Movement of AdultCryptolestes ferrugineus(Coleoptera: Laemophloeidae) in Wheat: Response to Temperature Gradients and Gravity

Detecting and Responding to Resource and Stimulus during the Movements of Cryptolestes ferrugineus Adults

“…Therefore, the grain temperature, moisture, and pesticide in most cases might be major factors even though some other factors could be major factors under some situations (Table 1). This assumption was proven by the following experimental results: (1) RGB densities and percentages of dockage do not influence their preference to warmer temperatures (Jian et al 2004a(Jian et al , b, 2005a; (2) wandering movement of RGB adults is restricted by temperature gradients (Jian et al 2004a, b); (3) RGB adults are more sensitive to the moisture differences inside dry grain (Loschiavo 1983) and move faster in 12.5% mc wheat than in 14.5% mc wheat; (4) in damp grain, grain moisture content is a minor factor influencing their movement (Jian et al 2005a, b); (5) RGB adults respond to both temperature gradients and moisture differences in columns of wheat with temperature gradients and moisture content differences (Jian et al 2005a, b); (6) RGB adults stay in warmer locations in both high-and lowmoisture grains (Jian et al 2005a, b); and (7) at different moisture contents, RGB adults change their preference, e.g., prefer the high-moisture grain in dry grain regardless of the direction of temperature gradients and prefer the higher temperature in damp grain regardless of the direction of moisture gradients (Jian et al 2005a, b).…”

“…This movement pattern is demonstrated by several researchers and is named as geotropism or geotaxis (Surtees 1963;Loschiavo 1974Loschiavo , 1983White and Loschiavo 1986;Jian et al 2002Jian et al , 2004a; however, RGB adults do not consistently show this positive "geotactic" behavior inside stored grain bins and at laboratory-controlled conditions (Surtees 1963(Surtees , 1964aSmith and Loschiavo 1978;Smith 1978;Hagstrum 1989;Arbogast and Throne 1997). Therefore, Jian et al (2006) suggested that the downward movement of RGB is partially caused by a drift effect due to beetles sliding between seeds, and the displacement of the adults might be the combined effect of walking and falling during their movements (Jian et al 2006).…”

“…Increasing the time of the hot or cold acclimation causes high aggregation (Jian et al 2005b). Both male and female adults can move into and remain in warm areas of the grain mass (Flinn and Hagstrum 1998;Jian et al 2002Jian et al , 2003Jian et al , 2004a. At temperature gradients of 2.5, 5, or 10°C/m, adults can detect temperature gradients in <1 h and respond faster to higher temperature gradients than to lower temperature gradients (Jian et al 2004a, b).…”

“…These semiochemicals can be produced by the insect themselves, microorganisms, and other arthropod species, including predators and parasitoids. Therefore, even though the insect density of RGB does not influence their distribution, increasing insect densities of RGB increases their diffusivity (Jian et al 2004a(Jian et al , b, 2007. A low percentage of dockage (5% by mass) did not influence RGB adults' movement and distribution (Jian et al 2005a, b); however, fine material and dockage might produce semiochemical compounds.…”

“…Even though dense populations release semiochemicals onto the grain, causing RGB beetles to migrate from the crowded area (Faustini and Burkholder 1987), disturbance between individuals is a relatively minor factor in the dispersion behavior, because the individual is small and light (about 0.3 mg). This might explain why the following are minor factors: gas concentrations (except modified atmosphere), chemical compounds (except pesticides), bulk densities, foreign Burkholder and Ma 1985;Loschiavo et al 1983 Pesticide application Major If insects have no response to the applied pesticide Bell 1986;Donahaye et al 1991;Cox et al 1993;Fields and Korunic 2000;Hou and Fields 2003 Drifting Minor When in uniform temperature and moisture grain without pesticide application Surtees 1963;Loschiavo 1974;White and Loschiavo 1986;Jian et al 2002, 2004a Chang and Loschiavo 1971;Throne 1990, 1993 Minor When at high air flow rate such as insects cannot control their moving Jian (unpublished data) a The environmental factor will be a major or minor factor with the exception at the condition presented in the "exclusive condition" column. The factor will change to its opposite at the exclusive condition materials, insect densities, and insect species (except predators) present in the stored grain mass.…”