Humans are affected by arthropods in a variety of ways. These effects can be direct, e.g. damage due to stings or bites, or indirect, e.g. transmission of diseases or allergic reactions to bits and stings. Providing a better understanding of the population dynamics and dispersal of medically important arthropods is crucial to our ability to mitigate their negative effects on humans.
For example, bed bug problems have been increasing since the 1980’s, and accordingly, there have been intensive efforts to better understand their biology and behavior for control purposes. Millions of dollars are spent each year for bed bug control. Understanding bed bug diffusion rates and dispersal patterns from one site to another (or lack thereof) is a key component in prevention and control campaigns.
In collaboration with Jerome Goddard (Department of Bio Chemistry, Molecular Biology, Entomology, and Plant Pathology, Mississippi State University) we have explored the dispersal abilities of bed bugs and the spatial distribution and questing abilities of ticks.
Covering all major arthropods of medical importance worldwide, this award-winning resource has established itself as a standard reference for almost 25 years. With the globilization of commerce and the world becoming more intimately connected through the everyday ease of travel, unknown arthropod species are being increasingly encountered. This means access to up-to-date, authoritative information in medical entomology has never been more important. Now in its seventh edition, this book maintains its well-acclaimed status as the ultimate easy-to-use guide to identify disease-carrying arthropods, the common signs and symptoms of vector-borne diseases, and the current recommended procedures for treatment.
Bed bug problems have been increasing since the 1980s, and accordingly, there have been intensive efforts to better understand their biology and behavior for control purposes. Understanding bed bug diffusion rates and dispersal patterns from one site to another (or lack thereof) is a key component in prevention and control campaigns. This study analyzed diffusion rates and dispersal patterns in a population of bed bugs, recently fed and unfed, in both one-dimensional and two-dimensional settings. When placed in the middle of a 71 cm × 2.7 cm artificial lane, approximately half of the bugs regardless of feeding status stayed at or near the release point during the 10 min observation periods, while about a fourth of them walked to the end of the lane. When placed in the middle of an arena measuring 51 cm × 76 cm and allowed to walk in any direction, approximately one-fourth of bed bugs, fed or unfed, still remained near their release point (no significant difference between fed or unfed). As for long-distance dispersal, 11/50 (22%) of recently fed bed bugs moved as far as possible in the arena during the 10 min replications, while only 2/50 (4%) unfed bed bugs moved to the maximum distance. This difference was significantly different (p < 0.0038), and indicates that unfed bed bugs did not move as far as recently fed ones. A mathematical diffusion model was used to quantify bed bug movements and an estimated diffusion rate range of 0.00006 cm2/s to 0.416 cm2/s was determined, which is almost no movement to a predicted root mean squared distance of approximately 19 cm per 10 min. The results of this study suggest that bed bugs, upon initial introduction into a new area, would have a difficult time traversing long distances when left alone to randomly disperse.
Whether or not people get tick-borne diseases (TBD) is related to tick population numbers (the vector), tick infection rates (the pathogen), and exposure of humans and other animals (the hosts). Understanding each of these components and their interplay is important in choosing personal protection measures against ticks as well as prevention/management of TBD. A way of estimating how many ticks occur in a given area would be of great interest to public health officials, as well as how many might actually get on a person during outdoor activities. Tick populations might be sampled and counted directly in small areas, or estimated in larger expanses by using mark-release-recapture (MRR) methods (Daniels et al. 2000, Goddard and Goddard 2008). Collection methods for these MRR studies have included dragging a white cloth around in the woods (drag cloth sampling) and/or walk-around surveys. By using these data, researchers have attempted to design ecological or entomologic risk maps or charts for Lyme disease and other TBD (Davis et al. 1984, Schulze et al. 1991, Daniels et al. 1998, Supergan and Karbowiak 2009). This pilot study attempts to link drag-cloth sampling results to the actual risk of acquiring black-legged ticks, Ixodes scapularis in central Mississippi.
To assess the proportion of lone star ticks questing in an area, a predetermined number of ticks were released into each of 9 wooded/grassy plots in central Mississippi that were known to be free of lone star ticks. Plots were 3 x 15 m and contained 0 (control), 12, 25, and 50 ticks, with two replicates of each. The ninth plot was 2x the size of the others and contained 25 ticks. Plots were then sampled at 3:00 p.m. each day with a 1m2 drag cloth at 24, 48, and 72 hour intervals after tick release. Out of the 199 ticks released, 29 (14.5%) were recaptured at 24 hours, 46 (23.1%) were recaptured at 48 hours, and 36 (18.0%) were recaptured at 72 hours. Size of the plot made little difference in number of ticks collected; the one double-sized plot containing 25 ticks produced sampling results similar to the other, standardsized plots containing the same number of ticks. There were no significant differences in percent tick questing (PTQ) between sites (plots) or times. There was also little relationship between temperature and humidity and PTQ in this study. A logistic regression on the data set showed no significant relationship between tick populations and fraction of ticks questing.
A sequential Bayesian algorithm and accompanying computer program were developed and validated to estimate population numbers of adult blacklegged tick, Ixodes scapularis Say, using mark-release-recapture methodology in field plots in central Mississippi. In fieldwork, data taken in February 2005 in a 1-ha plot yielded an estimate of 317 adult I. scapularis per ha Data from another field plot in 2006, 3 km away, yielded an estimate of 280 adult I. scapularis per ha The number of ticks collected per hour in both plots averaged 4.5. In eight of 14 (57%) of sampling events, the number of ticks collected per hour hovered closely around 5.0 (4.8-5.3). The computer program developed in this study readily produced statistical measures such as mean number of ticks per plot, mode, variance, and standard deviation, as well as easy-to-read graphs of estimated tick populations for each sampling period.
