Aquatic Insects

1. Aquatic Insects 8 April 2009

2. Aquatic Insects • Insecta (even Hexapoda) are plesiomorphically terrestrial. • But there have been numerous colonizations of the freshwater aquatic environment. • Far fewer colonizations of marine aquatic environment.

3. Hemimetabolous Aquatic Insects • Some lineages have almost* exclusively aquatic naiads. • Ephemeroptera • Odonata* • Plecoptera (the only aquatic Polyneoptera) • All of these have terrestrial adults.

4. Hemimetabolous Aquatic Insects • There are multiple colonizations of aquatic environments by Heteroptera. • Most of these are also aquatic as adults.

5. Holometabolous Aquatic Insects • Colonized aquatic environments much more recently. • Numerous colonizations within numerous orders • Only two have exclusively* aquatic larvae. • Only some Coleoptera remain aquatic as adults.

6. Holometabolous Aquatic Insects • Neuroptera: One lineage (Sisyridae, spongillaflies). • Coleoptera: Numerous colonizations throughout. • Diptera: Numerous colonizations, especially in Nematocera. • Lepidoptera: Numerous origins, but NOT common

7. Habitats for aquatic insects • Lotic: flowing water • Influenced strongly by velocity of flow • Particle size • Substrate type • Inputs from outside and local nutrient supplies • Lentic: standing water • Often strong zonation • Limnetic zone- penetrated by light • Profundal zone- deeper zone w/o much light

8. Unusual Habitats • Marine environments • Intertidal habitats • Between high and low tide • biting flies, plant feeding insects, detritivores • Littoral habitats • Coastal regions with shallow water • Some midges and beetles • Open ocean: water striders feeding on food of terrestrial origin • RARE! WHY???

9. Unusual Habitats • Temporal water bodies (e.g. vernal pools) • Common in areas with seasonal rainfalls • Numerous adaptations • Ability to find ephemeral pools (meteorological cues?) • Desiccation resistant diapause • Very common as eggs • Some with ability to undergo numerous dehydrate/rehydrate cycles: anhydrobiosis • Plant container habitats: Phytotelmata

10. Oxygen Supplies • Air: 200,000 ppm (20%) • Lotic environments (15 ppm) • Depends on O2 production/consumption by plants • Affected by turbulence and water quality • Lentic environments • Oxygen levels vary with temperature, salinity, and depth • Turbulence affects nutrient and oxygen distribution • Anoxic • No oxygen present

11. How do aquatic insects obtain oxygen? • Atmospheric oxygen • Keep part of body out of water • Carry oxygen into water • Aqueous oxygen • Use of open tracheal system • Adult insects • Immature forms • Use of closed tracheal system • Specialized structures for gas exchange in water • Often adults have open tracheal system

12. Tracheal System

13. Closed Tracheal System • Gills- lamellar extensions of tracheal system • Found in many insect orders • Gills may be in many places • Base of legs • Abdomen • End of abdomen • How is this analogous to insect ears?

14. Open tracheal system in flies • Respiratory siphons near abdomen or thorax • Different location in mosquito pupa than larva

15. Open tracheal system in diving beetles • Bubble stored beneath elytra • Gas exchange can occur in water Does the bubble increase linearly with oxygen consumption? What happens to the exhalation product?

16. Other air bubble gills • Water kept away from body through ‘hairs’ or ‘mesh’ • Oxygen diffuses from water to air against body • Usually slow moving insects with low oxygen demand

17. Lotic Adaptations • Flattened bodies • Attachment through suckers Water pennies (Coleoptera: Psephenidae) Net-winged midges (Diptera: Blephariceridae

18. More Lotic Adaptations • Nets & Cases Trichoptera net Trichoptera cases

19. Lentic Adaptations Water Strider (Gerridae) • Taking advantage of surface tension of still water Whirligig Beetle (Gyrinidae)

20. Adaptations to nearly anoxic environments • Hemoglobins • Many larval chironomid midges (Diptera) = bloodworms • Some notonectid bugs (Heteroptera) = backswimmers • Very, very high affinity for oxygen (unlike us) • Only downloads when oxygen concentrations in tissues decrease, not when tissues become acidic

21. Using insects to monitor aquatic environments • Usefulness • Diverse taxa to choose from, many common • Functionally important to ecological community • Ease of sampling many individuals without major ethical constraints • Ability to identify species • Responses • Increases of certain taxa in waters with sediment, low • Oxygen, increases in temperature • Loss of diversity with pollution and or eutrophication

22. Ephemeroptera • Naiads often with abdominal gills • Also maxillary and labial gills! • Generally 3 styli on naiads and adults. • As many as 45 instars • Anything else?

23. Odonata • Dragonflies & Damselflies • Rectal/anal internal gills. • Caudal lamellae also serve as gills. • Up to 20 instars. • Predators as naiads and adults.

24. Plecoptera • Mostly temperate regions • 10-33 instars • Closed tracheal system with anal gills. • Need high oxygen, good environmental indicators.

25. Hemiptera: True Bugs Notonectidae: Backswimmers • Diving or at surface • Adults and naiads both aquatic. • Highly modified legs. • Generally wings still functional as adults, can disperse between waterways. Corixidae: Water Boatmen Naucoridae: Creeping water bugs Gerridae: Water striders

26. Hemiptera • Left: Nepidae (water scorpions) tails are breathing tubes • Right: Belostomatidae (toe-biters) egg tending by males

27. Trichoptera • Case & net makers. • Abdominal tracheal gills.

28. Coleoptera • Aquatic larvae, aquatic adults • Aquatic larvae, terrestrial adults • Terrestrial larvae, aquatic adults • Pretty much all pupate on land

29. Diptera • Often with anal spiracles breathing at surface • Very diverse • Almost all disease vectoring Diptera have aquatic larvae (?)

30. Megaloptera & Neuroptera