Class meeting: October 19th Stick insects, web spinners and angel insects

1. Class meeting: October 19th Stick insects, web spinners and angel insects

2. Stick insects, web spinners and angel insects • (EE, pp. 129-138)

3. Phylogeny of Hexapoda from p. 52 Phasmatodea Embioptera or Embiidina Zoraptera

4. Phasmatodea Common name: Stick and leaf insects, walking sticks (2,500 known world species (0.25%)) Derivation: Gk. phasma - apparition, spectre Size: Body length up to 300 mm; mostly 10-100 mm Metamorphosis: Incomplete (egg, nymph, adult) Distribution: Mainly tropical and subtropical Number of families: 3

5. Embioptera or Embiidina Common name: Web spinners (200 known world species (0.02%)) Derivation: Gk. embios - having life; pteron - a wing Size: Body length up to 300 mm; mostly 10-100 mm Metamorphosis: Incomplete (egg, nymph, adult) Distribution: Mainly tropical; some in warm temperate regions Number of families: 8

6. Zoraptera Common name: Angel insects (30 known species (0.003%)) Derivation: Gk. zoros - pure; a+pteron - wingless Size: Body length 2-3 mm Metamorphosis: Incomplete (egg, nymph, adult) Distribution: Mainly tropical, some warm temperate regions Number of families: 1

7. Key Features • slender, stick-like or broad, leaf-like body with widely-spaced legs • slow moving and herbivorous • confined to vegetation, which many mimic

9. Phasmatodea(crypsis in stick and leaf insects) • freeze motionless when disturbed • holding the middle and hind legs tightly along the body, stretching the front legs out • some sway gently, mimicking the movements of the vegetation

10. The Leaf Insects(50 species - all in the family Phylliidae) Common features: • broad and flattened, brown or green, with leaf-like expansions on all leg and body segments • only found in south-east Asia, New Guinea and Australia

11. The Stick Insects(the great majority (~ 98%) of the Phasmatodea are stick insects) Common features: • body form can be variable • short and smooth • large and very spinny

12. The stick insects(the great majority (~ 98%) of the Phasmatodea are stick insects) Common features: • the head is often characteristically domed, with long, thread-like antennae • chewing mouthparts, with laterally placed compound eyes

13. The stick insects(the great majority (~ 98%) of the Phasmatodea are stick insects) Common features: • front wings are short, toughed and, at rest, slightly overlapped to protect the much larger fan-shaped, membranous hind wings • many species have short hind wings (or no wings at all)

14. The stick insects(males are generally smaller than females & have one less molt) Common features: • males likely attracted by pheromones, and mount on top (sometimes for many days) • parthenogenesis is common in some stick insects, and in some species males are very rare or even unknown

15. Stick insect eggs(made to look like seeds in size, surface texture, color and shape) • glued to leaf surface or dropped on the ground • eggs are often carried back to ant’s nests - safe from herbivores and parasitic wasps capitulum - mimics elaiosomes of higher plants

16. Defense in stick insects(alternatives to standing still) • autotomy - the dropping of legs • partially regenerated through subsequent molts • a fracture line at the base of the legs, between the femur and trochanter • special diaphragm seals off the wound rapidly to prevent loss of body fluid

17. Damage(most aren’t serious pests - but some occasionally are) • Australian spur-legged phasmid (Didymuria violescens) defoliates highland Eucalyptus forests • even in Texas, some species can cause problems Megaphasma dentricus

18. Key Features • gregarious in silk galleries (protection, desiccation) • swollen first tarsal segment contains silk glands

19. What do they eat? • dead plant material, litter, lichens and moss • but adult males do not feed; jaws instead are used to grasp the female while copulating

20. What about the silk?(how do they make it?) • both sexes produce it, from numerous silk glands located in the swollen basal tarsal segment • it passes through hair-like or bristle-like silk ejectors on the ventral surface • as the front feet are rubbed against the substrate, silk strands are pulled from the ends of each ejector to form a mat of silk

21. What about the silk?(what is it used for?) • they live in it, and it provides protection • but still attacked by ants and parasitic wasps • some specialist bugs suck out the eggs, and dead or dying larvae and adults • some specialist ectoparasitic wasps • females lay eggs in the silk galleries and build a protective nest over their eggs • females stay near their eggs, and when eggs hatch they have to break open the nest to release the newly hatched first instars • some species exhibit maternal care - provide a paste of masticated food)

22. Key Features • small and delicate - look like minute termites • some morphological characters suggest they are an early offshoot from ancestors of cockroaches • they possess... • short abdominal cerci • downward-pointing mouthparts

23. Adults are dimorphic, either... • blind, pale and wingless (resembling the nymphs) • darkly pigmented with eyes, ocelli and two pairs of sparsely-veined wings

24. Zoraptera(angel insects) • first members discovered in the early 1900’s • they are gregarious under bark, in piles of wood dust, or in leaf litter • they eat fungal threads, spores, mites and other small arthropods

25. Zoraptera(angel insects) • winged morphs disperse to new locations and the wings are then shed • what about courtship? • elaborate pre-copulatory behavior • males give females gift secretions (from cephalic gland) to induce females to accept them as mates • females can judge quality of the gift and will terminate copulation prior to sperm transfer if the male is inferior • mating success is determined by age, and dominate males get three-quaters of all matings