prefer warmer areas, while silverfish are common in humid indoor areas. Feeding: Feed on starchy materials, paper, glue, book bindings, and fabrics. Significance: Considered pests because they damage paper, books, and stored materials. Important for studying the early evolution of insects

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8. 04 B. Order Diplura (Two Bristletails) General Characteristics: Small, elongated, soft-bodied insects. Lacks eyes (blind). Antennae long and many-segmented. Abdomen ends with two long appendages (cerci), which may be filamentous or pincer-like depending on the species. Chewing mouthparts. ·Habitat: Found in moist soil, leaf litter, under stones, and decaying wood. Feeding: Mostly omnivorous: some feed on decaying matter, while others are predatory on small arthropods. Significance: Play a role in decomposition and soil nutrient cycling. Indicate soil health and biodiversity.

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10. 04 C. Order Protura (Coneheads) General Characteristics: Minute insects (0.5–2 mm long). Lack eyes and antennae. Front pair of legs are sensory and function like antennae. Mouthparts are entognathous (enclosed within the head capsule). Wingless. Habitat: Found in moist soil, leaf litter, mosses, and decaying organic matter. Feeding: Feed on fungal hyphae, spores, and decaying organic material. Significance: Contribute to soil fertility by breaking down organic matter. Represent an evolutionary step showing adaptation to soil habitats.

11. 04 C. Order Protura (Coneheads)

12. 04 D. Order Collembola (Springtails) General Characteristics: Small insects (usually less than 6 mm). Possess a unique forked jumping organ called the furcula, folded under the abdomen, used for leaping. Another organ, the collophore, located on the first abdominal segment, is used for water absorption and excretion. Eyes are simple or absent. Wingless. Habitat: Found in soil, leaf litter, decaying logs, fungi, and even on the surface of snow (“snow fleas”). Feeding: Feed on decaying plant material, fungi, algae, lichens, and pollen. Significance: Extremely abundant in soils and contribute to decomposition. Serve as bioindicators of soil health. Some species are pests in mushroom cultivation or greenhouses.

13. 04 D. Order Collembola (Springtails) General Characteristics: Small insects (usually less than 6 mm). Possess a unique forked jumping organ called the furcula, folded under the abdomen, used for leaping. Another organ, the collophore, located on the first abdominal segment, is used for water absorption and excretion. Eyes are simple or absent. Wingless. Habitat: Found in soil, leaf litter, decaying logs, fungi, and even on the surface of snow (“snow fleas”). Feeding: Feed on decaying plant material, fungi, algae, lichens, and pollen. Significance: Extremely abundant in soils and contribute to decomposition. Serve as bioindicators of soil health. Some species are pests in mushroom cultivation or greenhouses.

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15. Hemi-metabolous Hemi-metabolous insects represent one of the major types of insect development known as incomplete metamorphosis. These insects progress through three distinct life stages: egg, nymph, and adult (imago). Unlike holometabolous insects, they do not pass through a pupal stage. Instead, their immature forms—called nymphs—closely resemble the adults but are smaller, wingless, and sexually immature. As they grow, nymphs undergo several molts until they reach full maturity. This group includes several important insect orders such as Ephemeroptera (Mayflies), Odonata (Dragonflies and Damselflies), Plecoptera (Stoneflies), Orthoptera (Grasshoppers and Crickets), Phasmida (Stick and Leaf Insects), Dermaptera (Earwigs), and Embioptera (Webspinners). Each order displays unique structural adaptations and ecological functions, contributing to the stability and diversity of ecosystems. Overview

