Kompfner page 2
Larvae and pupae of the wrack dipterans Coelopa vanduzeei (Coelopidae),
Fucellia costalis and F. rufitibia (Anthomyiidae), and Leptocera
johnsoni (Sphaeroceridae) on a California beach.
Helen Kompfner
Hopkins Marine Station of Stanford University
Introduction
The kelp (wrack) flies, Coelopa vanduzeei Cresson (1914), Fucellia
costalis Stein (1910), Fucellia rufitibia Stein (1910), and Leptocera johnsoni
Spuler (1925) are common on California beaches (Cole,1969). The life histories
of such related European species as Fucellia maritima and Coelopa frigida have
been studied (Egglishaw, 1960a and b), but little is known about the immature
forms of the Pacific coast species. Preliminary observations of fly larvae
found living in wrack suggested that a study of distribution and biology of
larvae on the beach would be valuable in further understanding how different
species of flies relate to the wrack, as a food source and habitat. This in¬
vestigation was carried out April-June, 1972, on two pocket beaches of Monterey
Bay, Calif.:(1) the west beach of Mussel Point, Pacific Grove, and (2) the
Point Lucas beach, Pacific Grove. My studies of larvae were accompanied by a
study of the activity patterns and behavior of adult wrack dipterans by another
investigator (Hyatt, 1972) at Mussel Point.
Characteristics of larvae and pupae (Fig. 1 and 2)
The larvae described were collected in the field and raised on samples of
damp wrack kept in the laboratory at room temperature. Initial identifications
were made on the basis of emerged adults. Samples of these adult flies were
examined and identified by Dr.Paul Arnaud of the California Acadamy of Sciences,
Kompfner page 3
and George C. Steyskal of the U.S. Dept. of Agriculture.
Coelopa vanduzeei
Third instar larva. Length 9.0-12.0 mm, greatest width and height 1.5mm
at caudal end, body narrowing anteriorly, second segment 0.5 mm wide. Color
white, with grey ventral spines on abdominal segments. Caudal plates yellow
with black borders, surrounded by pale hairs; 3 spiracles. Anus four-lobed,
located ventro-posteriorly on segment 12. Anterior prothoracic spiracles bi¬
lobed, each'lobe marginally scalloped to form 10 petal-like processes. Anten¬
nae smooth, finely pointed.
Puparium. Length 3.5-6.0 mm; greatest width at segment 8, about half this;
greatest height at segment 8, approximately one third length; ventral surface
and dorsal surface of anterior three segments flattened; dorsum arched; lateral
segment
edges of eachindented; color yellow-brown to brow-black.
Fucellia costalis
Third instar larva. Length 9.0-12.5 mm; body widest at caudal end, 1.5 mm,
tapering to 0.5 mm at anterior end of second segment. Color white, or off-white.
Caudal plates white with three amber spiracles, no caudal plate hairs. Anterior
prothoracic spiracles each with a single cluster of 8-10 lobes. Antennae blunt-
tipped with annular ridges.
Puparium. Length 6.0-7.0 mm, greatest width and height at segments 7 and 8,
3.0 mm. Shape fusiform, circular in cross-section. Color dark reddish browm,
segments 1-11 with wrinkled surface, segment 12 matte.
Fucellia rufitibia
Third instar larva. Length 8.5-10.5 mm, greatest width 1.2 mm, at caudal
end, tapering to 0.3 mm at anterior end of segment 2. Color white, grey at
twelfth segment. Caudal plates white with yellow or red spiracles, no caudal
plate hairs. Anterior prothoracic spiracles each one-lobed, with a single
cluster of 7-11 processes. Antennae blunt-tipped, with annular ridges.
Kompfner page 4
Puparium. Length 4.0-5.0 mm, greatest width and height at segments 7 and 8,
1.5 mm. Shape fusiform, circular in cross-section. Color reddish brown, surface
teture smooth, shiny.
Leptocera johnsoni
Third instar larva. Length 2.0-3.5 mm. Color white, with black spines on
abdominal ridges at anterior end of segments 6-12. Caudal plates on caudal stalks.
plates black surrounded by long, black hydrophobic hairs in tufts of 4 or 5.
Prothoracic spiracles with 5 slender radiating marginal processes.
Puparium. Length 2.0-2.5 mm, width and height greatest at segments 5-11,
0.8 and 0.5 mm, respectively, dorso-ventrally flattened especially segments 1-2
and 12. Color yellow brown, segments 1-4 often translucent. Segment 12 has two
caudal stalks.
