Diptera: Mycetophilidae) by William G

THE NATURAL HISTORY OF THE FUNGUS GNATS LEPTOMORPHU8 BIFASCIA TUS (SAY) AND L. SUBCAERULEUS (COQUILLETT) (DIPTERA: MYCETOPHILIDAE) BY WILLIAM G. EBERHARD Museum of Comparative Zoology, Harvard University" Although there are many species of Mycetophilidae (or Fungi- voridae) and some that are quite common, little is known about the natural history of most species. The literature on the genus Lepto- rnorphus is typically scanty" there are no descriptions of any activities of adults, and only brief descriptions of the general habitat and activities of eggs, larvae, and pupae of one species, L. walkeri (Edwards 1925, Brocher I93I, Madwar 937). This report, which includes observations on all life stages of Leptomorphus bifasciatus and L. subcaeruleus, is the first study of the natural history of these species. Most of the observations were made during the summer of 968 near Rensselaerville, N.Y., at the E. N. Huyck Preserve, and a few additional notes were made on individuals ound near West Chester- field, New Hampshire. Leptomor'phus subcaeruleus was found near West Chesterfield, and both this species and L. bifasciatus (with L. subcaeruleus most common) occurred on the Huyck Preserve. I discerned no difference in the habits of the two species, and adult males and emales of both species were found at the same time at several sites in the Huyck Preserve. Specimens of larvae, pupae, and adults of both species have been deposited in the Museum of Com- parative Zoology in Cambridge, Massachusetts. 1I am grateful to the directors and staff of the E. N. Huyck Preserve for generously supporting a summer of research, and to Dr. R. Dalgleish for help in obtaining financial support for publication of this paper. I am also indebted to Dr. R. Gagn6 for identifying adult specimens, Dr. F. Shaw for useful advice, and Dr. M. Gordon for supplying culture media. My wife Mary Jane has offered valuable help with all stages of this study. Photo- gr.aphie supplies were furnished by Harvard University. Present address Depto. Biologia, Universidad del Valle, Call, Colombia. Manuscript received by the editor September 25, 1970. 362 Psyche [September Precopulatory behavior of males Male flies searched out female pupae which were suspended on silk threads, then hung under them (Fig. until the adult emerged. They flew in a characteristic bobbing pattern as they searched or pupae hanging under the bottom surfaces of logs. Usually, as they flew along the length of the log, they bobbed up until they hit the bottom of the log with their front legs, which they carried raised over their heads, then flew down and onward. Sometimes they swung back and forth from one side of the log to the other as they flew along under it. They made frequent darting flights to other objects in the vicinity where they occasionally landed and paused. Although the bouncing flight appeared erratic, the pattern is probably controlled. A male which was confined in a. cage which had pupae fastened to the roof with long pins was able to touch pupae over and over without running into pins. The males' responses to pupae they encountered are listed below in order of increasing attention to the pupa. I. no change in flight pattern :. hover near pupa monmentarily, back off 3. (often preceded by hovering) touch pupa, back off 4. touch pupa, stop flying and cling to it, move about under it, fly off 5. same as 4 except end by hanging immobile under pupa with ventral side of thorax pressed against the dorsal surface of the pupal thorax (Fig. Encounters with a given pupa did not always elicit the same reaction, even from the same male. The males probably used either visual cues or tactile cues from their front legs (or both) while locating pupae during bobbing flight. The males usually mounted a pupa with their anterior ends at the pupa's anterior end and their longitudinal axes parallel to that of the pupa. Without exception, the anterior end of a pupa hung below the rest of its body, and this position appeared to be the cue used by male; in positioning themselves: a pupa which was hung so the posterior end was the lowest was repeatedly mounted backwards. Males hung persistently only under pupae of females about to It is possible that the males were actually responding to pharate adults still within the pupal cuticle rather than to actual pupae. Observations were not made on this point, so the term "pupa" below should not be construed to exclude this possibility. 197o] Eberhard--- Fungus Gnats 363 Fig. 1. A male L. subcaeruleus clinging to a pupa. emerge. Only five of more than 40 pupae observed in nature had males hanging under them. All five of these pupae were emales, and four o them produced adults within one day (the average pupal lie is about our days). The fith died. Males oten mounted young or male pupae again and again only to. climb off each time, but seldom dismounted from mature female pupae. Males also con- sistently ignored some unsuitable pupae but repeatedly touched and mounted other unsuitable pupae nearby. There was brisk competition among males for suitable pupae. Males flying near a male hanging under a pupa often bumped against the resident male as they flew by; three extended fights over pupae were observed; and an additional male was found hanging on the back of a newly emerged female which was mating with another male. In each of two fights observed from the beginning, one male 364 Psyche [September was hanging immobile under a pupa and a second male approached, bumped against the resident male, and clung to the pupa. Both males held the pupa or the pupal thread with their ront and middle legs, and buzzed their wings and pushed each other with their hind legs and abdomens. Each male appeared to be attempting to dislodge the other. Two o the tights ended when both males ell from the pupa, separated, and flew away; the other ended when the intruder, which was smaller than the resident, let. Although combatants let the pupa when they were dislodged, they sometimes remained in the vicinity. One defeated male rested on a lea about one meter rom the pupa or about a minute, then hung under a pupa about 20 cm rom the first, jkno,ther contested pupa was revisited within 15 minutes by a male o the same size and color pattern as one o the contestants. After another suspected ([ght (two males flew rom the vicinity o a single pupa as I approached), males of the .same sizes and color patterns as the fleeing males reappeared within 15 minutes, and one of them spent more than an hour flying in the vicinity in an apparent search for the pupa. This pupa was in a spot particularly difficult or a male flying in normal searching patterns to reach. Mating Complete mating sequences were observed twice, once in nature when a waiting male mated with a emale emerging from her pupal skin, and once in captivity when both animals were 1ying in a cage. In the first case, the emale's thorax and head (the lowest parts o her body) were cradled against the ventral surfaces of the male's thorax and coxae as she emerged from her pupal skin, and he main- tained this contact by lowering his body as she emerged. _As she came free from the skin, the female drew her legs free from the pupal cuticle, then extended them perpendicular to her body axis just as other emerging adults did (below). However, in contrast to others, her abdomen came completely free from the pupal cuticle very quickly, and for a moment she lay just above the male, their bodies both horizontal. Almost immediately he curled the tip of his abdomen over the tip o hers (he had curled his over the tips o her wings twice before her abdomen emerged) and pressed it against the ventral surface o t'he tip o her abdomen, then lowered his abdomen until they were both nearly vertical, and gently turned her I8o on her longitudinal axis with his legs. This brought her legs against his legs and the pupal skin, and she clung to them weakly. Both animals remained nearly motionless in this position (Fig. 2) 1970] Eberhard Fungus Gnats 365 for about three hour.s. Then after a tew twitches by the female, they separated, and both hung or several moments under the pupal skin. The other observed mating involved two individuals placed in a cage after being captured in copulo under a pupal skin and then kept separated for several ho.urs. In the course of several minutes of flying around the cage, the male brushed against the temale several times as she sat on the floor, and each time she started and moved away. One time, however, she did not move away when the male landed on her back. He immediately curled the tip of his abdomen over hers, engaged it against the ventral surface of the tip of hers, and then dismounted and turned 8o to ace away from her. They both rested on the floor for over an hour, then separated. On another occasion a male attempted to mate with another female (a virgin) in the .same situation, but was unsuccessful. Although she allowed him to land on her back, she did not let him press the tip of his abdomen against the ventral surface of hers" whenever he curled the tip of his abdomen over hers, she moved her abdomen to the side or pressed it against the surface she was on.

Load more