Aquatic insect populations in transplanted and natural populations of the purple pitcher plant, Sarracenia purpurea, on Prince Edward Island, Canada

In early July 1991, 234 pitcher plants (Sarracenia purpurea) were transplanted from a Prince Edward Island bog being mined for peat into three bogs that varied with respect to previous pitcher plant abundance. One bog had a thriving natural pitcher plant population prior to transplant, while the other two had fewer than three pitcher plants. Between mid-June and late August 1993, abundances of the pitcher plant inquilines Wyeomyia smithii (Diptera: Culicidae), Metriocnemus knabi (Diptera: Chironomidae) and an unidentified sarcophagid fly (Diptera: Sarcophagidae) from transplant bogs were compared with remaining populations in the source bog and with other natural populations. Of the three inquilines, W. smithii was the most severely affected by transplant; it was extremely rare or absent in transplanted pitchers, although it was found in all other bogs investigated on Prince Edward Island. Metriocnemus knabi larvae were common in all bogs investigated, except for those transplant bogs where pitcher plants were rare prior to transplant. Sarcophagid larvae were found in all of the bogs sampled, and were apparently unaffected by transplant. Desiccation during the transplant process, as well as the time of the transplant, may play a role in the success of recolonization of the pitcher plants after transplanting.

EFFECTS OF FENITROTHION INSECTICIDE ON INHABITANTS OF LEAVES OF THE PITCHER PLANT, SARRACENIA PURPUREA L.

By injecting fenitrothion into fluid in leaves of pitcher plants, Sarracenia purpurea L., it was determined that the mosquito, Wyeomyia smithii (Coquillett), and the midge, Metriocnemus knabi (Coquillett), are under some risk from fenitrothion forest sprays at the rate of 210 g AI/ha. Wyeomyia smithii is slightly more susceptible than is M. knabi. Other leaf inhabitants, mites and rotifers, were not affected by initial concentrations of fenitrothion in the fluid (up to 9.6 μg/L) that did affect the mosquito and the midge.

CHIRONOMIDAE (DIPTERA) OF PEATLANDS AND MARSHES IN CANADA

A survey of the literature has revealed that the Chironomidae are one of the most abundant and diverse groups of insects present in Canadian peatlands and marshes. A total of 104 named species of Chironomidae has been recorded from Canadian bogs, fens, and marshes. At least 207 species are present if all unnamed species are included in the total. However, until more information is available about the distribution of chironomid species, particularly those from fens, it is not possible to determine if any species (other than Metriocnemus knabi Coq.) are restricted to these habitats. Although several studies have been conducted in marshes and bog pools, the saturated peat habitats of fens and bogs have been little studied.Most information on chironomids within peatlands and marshes is based on emergence trapping of adults, and there have been few attempts to study the ecologically important immature stages. Several aspects of chironomid ecology pertinent to peatlands and marshes are presented, based primarily on information gathered from other shallow-water habitats. The ecological and economic importance of chironomids within these habitats remains largely unknown. Most effort to date has been expended on faunal surveys, and any attempt to study chironomid ecology within peatlands and marshes would add greatly to existing knowledge.

Seasonal dynamics and ecological strategies of the pitcher plant chironomid, Metriocnemus knabi Coq. (Diptera: Chironomidae), in southeast New Brunswick

In southeast New Brunswick the chironomid, Metriocnemus knabi, an inhabitant of the aquatic system contained within the leaves of the pitcher plant, Sarracenia purpurea, show seasonal fluctuations in numbers related to emergence and colonization, but density is usually correlated with the potential volume of the leaves. Females from a May emergence oviposit into overwintered leaves and produce a generation which emerges in August prior to the deterioration of the leaves. The progeny of the August emergence develop in leaves of the current summer growth and do not emerge until the following July. Ovipositing by this generation can be into overwintered or newly opened leaves. Larvae that begin development in overwintered leaves, which show progressive deterioration during the later summer and autumn, migrate to younger leaves that have not achieved complete colonization. The July emergence produces the generation which emerges the following May. Thus, there appears to be two cohorts in the population, each of which produces three generations every 2 years. This unusual life cycle tends towards maximizing use of the living habitat which also has a seasonal pattern of growth and senescence.

Oxygen–fauna relationships in the pitcher plant Sarracenia purpurea L. with reference to the chironomid Metriocnemus knabi Coq.

The aquatic habitat contained within the leaf of the pitcher plant Sarracenia purpurea has a dissolved oxygen concentration consistently in excess of 77% saturation in spite of a high community respiration rate. The oxygen concentration is maintained primarily by diffusion through the wall of the sarcophagus and is not affected by plant photosynthesis. Because of the consistently high oxygen concentrations, the inquiline Metriocnemus knabi is not tolerant of lowered oxygen concentrations as it is adapted to a habitat with a consistently high oxygen concentration.

Determining dry weight and percentage dry matter of chironomid larvae

Reproducible live wet weights may be obtained for medium to large larvae of Metriocnemus knabi and Chironomus attenuatus after blotting them on filter paper for 1 min. To obtain reliable measures of wet weight for smaller larvae the blotting time must be reduced in proportion to the surface area/volume ratio of the larvae. Dry weights are easily obtained by oven drying at 60 °C for 24 h but drying for several days does not affect the results. A temperature of 100 °C decreases die percentage dry matter in C. attenuatus. Both species display an increase in percentage dry matter with increasing size. The extent to which the gut is filled with food has no effect on the percentage dry matter. Attempts to determine dry weight directly from preserved larvae were unsuccessful.

Overwintering ecology of the aquatic fauna associated with the pitcher plant Sarracenia purpurea L.

Larvae of Metriocnemus knabi (Chironomidae) and Wyeomyia smithii (Culicidae) are frozen into their habitat for about 4 months in the winter. Under these conditions the overwintering mortality is estimated to be less than 5%.