16. Hemi-metabolous Introduction Insects are the most diverse and abundant group of animals on Earth, occupying nearly every type of environment. One of the key features that distinguishes insects from one another is the type of metamorphosis they undergo during their life cycle. Hemi-metabolous, or incomplete metamorphosis, is a fascinating form of development where the transformation from juvenile to adult occurs gradually. The young nymphs often share similar habitats and feeding habits with the adults, allowing them to play continuous ecological roles throughout their lives. The study of hemi-metabolous insects provides valuable insights into insect evolution, adaptation, and environmental relationships. Many of these species—such as dragonflies and mayflies—are essential indicators of freshwater quality, while others like grasshoppers and crickets influence agriculture and serve as food sources for wildlife. Understanding their classification, characteristics, and ecological roles helps students appreciate the complexity of insect life and their importance in maintaining ecological balance

17. Learning Objectives 06 After completing this module, students should be able to: 1. Define hemi-metabolous metamorphosis. 2. Identify and describe the major insect orders under Hemi-metabolous development. 3. Recognize distinguishing features and examples of each order. 4. Appreciate the ecological importance of hemi-metabolous insects.

18. Hemi-metabolous 06 a. Order: Ephemeroptera (Mayflies) Metamorphosis Type: Hemi-metabolous Characteristics: Delicate, soft-bodied insects. Possess two or three long caudal filaments (tails). Adults have short lifespans (from a few hours to a few days). Immature stage (naiad) is aquatic. Habitat: Freshwater streams and rivers. Example: Ephemera danica (Common Mayfly). Ecological Role: Indicator of clean water quality.

19. Ephemeroptera 06

20. Hemi-metabolous 06 b. Orde r: Odonata (Dragonflies and Damselflies) Metamorphosis Type: Hemi-metabolous Characteristics: Large compound eyes, long slender abdomen, and two pairs of strong wings. Nymphs (naiads) are aquatic predators. Adults are strong fliers and beneficial as mosquito predators. Habitat: Near ponds, lakes, and streams. Example: Anax junius (Green Darner). Ecological Role: Control of mosquito populations.

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22. Hemi-metabolous 06 c. Order: Plecoptera (Stoneflies) Metamorphosis Type: Hemi-metabolous Characteristics: Long, slender insects with two pairs of membranous wings folded flat over the body. Nymphs are aquatic and have gills. Sensitive to pollution. Habitat: Clean, fast-flowing streams. Example: Pteronarcys dorsata (Giant Stonefly). Ecological Role: Bioindicator of freshwater ecosystem health.

23. Plecoptera 06

24. Hemi-metabolous 06 e. Order: Orthoptera (Grasshoppers, Crickets, Locusts, Katydids) Metamorphosis Type: Hemi-metabolous Characteristics: Enlarged hind legs for jumping. Produce sound (stridulation) by rubbing body parts. Chewing mouthparts. Habitat: Grasslands, fields, forests. Examples : Locusta migratoria (Migratory Locust), Acheta domesticus (House Cricket). Ecological Role: Herbivores and prey for many animals.

25. Hemi-metabolous 06 f. Order: Phasmida (Stick and Leaf Insects) Metamorphosis Type: Hemi-metabolous Characteristics: Excellent camouflage—resemble sticks or leaves. Slow-moving and herbivorous. Wingless or with small wings. Habitat: Forests and vegetation areas. Example: Phyllium giganteum (Leaf Insect). Ecological Role: Plant feeders and prey for birds and reptiles

26. Hemi-metabolous 06 g. Order: Dermaptera (Earwigs) Metamorphosis Type: Hemi-metabolous Characteristics: Elongated body with forceps-like cerci at the rear. Short leathery forewings and membranous hind wings folded underneath. Omnivorous or predatory. Habitat: Moist areas under stones or bark. Example: Forficula auricularia (European Earwig). Ecological Role: Predators of garden pests.

27. Hemi-metabolous 06

28. Hemi-metabolous 06 h. Order: Embioptera (Webspinners) Metamorphosis Type: Hemi-metabolous Characteristics: Small, soft-bodied insects that spin silk from glands on their front legs. Live in silken tunnels or galleries. Females are usually wingless. Habitat: Bark, leaf litter, and rocks. Example : Embia major. Ecological Role : Decomposers and recyclers of organic matter.

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