Estimated absorbance spectra of the visual pigments of the North Atlantic right whale (Eubalaena glacialis)

To assess the spectral sensitivities of the retinal visual pigments from the North Atlantic right whale (Eubalaena glacialis), we have cloned and sequenced two exons from the rod opsin gene and two exons from the middle‐wavelength sensitive (MWS) cone opsin gene in order to determine the amino acids at positions known to be key regulators of the spectral location of the absorbance maximum (λ_max). Based on previous mutagenesis models we estimate that the right whale possesses a rod visual pigment with a λ_max of 499 nm and a MWS cone visual pigment with a λ_max of 524 nm. Although the MWS cone visual pigment from the right whale is blue‐shifted in its spectral sensitivity like those from odontocetes, the spectral sensitivity of the right whale rod visual pigment is similar to those from terrestrial mammals.     

Spectral sensitivity of the compound eyes in two day-active fireflies (Coleoptera: Lampyridae: Lucidota)

Summary The electroretinographic visual spectral sensitivity functions in day-active fireflies Lucidota luteicollis and Lucidota atra show a broad green sensitivity and a shoulder in the near-ultraviolet region of the spectrum (Figs. 1, 2) as is commonly found among day-active insects. The nomogram for P530 visual pigment matches the spectral sensitivity curves in the green. The adult L. luteicollis retains its larval bioluminescent light organ which has a peak emission at 562 nm. The _max of the ERG spectral sensitivity does not match the bioluminescent peak (Fig. 1B) as it does in twilight- and dark-active fireflies. Some relevant behavioural observations with respect to mating are presented.     

Spectral absorption and sensitivity measurements in single ommatidia of the green crab,Carcinus

Summary Rhabdoms of the green crabCarcinus maenas were examined by microspectrophotometry and found to contain a visual pigment with _max at 502–506 nm. Upon irradiation, a stable metarhodopsin formed with unchanged _max and molar extinction coefficient. In the presence of 5% glutaraldehyde the rhabdoms were photobleached. Partial bleaching experiments indicate that in the rhabdoms studied, only one visual pigment was present, with an absorption spectrum appropriate for a hypothetical rhodopsin from Dartnall's (1953) nomogram.Retinular (photoreceptor) cells were studied with microelectrodes. They had negative resting potentials of 30–65 mV and responded to light with depolarizing receptor potentials. All cells had maximum sensitivity at ~493 nm, as did the ERG (electroretinogram). Selective adaptation failed to alter the spectral sensitivity functions of single cells or the ERG. If these spectral sensitivity data are pooled with Wald's (1968), the average sensitivity of the dark-adapted eye is accounted for adequately by the pigment of the rhabdom.The results of this work do not support the hypothesis of Horridge (1967) that each ommatidium ofCarcinus has two color receptors.This work was supported by U.S. P.H.S. grant EY 00222.     

Electroretinogram and the spectral sensitivity of the compound eyes in the firefly Photuris versicolor (Coleoptera-Lampyridae): A correspondence between green sensitivity and species bioluminescence emission

ERGs were recorded from the dorsal sector of dark- and chromatic-adapted compound eyes in the dark-active firefly Photuris versicolor ♀ and ♂ at different wavelengths across the spectrum ranging from 320 nm to 700 nm over 4.5 log units of change in the stimulus intensity. ERG elicited by white light stimulus was an on-negative monophasic wave typical of scotopic eyes. ERGs elicited by chromatic stimuli differed in their waveform characteristics in the short (near-u.v. and violet) and long (green-yellow) wavelengths. The slope of the intensity-response curves at different stimulus wavelengths were similar for phasic response and differed for the plateau component of the ERG. The spectral sensitivity curves obtained under dark- and chromatic-adapted conditions revealed peaks in the near-u.v. (λ_max, 380 nm) and in the green (λ_max 550 nm), suggesting the presence of at least two receptor types in the dorsal sector of the compound eyes of P. versicolor. The green (550 nm) peak corresponds with the species bioluminescence emission peak (552 nm).     

