Mosquito Community Composition, Seasonal Distributions, and Trap Bias in Northeastern Florida

Mosquito control agencies monitor mosquito diversity and abundance through a variety of trap types. Although various long-term ecological data sets exist, little work has been done to address the sampling effort required to capture mosquito community diversity by trap type and few spatiotemporal distributions of vector species have been described. Here, we describe the seasonal distributions of vector species of importance, assess trapping effort needed to capture the diversity of the mosquito community, and use a partial redundancy analysis to identify trap bias from four commonly deployed adult mosquito traps in Volusia County, Florida. Collections were made with American Biophysics Corporation (ABC) light traps, Biogents Sentinel (BGS) traps, chicken coop exit traps, and gravid traps. We collected a total of 238,301 adult female mosquitoes belonging to 11 genera and 36 species, 12 of which we deemed to be vector species of epidemiological importance. We found that ABC traps not only yielded the greatest abundance and diversity but also captured several nonvector species. BGS and gravid traps yielded the highest proportions of vector species; exit traps recorded the lowest abundances and species richness. Wintertime abundances of several species demonstrated a need for year-round surveillance in the study area; partial redundancy analysis revealed that trap type explained a significant proportion of the variance in our data set, with certain vector species associated with specific trap types. Increased awareness regarding the amount of trapping effort needed to detect vector species diversity will help to optimize efforts in the field, leading to more effective resource allocation.

Multiple captures of fulvous harvest mice (Reithrodontomys fulvescens) and northern pygmy mice (Baiomys taylori): evidence for short-term co-traveling

Multiple captures of small mammals (finding >1 animal in a single trap) are often used to infer pair-bonding activity in arvicoline and cricetine rodents. We analyzed data from a 2-year trapping study to determine whether fulvous harvest mice ( Reithrodontomys fulvescens J.A. Allen, 1894) and (or) northern pygmy mice (Baiomys taylori (Thomas, 1887)) travel in mixed-sex mated pairs. A significant majority of multiple capture events (MCEs) in R. fulvescens were mixed-sex, whereas sex composition of pairs in B. taylori did not differ from random. Multiple capture probability was significantly positively related to abundance and unrelated to sex ratio in both species. Multiple captures of B. taylori were more common in winter, suggesting that individuals may associate to huddle for warmth. Masses of singly captured and multiply captured individuals were not significantly different in either species, contraindicating trap bias. Only one co-captured mixed-sex pair was recaptured as a pair (in R. fulvescens) and several animals of both sexes in both species were co-captured with multiple individuals. We concluded that R. fulvescens co-travels with mates for variable lengths of time, but we found no evidence that multiple captures of B. taylori are related to reproductive behavior.

Eye Colour, Aging, and Decoy Trap Bias in Lesser Scaup, Aythya affinis

Researchers routinely assume that samples of trapped or captured animals are representative of the overall population, though these assumptions are not always evaluated. We used decoy-trapped Lesser Scaup (Aythya affinis) to assess the reliability of classifying females as yearlings or adults from a distance, based on documented age-related eye-colour changes, and also to evaluate the presence of sex, condition and age biases in decoy trapping. We compared eye colour of trapped females to photographs of known-age females following a published procedure while females were (1) in traps (by using spotting scopes or binoculars) and (2) in-hand. Assuming in-hand age assessments were correct, we found that adults aged from a distance were frequently misclassified as yearlings, but yearlings were never misclassified as adults. Distance between observer and female, overall observation quality, and cloud cover did not influence age assignment success. A larger proportion of males was captured than observed during a survey of the local breeding population. We also found that decoy-trapped females had lower body mass and were more likely to be yearlings compared to pass- and jump-shot females from the same area. We conclude that female Lesser Scaup cannot be accurately aged from a distance using eye colour and concur with other researchers that possible sex, age and condition biases should be evaluated when using decoy traps.