Field studies
Distribution of fly larvae was studied on beaches at Mussel Point and Point
Lucas. Samples were taken at high, mid and low sections of the beach. Since
most larvae were found in wrack banks (piles greater than 15 cm in depth, as
defined by Backlund, 1945), vertical distribution within the banks was also
studied. Samples of wrack from various elevations on the beach, and samples
taken at depths of 10,20, and 30 cm within wrack banks, were collected in plastic
bags and returned to the laboratory. Larvae were extracted from the wrack by
shaking the samples vigorously with water, then capturing the smaller larvae
with a fine aquarium net. The wrack sample was then carefully examined for any
remaining larger larvae.
Fig. 3 shows the distribution of fly larvae from wrack banks stranded at
various elevations above mean lower low water. The majority of wrack deposits
at Mussel Point centered around the +3.0 tidal level and consisted of mixed
Kommpfner page 5
red and brown algae and the surf grass Phyllospadix. The major deposits at
Point Lucas consisted of banks of the brown alga Macrocystis concentrated on
the upper beach at tidal heights of 15.0-6.5 feet. Coelopa vanduzeei larvae
were found exclusively in lower beach wrack banks. Fucellia costalis larvae
were found almost exclusively in the upper beach banks. F. rufitibia larvae
were found at all levels, but predominately on the mid and upper beach. L.
johnsoni larvae also occurred widely on the beach but were more evenly distrib-
uted. The occurrence of larvae in wrack corresponds well with the distribution
of the adult flies found on the same beach in studies by Hyatt (1972).
Vertical distribution of fly larvae within wrack banks is shown in Fig.AA.B.
in banks on the lower beach Coelopa vanduzeei predominated in the top 10 cm.
and L.johnsoni at the lowest levels. A small number of F.rufitibia were found,
at levels in
largely in areas between. F.costalis was absent. Observation of a lower
beach bank before and after complete immersion during a high tide showed that
numbers of C.vanduzeei present did not change; numbers of L.johnsoni diminished,
Rowever, suggesting a loss accompanying wave action. In the upper beach bank
(Fig. 48) Fucellia costalis larvae predominated, and F.rufitibia outnumbered
L.johnsoni at the lowest levels. C.vanduzeei was absent. High beach wrack banks
tended to dry out, and as this happened, larger larvae were observed moving down
in wrack over time.
Observations on feeding, behavior, and temporal variation
Larvae appeared to eat the algae on which they were found. Fragments of
Macrocystis were found in the guts of all species. Larvae were never observed
on very fresh wrack; apparently some decomposition must occur before the algae
are eaten. Nematodes were abundant where fly larvae were found and may be in¬
volved in initial algae breakdown, as suggested by Egglishaw (1960B),
Kompfner page 6
Wrack consisting of the kelp Macrocystis seemed to be preferred above other
algae by all larvae collected from natural wrack. When wrack was experimentally
sorted out into separate piles containing only bron algae, only reds, only
Phyllospadix, or a mixture of all typés, and placed on the beach for several
days, larvae were only found on brown and mixed wrack. Larvae placed on red
algae and Phyllospadix died within a day in the lab, while those on Macrocystis
flourished. Those kept without food died within two days, and larvae kept
without moisture died overnight.
Of the four species observed, the larvae of C.vanduzeei and L.johnsoni were
the most active and moved most rapidly.
Over the 5 week period of the study some temporal variation "was observed
in the numbers of C.vanduzeei larvae. In the last two weeks of April none were
found on the beach at Mussel Point. By May 2, they were found in small numbers
and in the week of May 8-15, occurred in multitudes in buried wrack on the lower
beach there and further south along the coast at Pebble Beach and Carmel. The
latter period ooincided with neap tides, and formation of major wrack deposits
on the beaches. By May 17 no more larvae were found and the wrack was also gone
from the beach. Fucellia costalis, F.rufitibia, and Leptocera johnsoni were
found in fairly constant numbers, but never as abundantly as Coelopa vanduzeei
at its peak, over the time interval noted. Some adult L.johnsoni were observed
mating in all wrack deposits observed over 5 weeks.
Laboratory raising of larvae
Attempts to obtain eggs and subsequent larval stages in the laboratory
from captive populations of flies maintained on wrack in large plastic bags
were not successful. However, larvae of the four species collected in the field
were reared successfully on Macrocystis stipes (examined first for foreign larvae
or eggs) in Petri dishes at room temperature. Cultures were wetted and new
Kompfner page 7
Macrocystis added every two days. Pupae were removed, placed in corked vials,
and checked daily for hatching.
The picture of development obtained, while incomplete, provides the be¬
ginning of a timetable for the life history. Data available are shown in Fig.5.