Wavelength-dependent induction of UV-absorbing mycosporine-like amino acids in the red alga Chondrus crispus under natural solar radiation

Polychromatic response spectra for the induction of UV absorbing mycosporine-like amino acids (MAAs) were calculated after exposing small thalli of the red alga Chondrus crispus under various cut-off filters to natural solar radiation on the North Sea island Helgoland, Germany. The laboratory-grown specimens typically contain only traces of palythine and synthesise five different MAAs rapidly and in high concentrations after being transplanted into shallow water. The resulting qualitative and quantitative patterns of MAA induction differed markedly with respect to spectral distribution. Furthermore, the wavebands effective for MAA induction vary within the MAA. UV-B radiation had a negative effect on the accumulation of the major MAAs shinorine (λ_max=334 nm) and palythine (λ_max=320 nm), while short wavelength UV-A exhibits the highest quantum efficiency on their synthesis. In contrast, the synthesis of asterina-330 (λ_max=330 nm), palythinol (λ_max=332 nm) and palythene (λ_max=360 nm) was mainly induced by UV-B radiation. Whether the synthesis of shinorine and palythine is induced by a photoreceptor with an absorption maximum in the short wavelength UV-A and whether a second photoreceptor absorbing UV-B radiation is responsible for the induction of asterina-330, palythinol and palythene remains to be studied.Our results show that C. crispus has a high capacity to adapt flexibly the qualitative and quantitative MAA concentration to the prevailing spectral distribution of irradiance. On one hand, this is regarded as an important aspect with respect to the acclimation of algae to increasing UV-B irradiance in the context of ongoing depletion of stratospheric ozone. On the other hand, the experiment demonstrates that UV-A irradiance is more important for the induction of the major MAAs shinorine and palythine than UV-B.     

Compound eyes and ocular pigments of crustacean larvae (Stomatopoda and decapoda,brachyura)

Larvae of decapod and stomatopod crustaceans possess paired compound eyes not unlike those of adult crustaceans. However, the visual demands of larval and adult life differ considerably. Furthermore, the eyes of adult stomatopods appear to be far more specialized than those of the larvae. We examined eyes of several stomatopod species just before and after larval metamorphosis. At this time, the entire larval retina is joined by a new, adult‐type retinal array which gradually replaces the remnants of the larval retina. The new retina of the postlarva is anatomically similar to that of the full‐grown adult, and has virtually identical assemblages of intrarhabdomal filters. We determined the photopigments of Gonodactylus aloha, the only species for which we were able to obtain both larval and adult specimens, using microspectrophotometry. The single middle‐wavelength larval rhodopsin (λ_max= 499 nm) disappears at metamorphosis; none of the 10 classes of adult rhodopsins has λ_max between 473 and 510 nm. This metamorphic change of visual pigment does not occur in a comparison species of decapod crustacean, the blue crab Callinectes sapidus. Here, rhodopsins both of the megalops larva and the adult had λ_max at 503–504 nm. The difference between these two species can be explained by the varying ecological requirements of their larvae and adults, and more study of visual pigments in retinas of larval and adult crustaceans is warranted.     

Spectral Sensitivity of Larval Mosquito Ocelli

The spectral sensitivity of lateral ocelli in both wild-type and white-eyed larvae of the yellow fever mosquito Aedes aegypti L. (reared in darkness) was measured by means of the electroretinogram. The spectral sensitivity is maximal at about 520 nm, with a small secondary peak near 370 nm. When allowance is made for some screening and filtering by the eye tissues, the spectral sensitivity is in reasonable agreement with the absorption spectrum of ocellar rhodopsin (λ_max = 515 nm).     

Variation in rod spectral sensitivity of fishes is best predicted by habitat and depth

Rod spectral sensitivity data (λ_max), measured by microspectrophotometry, were compiled for 403 species of ray-finned fishes in order to examine four hypothesized predictors of rod spectral sensitivity (depth, habitat, diet and temperature). From this database, a subset of species that were known to be adults and available on a published phylogeny (n = 210) were included in analysis, indicating rod λ_max values averaging 503 nm and ranging from 477 to 541 nm. Linear models that corrected for phylogenetic relatedness showed that variation in rod sensitivity was best predicted by habitat and depth, with shorter wavelength λ_max values occurring in fishes found offshore or in the deep sea. Neither diet, nor the interaction of diet and habitat, had significant explanatory power. Although temperature significantly correlated with rod sensitivity, in that fishes in temperate latitudes had longer wavelength rod λ_max values than those in tropical latitudes, sampling inequity and other confounds require the role of the temperature to be studied further. Together, these findings indicate that fish rod λ_max is influenced by several ecological factors, suggesting that selection can act on even small differences in fish spectral sensitivity.     