Apparent predation of juvenile coho salmon (Oncorhynchus kisutch) by prickly sculpins (Cottus asper) is an artefact of trapping methodology

Freshwater sculpins often inhabit the same waterways as juvenile salmonids and may impact the survival of juvenile salmonids through predation on early life-history stages. In the present study, the stomach contents of 2302 individual Cottus asper, a freshwater sculpin, collected from Auke Lake, Alaska, were examined during the boreal summer of 2000 to determine if C. asper are important natural predators of juvenile coho salmon (Oncorhynchus kisutch), and to explore possible trap bias of gear used in preliminary diet studies. The diet of sculpins collected in confining traps was compared with the diet of sculpins collected in nets. Significant predation on pre-smolt coho salmon by trapped sculpins, but none by netted sculpins, was observed. This result provides strong evidence of trap bias in the observed diet of C. asper. The remainder of the diet of trapped sculpins also differed significantly from that of netted sculpins. Significantly more trapped sculpins had eaten plant material and fish, whereas significantly more netted sculpins had consumed molluscs. Finally, sculpin diet was correlated with sculpin size, which may influence predation on other salmonid life-stages. These results expand our understanding of prickly sculpin diet and show that they are not important predators of juvenile coho salmon. These findings also demonstrate the importance of assessing the potential bias of collection gear and sampling techniques.

A test of the condition-bias hypothesis using Brown-headed Cowbirds trapped during the breeding season

We examined trap bias relative to body condition, age, and sex using data collected from Brown-headed Cowbirds (Molothrus ater) decoy trapped during the 1987 and 1988 breeding seasons. A condition bias was evident, as decoy-trapped birds were in poor condition relative to those caught by mist net in an adjacent roost. This occurred in both sexes and independently of study year and male age. Paradoxically, however, males in better condition when first trapped were more likely to be recaptured in the same season, possibly reflecting more widespread movement, and hence fewer encounters with traps, by birds in poor condition. Hatching-year birds were more likely than adults to be recaptured in the same season. Trapped samples were strongly male biased, which probably reflects a difference in nutritional requirements, and thus foraging strategies, between males and females during the breeding season. This study indicates that biases among birds trapped by methods that rely on a feeding response are likely to be widespread and difficult to predict, suggesting that interpretation of data from such samples always requires caution.

An analysis of multiple captures in Permoyscus with a critique on methodology

Multiple captures obtained in Sherman traps are reported for Peromyscus maniculatus (66 intraspecific, 6 interspecific) and P. difficilis (12 intraspecific, 4 interspecific) in Colorado. Multiple capture frequency in P. maniculatus. (3.53%) was higher than in P. difficilis (1.94%), which probably resulted from the greater weights of P. difficilis. Only one case of injury or death was noted in 84 multiple captures. Multiple captures occurred in traps in which the treadles were significantly less sensitive to tripping than traps that captured single mice, which suggested that pairs of mice did not enter the traps simultaneoulsy. Adult mice were disproportionatley sampled in single captures because of the insensitivity of the tripping mechanism. For the same reason, immature mice were disproportionately sampled in multiple captures. These trap-related biases can create spurious age and sex associations within multiple captures. Trap bias should be tested explicitly before attempting to analyze multiple-capture data from single-capture traps. A "socially null" model of random encounter of traps by captured pairs fits many of the data presented here and is suggested as the appropriate null hypothesis for these analyses. If live-trapping data must be used to address questions of social behavior, the use of actual multiple-capture traps, preferably to study long-term associations between individuals, is suggested.

DIEL PERIODICITY AND TRAP BIAS IN STICKY TRAP SAMPLING OF SHARPNOSED LEAFHOPPER1 POPULATIONS2,3

Sharpnosed leafhoppers, Scaphytopius magdalensis (Provancher), exhibit a diel periodicity characterized by morning and evening peaks of flight activity. Adults are most commonly found on blueberry plants at night; they apparently seek shelter during the day and return to their host plants around dusk. Flight activity during midday and early afternoon is usually correlated with high temperature and low humidity. Most local flight activity occurs from 0 to 50 cm above the soil surface and is significantly affected by bush height.