1. Biology of Dicosmoecus gilvipes in Northern California Streams
Vincent H. Resh, Morgan Hannaford, John Jackson, and Patina Mendez
Department of Environmental Science Policy & Management
University of California, Berkeley
Today I will be talking about long-term studies that we have done on the limnephilid caddisfly Dicosmoecus gilvipes in Northern California streams
Vince sends you his regards and is sorry that he can’t be here at the meeting today.

2. Dicosmoecus gilvipes (Hagen)
Occurs from Northern California to British Columbia and east to Montana, Nevada, Idaho and Wyoming
Large size, high densities, synchronous emergence make it important in trout diets
To anglers it’s the
“Giant Orange sedge”, “October Caddis”
D. Gilvipes is distributed throughout the western US and is extremely important to anglers as a food for trout

3. Study Sites in Northern California
McCloud River —larval behavior
Eel River —phenology and grazing studies
Big Sulphur Creek —adult behavior
Our studies have been concentrated in three main streams

4. Egg Masses Found at the base of Carex sedges
Not found on leaves overhanging streams as reported for some other Dicosmoecinae (after hundreds of hours of searching)
Unlike other reports of life history studies of Dicosmoecus, we do not find the eggs attached to overhanging vegetation in spit of hundreds of hours of searching these expected oviposition sites. Instead we find them atttached to Carex stems ?

5. Among first benthic macroinvertebrates to colonize storm-scoured, mid-channel areas
Predominantly scrapers-grazers: gut content contain diatoms, filamentous algae, and some mineral particles
Densities larvae/m2
Read text
Density is high considering the size of these organisms

6. Larval Cases
Early-instar cases made from organic material and detritus
With 3rd instar, some pebbles incorporated, a time when discharge begins to recede (except in snow-melt streams)
4th instar increases stone material in case; 5th instar cases entirely made of stones (30mm in length)
Cases change over larval development from organic matter, to a mixture of organic and mineral matter, to mineral particles. This may be tied to life cyle phenology and availability of material, and hydrologica conditions present during development

7. Larval Biology Larvae are highly mobile moving up to 25 m/day
Because of it’s large size we have been able to tag individual larvae and follow their movement patterns. Each of those series of lines represent one individual, and the graphs indicate different distances moved by individuals. There are no significant upstream or downstream movement or turn angles.
Patterns of movement of D. gilvipes follow a random-walk model except large larvae move farther than smaller larvae, and there is a pronounced diel rhythm to movement (traveling faster during the day) (
2/3 of time budget spent in feeding
Larvae feed in areas with more food, and minimize “turn angle”, reducing possibility that they return to a recently grazed patch
In some streams, larvae may compete exploitatively for food
From Hart and Resh 1980

8. Temperature influences on Development
Average accumulated degree days (>0 C) to reach fifth instar:
Upstream-most site, 2,485 degree days
4 km downstream, 2,585 degree days
D. gilvipes at downstream site reach 5th instar and diapause 2 weeks earlier than at upstream site
D. gilvipes is rare below the downstream site, perhaps reflecting temperature tolerance

9. Developmental Diapause and Pupation
5th instars attach cases to undersides of boulders and remain dormant until pupation
Diapause lasts one month, followed by pupation
Pharate adults emerge from cases on underside of boulders and crawl to shore in late afternoon
Just read

10. Adults Adult flight and mating occur in early evening
Pheromone-based mating system (Resh et al. 1987; Jackson and Resh 1991)
Live females of D. gilvipes attract males during the night with 58% being captured within 1 hr after sunset
Timing of male response to female pheromone was the same as male response to live females
Males and females fly during periods of mate attraction but not generally at other times
Males but not female of D. gilvipes exhibit circadian rhythms
The brief but coordinated activities may contribute to both reproductive success and reproductive isolation
Pheromones are produced by paired exocrine glands located on 5th sternite

11. Life Cycle in the Eel River
In California streams, D. gilvipes exhibits a univoltine life cycle
In Flathead River in Montana, 2-yr cycle was found by Hauer & Stanford 1982
1st instars appear in spring and grow through summer, overwintering as 5th instars in apparent diapause
5th instars are active again when temp >1C, and then enter 4-6 wk prepupal diapause, emerging August to October

12. Interactions With Other Organisms—Study Design
m2 cylinder cages used
Exclusion of D. gilvipes
Enclosures (40 D. dilvipes/m2)
Ambient density controls (allowed D. gilvipes access to cages)
Ambient densities were also measured to assess effect of cages on providing D. gilvipes access
I now want to talk about an experimental study on the interaction of Dicosmoecus gilviped with other organisms.
The experimental design involved both enclosures containing D. gilvipes and exclosures (where D. gilvipes was excluded)