Action Spectra and Adaptation Properties of Carp Photoreceptors

The mass photoreceptor response of the isolated carp retina was studied after immersing the tissue in aspartate-Ringer solution. Two electro-retinogram components were isolated by differential depth recording: a fast cornea-negative wave, arising in the receptor layer, and a slow, cornea-negative wave arising at some level proximal to the photoreceptors. Only the fast component was investigated further. In complete dark adaptation, its action spectrum peaked near 540 nm and indicated input from both porphyropsin-containing rods (λ_max ≈ 525 nm) and cones with longer wavelength sensitivity. Under photopic conditions a broad action spectrum, λ_max ≈ 580 nm was seen. In the presence of chromatic backgrounds, the photopic curve could be fractionated into three components whose action spectra agreed reasonably well with the spectral characteristics of blue, green, and red cone pigments of the goldfish. In parallel studies, the carp rod pigment was studied in situ by transmission densitometry. The reduction in optical density after a full bleach averaged 0.28 at its λ_max 525 nm. In the isolated retina no regeneration of rod pigment occurred within 2 h after bleaching. The bleaching power of background fields used in adaptation experiments was determined directly. Both rods and cones generated increment threshold functions with slopes of +1 on log-log coordinates over a 3–4 log range of background intensities. Background fields which bleached less than 0.5% rod pigment nevertheless diminished photoreceptor sensitivity. The degree and rate of recovery of receptor sensitivity after exposure to a background field was a function of the total flux (I x t) of the field. Rod saturation, i.e. the abolition of rod voltages, occurred after ≈12% of rod pigment was bleached. In light-adapted retinas bathed in normal Ringer solution, a small test flash elicited a larger response in the presence of an annular background field than when it fell upon a dark retina. The enhancement was not observed in aspartate-treated retinas.     

Questing activity in bed bug populations: male and female responses to host signals

A large‐arena bioassay is used to examine sex differences in spatiotemporal patterns of bed bug Cimex lectularius L. behavioural responses to either a human host or CO₂ gas. After release in the centre of the arena, 90% of newly‐fed bed bugs move to hiding places in the corners within 24 h. They require 3 days to settle down completely in the arena, with generally low activity levels and the absence of responses to human stimuli for 5 days. After 8–9 days, persistent responses can be recorded. Sex differences are observed, in which females are more active during establishment, respond faster after feeding, expose themselves more than males during the daytime, and respond more strongly to the host signal. The number of bed bugs that rest in harbourages is found to vary significantly according to light setting and sex. Both sexes stay inside harbourages more in daylight compared with night, and males hide more than females during the daytime but not during the night. The spatial distribution of the bed bugs is also found to change with the presence of CO₂, and peak aggregation around the odour source is observed after 24 min. Both male and female bed bugs move from hiding places or the border of the arena toward the centre where CO₂ is released. Peak responses are always highest during the night. Bed bug behaviour and behaviour‐regulating features are discussed in the context of control methods.     

Potential population growth and harmful effects on humans from bed bug populations exposed to different feeding regimes

Effects of host availability and feeding period on bed bugs, Cimex lectularius (L.) (Hemiptera: Cimicidae), were measured. Population growth and the potential harmful effect of bed bug populations on human hosts were modelled. Bloodmeal sizes were affected by both feeding length and frequency, with >2‐fold difference between insects fed daily or weekly. Blood consumption increased >2‐fold between bed bugs fed occasionally and often, and 1.5‐fold between occasional and daily feeding. Bed bugs fed more often than once a week, potentially every 2–4 days. Egg production was associated with nutrition, being strongly correlated with blood consumption in the previous week. Bed bug populations can grow under different feeding regimes and are hard to control with <80% mortality. Bed bugs can survive and grow even in locations with a limited blood supply, where bed bug persistence may be important for the continual spread of populations. Persistence in non‐traditional locations and a potential association with human pathogens increase the health risks of bed bugs. Potential blood loss as a result of a bed bug can have serious consequences because uncontrolled populations can reach harmful levels in 3–8 months. The reproduction potential of bed bug populations suggests serious consequences to human health and the need for efficacious control measures.     

