Delusions of parasitosis: a survey of entomologists from a psychiatric perspective

A flea activity monitor of potential use to vector ecologists in the testing of insecticides and in the study of flea behavior has been developed. The monitor is designed to detect both` running' and` jumping' activity of fleas in response to a variety of environmental and host-derived cues. With a modular, highly adaptable computer driven monitor, it allows various experiments to be conducted simultaneously. INTRODUCTION A thin membrane of stretched plastic formed the base of the chamber. Each chamber fitted into a socket The automatic recording of flea activity using an within the monitor so that the plastic membrane rested insect monitor was first attempted by Greenwood et al. on a microphone situated at the base of the socket. When 1991) using bird fleas of the genus Ceratophyllus. In the fleas jumped, the resulting vibrations ' on the the present study, the oriental rat flea, Xenopsyllacheopis membrane were detected by the microphone. These Rothschild), the principal vector of Yersinia pestis, has vibrations were transmitted by an operational amplifier been used as a model in a new updated design of the after amplification of the voltage, and shaped into a monitor to test ifchanges can be measured in the activity pulse by a Schmitt trigger circuit. Trials performed with patterns of fleas in response to light. Once a baseline the monitor connected to an oscilloscope showed that profile for each species is determined, the speciesfor every take off and landing only one pulse was specific profiles may be used to measure responses to a recorded. Pulses were counted on a two-bit binary variety of stimuli and allow comparisons to be made coded decimal counter, which was decoded anddisplayed among species, giving a further insight into their behavior on a computer screen according to the numbers ofjumps and ecology. in each chamber. The running activity was detected by two infrared MATERIALS AND METHODS beams, which crossed over at the base of the chamber. These were produced by two infrared emitters In Siphonaptera, running and jumping gaits can be approximately 1 mm in diameter and were detected by detected and used as a measure of activity. The original phototransistors. When running occurred, the infrared monitor reported by Greenwood et al.( 1991) was based beams were broken and a voltage signal from the on only one experimental chamber, a feature that phototransistors was amplified using an operational restricted experimental design and the repetition of amplifier and a pulse produced using a Schmitt trigger trials. In the updated version of the monitor, a module circuit. This was displayed on the computer screen as of four chambers was used. Three of these were the number of runs per chamber. The length of time for experimental chambers( containing fleas) and one was each trial could be programmed and set for any unit from used as a control( no fleas). Any extraneous vibration or 1 minute to 24 hours duration. The number of runs and disturbance that was detected and recorded by the monitor jumps could be recorded at intervals of one, to several could then be accounted for and the profiles adjusted. minutes, to hours. The chambers were initially made ofclear plastic tubing Fleas were removed fromculture using an aspirator but these produced a considerable amount of static attached to a vacuum line. Carbon dioxide was then electricity that often caused the fleas to adhere to the blown into the aspirator to anesthetize the fleas. They walls of the chambers. Therefore, the plastic was were then removed from the aspirator onto a plate made replaced with glass tubing ( 8 cm in length; 2 cm in of porous polyethylene through which CO2 was bled, diameter). keeping the fleas anesthetized as they were manipulated 1Presented at the VII European Annual SOVE Meeting, Bologna, ITALY, 25 August 1992. 2Department of Zoology, University of Leicester, Leicester, ENGLAND 3University of Technology, Loughborough, ENGLAND JUNE, 1993 BULL. SOC. VECTOR ECOL. 27 into the activity chambers. This was done using a pair on log10 transformed data showed no significant of soft-nosed stork' s bill forceps that appeared not to difference between the three treatments ( TABLE 1), damage the fleas. and all trials were therefore conducted on batches of five The flea cultures used in the trials were kept without fleas taken randomly from culture. light and all procedures were carried out under red light 620 nm). This minimized the number of stimuli to Length of Trials which the fleas were exposed prior to any experiment. Trials of different duration were tested from five Red light was chosen because in a previous study of minutes to two hours duration and with various recording spectral efficiency, Crum et al.( 1974) showed that X. intervals, from one to ten minutes. From these an cheopis was least sensitive to the longer wavelengths. experimental time of one hour was chosen, recording All trials were conducted at 25+ 1° C in a darkened jumps and runs every minute. Each experiment began constant temperature room, the temperature at which with a settling period of 15 minutes with no light. There the colony of X. cheopis was maintained. When the was evidence that the performance of the fleas diminished mouse nest box was removed for subculturing every 21 with time, and one hour appeared to be long enough to days, all adult fleas were removed leaving only larvae. detect any effects produced from the stimulus being After a further 1421 days emerging, fleas were used in studied. the trials described below. An approximate age of the fleas could therefore be estimated but it was not known Effects of CO2 if they were mated or unmated. Xenopsylla cheopis were anesthetized with CO2 before they were introduced into the monitor and their RESULTS activity was compared with that of fleas that had not been anesthetized( three replicates of five fleas each). A Density Effects ttest between the two treatments performed on log10Figures la to Id illustrate examples of typical results transformed data showed that there was significantly from trials conducted with 1, 2, 5, and 10 individuals per more activity in the fleas that had not been anesthechamber. When single fleas were used, few jumps were tized than those given CO2 ( mean + SE with CO2= recorded, whereas, at higher densities of 10 fleas, only 1. 0560+0.040; withoutCO2= 1. 449+ 0.023; t= 8.47 DF=2 jumps with few runs were detected. All subsequent P< 0.001). experiments were conducted with five individuals per chamber as the number of runs and jumps were of Variations Within Treatment similar magnitude. This insured that when using different The data for runs and jumps per minute from ten stimuli, only one gait may be affected and detected by trials are shown in Figure 2. Although there is the treatment. considerable variation between replicates within a treatment at each time unit, when the total jumps or runs Differences in the Sexes were taken for each replicate and logtransformed, the Evidence suggests that for some flea species, one error was sufficiently small that these data could be used sex may be more active that the other( Marshall 1981). for comparison with data from other treatments. This Trials using each sex separately and in a random mix as may be seen in the ANOVAs for running and jumping from culture were undertaken. A oneway analysis of between the two sexes run separately and in combination variance( ANOVA) for total activity( runs and jumps) ( TABLE 1). TABLE 1. ANOVA( Log lo) using total activity between five males, five females, and a mixture of five males/ females Xenopsylla cheopis in combination, in nolight treatment at 25° C( 10 replicates each).