The Responses of the Bed Bug (Cimex Lectularius L.) to Heat Exposure at the Population, Behavioral, and Physiological Levels
Abstract
Elimination of bed bug infestations remains a challenge for the pest management industry as these insects continue to resurge on a global scale. However, the use of integrated pest management (IPM) to control bed bugs has been effective. A key part of an IPM program is the combined use of chemical and non-chemical techniques, and one effective non-chemical technique is the use of lethal heat. When properly done, heat treatments can eliminate all bed bug life stages. However, household items with variable thermal conductivities can lead to uneven temperatures within the structures being treated. Uneven heating of bed bug harborage areas may allow bed bugs to behaviorally respond to heat exposure by escaping to cooler zones or be exposed to sub-lethal heat when within hiding places. Survival of bed bugs immediately following heat treatments could mainly occur due to two reasons: (1) the ability of bed bugs to develop physiological heat resistance; and (2) their ability to chemically (through release of alarm pheromones) and behaviorally respond to lethal heat exposure by escaping to cooler spots or areas that have been sub-lethally heated, which has not been investigated. Therefore, the main objectives of this study are: 1) Evaluate ability of bed bugs to develop heat resistance or thermo-tolerance at the population level in relation to their history of previous heat exposure, insecticide resistance status, and geographic origin using two different exposure techniques. 2) Determine the temperatures that will stimulate bed bugs to move in search for cooler areas. 3) Identify which HSP genes are expressed by bed bugs after heat exposure. 4) Determine if alarm pheromones (APs) are released by bed bugs that are heat exposed and how conspecifics that are not exposed to heat will react to these APs. For the first objective, selection experiments found an initial increase in bed bug survivorship over the first 2–3 generations; however, survivorship did not increase past the fourth generation. The step-function exposure technique revealed non-significant variation in heat tolerance between populations and the ramp-function exposure technique provided similar results. Based on this objective 1 findings, the ability of bed bugs to develop heat resistance within a few generations appears to be limited. Behavioral experiments (objective 2) found that at specific temperatures, different bed bug populations had similar probabilities to flee and their ability to locate unheated areas or survive heat exposure in the arena was not different. Also, if bed bugs are exposed to temperatures of 47–48°C in their harborage while exterior temperatures approach 53–54°C, they will be forced into the open. The RT-qPCR experiments (objective 3) revealed that the expression of the HSP70.1, HSP70.3, and Putative SmallHSP genes were significantly upregulated after heat exposure in all tested populations and are likely critical in their recovery process after heat exposure. For the fourth objective, analysis of head space volatiles, using a SIFT-MS (soft ion flow tube mass spectrometer), revealed that bed bugs responded to lethal and sub-lethal heat exposure by emitting their APs. In separate behavioral experiments, it was shown that conspecifics from both tested populations reacted to APs emitted by heated bed bugs and synthetic APs by frantically moving.
Degree
Ph.D.
Subject Area
Thermodynamics
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