A look into the invisible: ultraviolet-B sensitivity in an insect (Caliothrips phaseoli) revealed through a behavioural action spectrum

Caliothrips phaseoli, a phytophagous insect, detects and responds to solar ultraviolet-B radiation (UV-B; λ ≤ 315 nm) under field conditions. A highly specific mechanism must be present in the thrips visual system in order to detect this narrow band of solar radiation, which is at least 30 times less abundant than the UV-A (315–400 nm), to which many insects are sensitive. We constructed an action spectrum of thrips responses to light by studying their behavioural reactions to monochromatic irradiation under confinement conditions. Thrips were maximally sensitive to wavelengths between 290 and 330 nm; human-visible wavelengths (λ ≥ 400 nm) failed to elicit any response. All but six ommatidia of the thrips compound eye were highly fluorescent when exposed to UV-A of wavelengths longer than 330 nm. We hypothesized that the fluorescent compound acts as an internal filter, preventing radiation with λ > 330 nm from reaching the photoreceptor cells. Calculations based on the putative filter transmittance and a visual pigment template of λ_max = 360 nm produced a sensitivity spectrum that was strikingly similar to the action spectrum of UV-induced behavioural response. These results suggest that specific UV-B vision in thrips is achieved by a standard UV-A photoreceptor and a sharp cut-off internal filter that blocks longer UV wavelengths in the majority of the ommatidia.     

Photoreceptor Spectral Sensitivity in the Bumblebee,Bombus impatiens (Hymenoptera: Apidae)

The bumblebee Bombus impatiens is increasingly used as a model in comparative studies of colour vision, or in behavioural studies relying on perceptual discrimination of colour. However, full spectral sensitivity data on the photoreceptor inputs underlying colour vision are not available for B. impatiens. Since most known bee species are trichromatic, with photoreceptor spectral sensitivity peaks in the UV, blue and green regions of the spectrum, data from a related species, where spectral sensitivity measurements have been made, are often applied to B impatiens. Nevertheless, species differences in spectral tuning of equivalent photoreceptor classes may result in peaks that differ by several nm, which may have small but significant effects on colour discrimination ability. We therefore used intracellular recording to measure photoreceptor spectral sensitivity in B. impatiens. Spectral peaks were estimated at 347, 424 and 539 nm for UV, blue and green receptors, respectively, suggesting that this species is a UV-blue-green trichromat. Photoreceptor spectral sensitivity peaks are similar to previous measurements from Bombus terrestris, although there is a significant difference in the peak sensitivity of the blue receptor, which is shifted in the short wave direction by 12–13 nm in B. impatiens compared to B. terrestris.     

Trichromatic visual system in an insect and its sensitivity control by blue light

Summary The spectral sensitivity of the visual cells in the compound eye of the mothDeilephila elpenor was determined by electrophysiological mass recordings during exposure to monochromatic adapting light. Three types of receptors were identified. The receptors are maximally sensitive at about 350 nm (ultraviolet), 450 nm (violet), and 525 nm (green). The spectral sensitivity of the green receptors is identical to a nomogram for a rhodopsin with _max at 525 nm. The spectral sensitivity of the other two receptors rather well agrees with nomograms for corresponding rhodopsins. The recordings indicate that the green receptors occur in larger number than the other receptors. The ultra-violet and violet receptors probably occur in about equal number.The sensitivity after monochromatic adapting illumination varies with the wavelength of the adapting light, but is not proportional to the spectral sensitivity of the receptors. The sensitivity is proportional to the concentration of visual pigment at photoequilibrium. The equilibrium is determined by the absorbance coefficients of the visual pigment and its photoproduct at each wavelength. The concentration of the visual pigment, and thereby the sensitivity, is maximal at about 450 nm, and minimal at wavelengths exceeding about 570 nm.The light from a clear sky keeps the relative concentration of visual pigment in the green receptors, and the relative sensitivity, at about 0.62. The pigment concentration in the ultra-violet receptors is about 0.8 to 0.9, and that in the violet receptors probably about 0.6. At low ambient light intensities a chemical regeneration of the visual pigments may cause an increase in sensitivity. At higher intensities the concentrations of the visual pigments remain constant. Due to the constant pigment concentrations the input signals from the receptors to the central nervous system contain unequivocal information about variations in intensity and spectral distribution of the stimulating light.The work reported in this article was supported by the Swedish Medical Research Council (grant no B 73-04X-104-02B), by Karolinska Institutet, and by a grant (to G. Höglund) from Deutscher Akademischer Austauschdienst, and by the Deutsche Forschungsgemeinschaft, Schwerpunktsprogramm Rezeptorphysiologie HA 258-10, and SFB 114.     

