PHYSIOLOGICAL ECOLOGY Preimaginal Development Response to Constant Temperatures in Hypera postica (Coleoptera: Curculionidae): Picking the Best Model BABAK ZAHIRI, 1 YAGHOUB FATHIPOUR, 1,2 MOHAMMAD KHANJANI, 3 SAEID MOHARRAMIPOUR, 1 AND MYRON P. ZALUCKI 4 Environ. Entomol. 39(1): 177Ð189 (2010); DOI: 10.1603/EN08239 ABSTRACT Immature survival and development of alfalfa weevil, Hypera postica (Gyllenhal) (Coleoptera: Curculionidae), were examined at 15 constant temperatures ranging from 9 to 37°C. At 9 and 37°C, eggs did not develop. Embryos developed to adulthood between 11.5 and 36°C, although survival was low at both ends of the temperature range. Distribution of development times for all stages of alfalfa weevil were skewed toward longer times mainly at moderate temperatures. Constant proportion of time spent in egg, larva, and pupa indicated rate isomorphy within the range 14 Ð31.5°C. No signiÞcant difference was shown between development time of males and females at any of the temperatures tested. Two linear and 23 nonlinear models were Þtted to describe development rate of immature stages of H. postica as a function of temperature, as well as estimating the thermal constant and critical temperatures (i.e., T min ,T opt , and T max ). There was no statistical difference between the estimated parameters, using Ikemoto and ordinary linear methods. Of the nonlinear models Þtted, the Logan-6/Lactin-2, Analytis-3/Briere-2, and Analytis-3/Briere-2 models were found to be the best for modeling development rate of egg, larva, and entire immature stages of H. postica, respectively. Our Þndings will be incorporated in more efÞcient phenological models of this pest and its population dynamics. KEY WORDS alfalfa weevil, immature survival, development time, rate isomorphy, modeling Alfalfa, Medicago sativa L., is the worldÕs most valuable cultivated forage crop. It is annually attacked by a very destructive pest, the alfalfa weevil, Hypera postica (Gyllenhal) (Coleoptera: Curculionidae) (Metcalf and Luckman 1994). The feeding damage inßicted by the alfalfa weevil, as an important early-season defo- liator of the crop, sometimes is so devastating that many growers give up trying to harvest (Khanjani 2008). Of Eurasian origin, since its Þrst report in the eastern United States in the mid-1940s, the species has become a key pest around which various pest man- agement systems have been developed (Kuhar 2000). It is well known that different geographic regions have unique problems because the weevilÕs biology and management requirements are dependent on climatic factors, which vary from region to region (Roberts et al. 1970, Kuhar et al. 2000). Temperature has a direct inßuence on the key life processes of survival, development, reproduction, and movement of poikilotherms and hence their popula- tion dynamics (Price 1997). Temperature sets the lim- its of biological performance in arthropods; the low and high temperature thresholds and optimal temper- ature can be considered for all major life processes, where within a speciÞc range, a temperature change results in a proportional rise or fall of the rate of any given process (Roy et al. 2002). Evolution has ensured that the organismÕs development is appropriate to its environment; therefore, the thermal traits of organ- isms have been honed by selection to maximize their physiological Þtness in relation to the thermal envi- ronment to which they are adapted (Trudgill et al. 2005). The variability of thermal characteristics may be studied among species (Honek 1999), populations (Lee and Elliott 1998), developmental stages (Honek and Kocourek 1990), and with other ecological factors such as food source, speciÞcally when the develop- mental conditions are adverse (Golizadeh et al. 2007). Although the idea of using ambient temperature and time to describe development of cold-blooded animals is 270 yr old (Reaumur 1735 cited in Young and Young 1998), early attempts to relate temperature to insect development go back to the work of Sand- erson (1910) and Glen (1922) on Cydia pomonella L. Subsequently, a variety of rate functions or models have been proposed to describe the relationship be- tween temperature and arthropod development (Ludwig 1928, Janisch 1932, Davidson 1942, Pradhan 1945, Stinner et al. 1974, Logan et al. 1976, Analytis 1977, Sharpe and DeMichele 1977, Lactin et al. 1995, Briere et al. 1999). They vary with respect to param- 1 Department of Entomology, Faculty of Agriculture, Tarbiat Mo- dares University, PO Box 14115-336, Tehran, Iran. 2 Corresponding author, e-mail: fathi@modares.ac.ir. 3 Department of Plant Protection, Faculty of Agriculture, Bu-Ali Sina University, Hamedan, Iran. 4 School of Integrative Biology, University of Queensland, St. Lucia, Queensland 4072, Australia. 0046-225X/10/0177Ð0189$04.00/0  2010 Entomological Society of America