13. Number of Sessile Organisms at Different Densities of D. gilvipes
Biotic Interactions
Number of Sessile Organisms at Different Densities of D. gilvipes
Fewer sessile invertebrates colonized D. gilvipes enclosures than either in exclosures or controls
A negative correlation (p,0.001) existed between densities of active D. gilvipes and densities of sessile organisms
Read text
Common sessile taxa: Tinodes, Petrophila, Antocha, Cricotopus, Polycentropus, Tanytarsus, Simulium

14. Biotic Interaction Involves Direct Interference with Sessile Grazers
30x15 cm boxes stocked with cobbles containing Tinodes (a psychomyiid caddisfly) larvae and tube cases
2 D. gilvipes larvae added to each box
% occupancy of tubes before and after addition used to determine effect of addition
In a second study we examined the effects of D. gilvipes on the numerical dominant algal feeder in this stream—Tinodes
% occupancy of tubes before and after addition used to determine effect of addition of D. gilvipes

15. Biotic Interaction Involves Direct Interference with Sessile Grazers
37% of Tinodes tubes damaged, and 2 of 10 D. gilvipes contained Tinodes body parts
The grazer is also a predator!
Read text
Others have noticed this predatory behavior of this species

16. Study Conclusions
D. gilvipes functions as a “keystone species” in the Eel River, affecting density and composition of sessile macroinvertebrates
Removal of D. gilvipes causes the community to change composition
A keystone species is a species whose removal affects the composition of the community. Our studies suggest that in the Eel river D. gilvipes is cclearly a keystone species

17. Oddest Relationship
D. gilvipes may transmit trematode worms that when ingested by horses and cause Potomac Horse Fever (Madigan et al. 2000)
Horses were fed insects infected with metacercaria; D. gilvipes infected horses
The parasite is maintained in aquatic ecosystems and can occur in horses through accidental ingestion of Dicosmoecus!
In a study of parasite transmission to horses, D. gilvipes was the only insect that resulted in disease transmission to horses!

18. Thank you!

20. Behavioral Studies in the Laboratory
Time spent in feeding, crawling, resting, and case building varied among 3rd, 4th, and 5th instars (Li and Gregory 1989)
Larvae feed ½ time, 3rd instars fed longer on diatoms, 4th instars longer on filamentous algae
4th instars spend most time case building; 5th instars resting
Neither aggression nor cannibalism were observed

21. Dicosmoecus gilvipes as Grazers: Laboratory Studies
D. gilvipes drastically reduced periphyton biomass and resulted in a shift to a blue green algae community (Walton et al. 1995) and grazed entire substrates cf. the patchy feeding of Juga snails or Baetis mayflies (Dennicola et al. 1990)
D gilvipes doesn’t completely remove algal assemblage but changes growth form and algal assemblage physiognamy (Steinman et al. 1987)
D. gilvipes grazing effects was higher than Juga snails or Baetis mayflies (Lamberti et al. 1987, 1992, 1995)
Growth of D. gilvipes is density dependant and highest at its lowest densities (Lamberti et al. 1995)
D. gilvipes has high growth rates but low efficiency in resource use (cf. Juga)
Different life history strategies may explain coexistence of different grazers Juga and D. gilvipes

22. Dicosmoecus gilvipes as Prey
In late June and July, D. gilvipes are 80% of Harlequin ducks (Histrionicus histrionicus) diets (in Oregon, Wright et al. 2000)
After a severe flood, numbers of D. gilvipes were reduced and numbers of harlequin duck numbers were reduced and brood development was delayed
D. gilvipes make up a significant component of American dipper (Cinclus mexicanus) and D. gilvipes inhabit deeper pools in response to dipper predation (in Utah, Hart and Marti 1993; in California, Teague et al 1985)
Human recreational activities effect early instars more than later instars of D. gilvipes (in Oregon, Wright and Li 1998)
D. gilvipes may transmit trematodes that when ingested by horses cause Potomac Horse Fever (Madigan et al. 2000)

23. Mediterranean Climates Can Influence Results of Field Experiments
18 yrs of field observations and 5 yrs of experiments in the Eel River, California, by Mary Power
Inferences about food webs differ during flood and drought years
Number of trophic levels connecting algal biomass to consumers differ in a given year
Strong biotic interactions differ in a given year
Behavioral trophic cascades differ in a given year

24. Why Do Food Webs Differ Year-to-Year?
Cladophora algal or diatom blooms are basis of food chain
Trout suppress grazing insect populations during years with floods and algae increase
BUT if drought occurs, D. gilvipes are more abundant and Cladophora biomass is lower
Slides of Cladophora, diatoms, steelhead, dicosmoecus, Baetis

25. Power et al. 2008, Ecological Monographs

26. D. Gilvipes Substrate relationships
Sediment size has significant effects on D. gilvipes survival; 3rd instar more sensitive than 5th instars most (Parker et al. 2002)
D. gilvipes show that sampling efficiency can be optimized because non-aggregated spatial distribution patterns can occur in uniform substrate patches (Lamberti and Resh 1979)
This study underscored the value of habitat stratification