Effectiveness of bed bug monitors for detecting and trapping bed bugs in apartments

Bed bugs, Cimex lectularius L., are now considered a serious urban pest in the United States. Because they are small and difficult to find, there has been strong interest in developing and using monitoring tools to detect bed bugs and evaluate the results of bed bug control efforts. Several bed bug monitoring devices were developed recently, but their effectiveness is unknown. We comparatively evaluated three active monitors that contain attractants: CDC3000, NightWatch, and a home-made dry ice trap. The Climbup Insect Interceptor, a passive monitor (without attractants), was used for estimating the bed bug numbers before and after placing active monitors. The results of the Interceptors also were compared with the results of the active monitors. In occupied apartments, the relative effectiveness of the active monitors was: dry ice trap > CDC3000 > NightWatch. In lightly infested apartments, the Interceptor (operated for 7 d) trapped similar number of bed bugs as the dry ice trap (operated for 1 d) and trapped more bed bugs than CDC3000 and NightWatch (operated for 1 d). The Interceptor was also more effective than visual inspections in detecting the presence of small numbers of bed bugs. CDC3000 and the dry ice trap operated for 1 d were equally as effective as the visual inspections for detecting very low level of infestations, whereas 1-d deployment of NightWatch detected significantly lower number of infestations compared with visual inspections. NightWatch was designed to be able to operate for several consecutive nights. When operated for four nights, NightWatch trapped similar number of bed bugs as the Interceptors operated for 10 d after deployment of NightWatch. We conclude these monitors are effective tools in detecting early bed bug infestations and evaluating the results of bed bug control programs.     

Why Aye‐Ayes See Blue

The capacity for cone‐mediated color vision varies among nocturnal primates. Some species are colorblind, having lost the functionality of their short‐wavelength‐sensitive‐1 (SWS1) opsin pigment gene. In other species, such as the aye‐aye (Daubentonia madagascariensis), the SWS1 gene remains intact. Recent studies focused on aye‐ayes indicate that this gene has been maintained by natural selection and that the pigment has a peak sensitivity (λ_max) of 406 nm, which is ～20 nm closer to the ultraviolet region of the spectrum than in most primates. The functional significance behind the retention and unusual λ_max of this opsin pigment is unknown, and it is perplexing given that all mammals are presumed to be colorblind in the dark. Here we comment on this puzzle and discuss recent findings on the color vision intensity thresholds of terrestrial vertebrates with comparable optics to aye‐ayes. We draw attention to the twilight activities of aye‐ayes and report that twilight is enriched in short‐wavelength (bluish) light. We also show that the intensity of twilight and full moonlight is probably sufficient to support cone‐mediated color vision. We speculate that the intact SWS1 opsin pigment gene of aye‐ayes is a crepuscular adaptation and we report on the blueness of potential visual targets, such as scent marks and the brilliant blue arils of Ravenala madagascariensis.     

Structure and siderophore activity of ferric schizokinen

Schizokinen, a citrate-containing dihydroxamate, is a siderophore produced by Bacillus megaterium and Anabaena sp. The involvement of the citrate α-hydroxycarboxylate moiety in iron chelation was investigated by comparing the iron binding behavior of schizokinen with that of acetylschizokinen, a derivative in which the citrate hydroxyl group was modified by acetylation. Ferric schizokinen was found to exhibit an absorption spectrum (λ_max = 460 nm) characteristic of a dihydroxamate below pH 2.5, with an isosbestic shift to a citrate dihydroxamate spectrum (λ_max = 395 nm) above pH 4. Ferric acetylschizokinen also had a dihydroxamate absorption spectrum (λ_max = 465 nm) at low pH. However, its spectral shift (λ_max = 420 nm) and intensity above pH 4 were more typical of a ferric trihydroxamate. The molecular weight and electrophoretic mobility of ferric acetylschizokinen are consistent with a dimeric Fe₂ (acetylschizokinen)₃ structure, whereas ferric schizokinen appears to exist as a monomeric 1:1 complex Despite the differences in molecular weight and α-hydroxycarboxylate coordination, both complexes are effective in promoting iron uptake in Anabaena.     