Duration of the third instar was shortest in Coelopa vanduzeei, longest
in Fucellia costalis. The former lives lowest in the intertidal zone, the latter
highest on the beach. Duration of pupal period showed considerable variation
among species and within C.vanduzeei. For the latter, there may be some connection
between intertidal height on the beach and length of pupal period. Although
later development took place in the laboratory, the 12 individuals of C.vanduzeei
which hatched after a 4 day pupal period were collected from buried wrack at the
13.0 foot tide level, while the individual which spent 9 days as a pupa was
taken from an upper beach wrack bank. L.johnsoni had a pupal period of 6-7 days,
F.rufitibia and F.costalis 12-15 days. F.costalis larvae may remain in the third
instar for considerable periods; one batch of 10 remained in this stage for 25
days before pupation.
Discussion
The flies appear to use different strategies in exploiting the available
food and habitat resources for larvae on the beach. C.vanduzeei is found almost
exclusively in lower beach wrack which is wetted at least once a day and seldom
remains on the beach longer than two weeks. The main pressure here is for quick
larval development and a short pupal period. The caudal plate hairs allow the
larva to breathe from air bubbles trapped in the wrack during periods of tidal
immersion. Immature F.costalis and F.rufitibia, found mainly on the mid and
upper beach levels, are able to use wrack for longer periods. Caudal hairs
are lacking. The danger of being washed out to sea is less than that of
desiccation. The pupal period reflects this, being relatively long. L.johnsoni
Kompfner page 8
larvae are found in large numbers and are distributed both high and low on the
beach. Their caudal plate hairs allow them to respire when submerged in wrack
beds low on the beach, but their small size makes them vulnerable both to being
swept out of low immersed wrack, and to desiccation in higher beach wrack.
Perhaps this is why L.johnsoni tends to occur well below the surface of wrack
banks. A comparison of mean tidal height of distribution and mean pupal period
for each species suggests that species found higher on the beach may have longer
pupal periods, although the variation within each species is large enough to
eliminate meaningful statistical comparison with present data.
Sumary
Larvae and pupae of Coelopa vanduzeei, Fucellia costalis, Fucellia rufitibia,
and Leptocera johnsoni were studied on two California beaches. Third instar
laryae and puparia are described. Studies of distribution of larvae on the beach
showed C.vanduzeei occupies lower beach wrack banks and F.costalis the upper
beach banks. F.rufitibia larvae, while widespread, occur more in mid and upper
beach wrack, while those of L.johnsoni are found at all levels. Larvae were
observed to prefer the kelp Macrocystis both as a habitat and food source.
C.vanduzeei larvae were observed in large numbers only during a two week period
coinciding with a major wrack deposit. F.costalis, F.rufitibia, and L.johnsoni
were found in constant numbers over 5 weeks. Duration of pupal periods in the
laboratory were: C.vanduzeei, 4-9 days; L.johnsoni, 6-7 days; F.costalis and
F.rufitibia 12-15 days. Average duration of the pupal period appears to increase
with increasing tidal height of the larval habitat.
Acknowledgements
I would like to thank Dr. Paul Arnaud of Calif. Acad. of Sciences and
George C. Steykskal of the U.S.Dept. of Agriculture for identifying the adult
Kompfner page 9
flies of this study. Also Joel Hyatt, for many helpful discussions about flies
and larvae on the beach. I am expecially indebted to Dr. Donald P.Abbott of
Hopkins Marine Station, for his unfailing patience and encouragement with this
study and the editing of this manuscript. Dr. I.A.Abbott also provided much
appreciated encouragement during this study.
Literature cited
ecology and chorology. Opuscula Entomol.
Backlund, H.O. 1945. Wrack fauna of Sweden and Finland, Lund, Sweden, suppl, 5:1-238.
Cole, F.R. 1969. The flies of Western North America. Univ. of Cal. Press.
Berkeley, Cal.
Egglishaw, H. 1960a. The life history of Fucellia maritima (Haliday) (Diptera,
Muscid.) Entomologist. Nov.1960,p.225-231.
1960b. Studies on the family Coelopidae (Diptera). Trans.R.Ent.Soc. 112:109-140.
Hyatt, Joel, 1972. Behavior of wrack dipterans, F.rufitibia (Anthomyiidae) and
C.vanduzeei (Coelopidae) on a California beach. Unpub. MS on file at Hopkins
Marine Station Library.
Kompfner page 10
Figure captions
Figure 1. A.Coelopa yanduzeei B.Fucellia costalis C.Fucellia rufitibia D.Leptocera
third instar
johnsoni. (1) left lateral view of mouthparts (2) left lateral view of entire o
larva (3) caudal view, showing caudal plates and posterior spiracles.
Figure 2. Puparia, dorsal views. A)Coelopa vanduzeei, B) Fucellia costalis,
C)Fucellia rufitibia D) Leptocera johnsoni.
Figure 3. Distribution of larvae on beach with tidal height.
Figure 4. A)Vertical distribution of larvae in lower beach wrack bank.
B)Vertical distribution of larvae in upper beach wrack bank.
Figure 5. Developmental periods of lab raised larvae.
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