Comparative visual ecology of cephalopods from different habitats

Previous investigations of vision and visual pigment evolution in aquatic predators have focused on fish and crustaceans, generally ignoring the cephalopods. Since the first cephalopod opsin was sequenced in late 1980s, we now have data on over 50 cephalopod opsins, prompting this functional and phylogenetic examination. Much of this data does not specifically examine the visual pigment spectral absorbance position (λ_max) relative to environment or lifestyle, and cephalopod opsin functional adaptation and visual ecology remain largely unknown. Here we introduce a new protocol for photoreceptor microspectrophotometry (MSP) that overcomes the difficulty of bleaching the bistable visual pigment and that reveals eight coastal coleoid cephalopods to be monochromatic with λ_max varying from 484 to 505 nm. A combination of current MSP results, the λ_max values previously characterized using cephalopod retinal extracts (467–500 nm) and the corresponding opsin phylogenetic tree were used for systematic comparisons with an end goal of examining the adaptations of coleoid visual pigments to different light environments. Spectral tuning shifts are described in response to different modes of life and light conditions. A new spectral tuning model suggests that nine amino acid substitution sites may determine the direction and the magnitude of spectral shifts.     

Role of Vision and Mechanoreception in Bed Bug,Cimex lectularius L. Behavior

The role of olfactory cues such as carbon dioxide, pheromones, and kairomones in bed bug, Cimex lectularius L. behavior has been demonstrated. However, the role of vision and mechanoreception in bed bug behavior is poorly understood. We investigated bed bug vision by determining their responses to different colors, vertical objects, and their ability to detect colors and vertical objects under low and complete dark conditions. Results show black and red paper harborages are preferred compared to yellow, green, blue, and white harborages. A bed bug trapping device with a black or red exterior surface was significantly more attractive to bed bugs than that with a white exterior surface. Bed bugs exhibited strong orientation behavior toward vertical objects. The height (15 vs. 30 cm tall) and color (brown vs. black) of the vertical object had no significant effect on orientation behavior of bed bugs. Bed bugs could differentiate color and detect vertical objects at very low background light conditions, but not in complete darkness. Bed bug preference to different substrate textures (mechanoreception) was also explored. Bed bugs preferred dyed tape compared to painted tape, textured painted plastic, and felt. These results revealed that substrate color, presence of vertical objects, and substrate texture affect host-seeking and harborage-searching behavior of bed bugs. Bed bugs may use a combination of vision, mechanoreception, and chemoreception to locate hosts and seek harborages.     

Mark-Release-Recapture Reveals Extensive Movement of Bed Bugs (Cimex lectularius L.) within and between Apartments

Understanding movement and dispersal of the common bed bug (Cimex lectularius L.) under field conditions is important in the control of infestations and for managing the spread of bed bugs to new locations. We investigated bed bug movement within and between apartments using mark-release-recapture (m-r-r) technique combined with apartment-wide monitoring using pitfall-style interceptors. Bed bugs were collected, marked, and released in six apartments. The distribution of marked and unmarked bed bugs in these apartments and their 24 neighboring units were monitored over 32 days. Extensive movement of marked bed bugs within and between apartments occurred regardless of the number of bed bugs released or presence/absence of a host. Comparison of marked and unmarked bed bug distributions confirms that the extensive bed bug activity observed was not an artifact of the m-r-r technique used. Marked bed bugs were recovered in apartments neighboring five of six m-r-r apartments. Their dispersal rates at 14 or 15 d were 0.0–5.0%. The estimated number of bed bugs per apartment in the six m-r-r apartments was 2,433–14,291 at 4–7 d after release. Longevity of bed bugs in the absence of a host was recorded in a vacant apartment. Marked large nymphs (3^rd– 5^th instar), adult females, and adult males continued to be recovered up to 57, 113, and 134 d after host absence, respectively. Among the naturally existing unmarked bed bugs, unfed small nymphs (1^st– 2^nd instar) were recovered up to 134 d; large nymphs and adults were still found at 155 d when the study ended. Our findings provide important insight into the behavioral ecology of bed bugs in infested apartments and have significant implications in regards to eradication programs and managing the spread of bed bugs within multi-occupancy dwellings.