M. A. Carrillo

Cold Hardiness of the Multicolored Asian Lady Beetle (Coleoptera: Coccinellidae)

Abstract A classical biological control agent, Harmonia axyridis (Pallas), is having both beneficial and detrimental impacts in North America. The objective of this study was to evaluate the cold hardiness of H. axyridis in North America. Supercooling points and survival at subzero temperatures of field-collected and insectary-reared H. axyridis were examined. The mean (±SE) supercooling points for eggs and pupae (i.e., nonfeeding stages) were −27.0 ± 0.18°C and −21.3 ± 0.52°C, respectively. The mean supercooling points for larvae and adults (i.e., feeding stages) were −14.17 ± 0.33 and −11.9 ± 0.53°C, respectively. Sex and color morph (i.e., red: f. succinea versus black: f. spectabilis) had no effect on the supercooling point of H. axyridis adults. Mean supercooling points of H. axyridis adults from Minnesota and Georgia were significantly lower during winter months than summer months. The mortality of H. axyridis increased significantly after individuals were exposed to temperatures below the mean supercooling point of the population. Supercooling point was a good predictor of cold hardiness. However, the cold hardiness of H. axyridis appears to be a poor predictor of its northern distribution.

Physiological Constraints on the Overwintering Potential of the Soybean Aphid (Homoptera: Aphididae)

Abstract The soybean aphid, Aphis glycines Matsumura, has a heteroecious, holocyclic life cycle. Soybean aphids overwinter as eggs, hatch in the spring, reproduce asexually, and undergo three or more generations on buckthorn, Rhamnus spp., before migrating to a secondary host such as soybean, Glycine max (L.) Merr. The ability of different soybean aphid life stages to survive low temperatures potentially experienced during fall or winter is not known. The objectives of this study were to determine the supercooling point (SCP) of various soybean aphid life stages and to determine the annual probability that winter temperatures within the North Central region of the United States would equal or fall below the mean SCP of soybean aphid eggs. Aphid eggs are considered the most cold-hardy stage; therefore, their SCP can be used as a conservative estimate for aphid overwintering mortality. In our study, eggs had the lowest mean SCP (approximately −34°C) among all life stages, whereas gynoparae and oviparae had the highest mean SCPs (approximately −15°C). During the winter, extreme low air temperatures are likely to reach or exceed the mean SCP of soybean aphid eggs in portions of northern Minnesota, northern Wisconsin, and the upper peninsula of Michigan. Thus, widespread successful overwintering in the northern United States and southern Canada is less likely than in Illinois, Indiana, Ohio, Iowa, southern Minnesota, southern Wisconsin, and the lower peninsula of Michigan.

Supercooling point of bean leaf beetle (Coleoptera: Chrysomelidae) in Minnesota and a revised predictive model for survival at low temperatures

Abstract Integrated pest management (IPM) programs for the bean leaf beetle, Cerotoma trifurcata (Förster), could benefit from an ability to forecast the magnitude and timing of early-season infestations. The objectives of this study were to examine the supercooling point (SCP) of adult C. trifurcata as an index of its cold hardiness, monitor overwintering survival, and revise an existing model used to predict the overwintering survival of this pest in wooded areas as a function of low-temperature accumulation. Within a year, the mean SCP of C. trifurcata ranged from −8.9 to −6.0°C. Soil temperatures dropped below the lowest mean SCP (i.e., −8.9°C) in only 2 of 11 yr (1994–2004). In-field survivorship studies showed that adult C. trifurcata successfully overwintered in Minnesota (34–59% survival). This species survived well in years when the existing model predicted zero or low survival. In contrast, our revised model predicted more closely the overwintering survival of this species in southern Minnesota. However, other overwintering mortality factors should be studied to improve our understanding of how well C. trifurcata overwinters in temperate regions.

Lower lethal temperature for adult male Diamesa mendotae Muttkowski (Diptera: Chironomidae), a winter-emerging aquatic insect

Abstract The supercooling point (SCP) and lower lethal temperature (LLT50) of male adult Diamesa mendotae Muttkowski (Diptera: Chironomidae) were determined from field-collected individuals. SCP determined using surface-contact thermometry did not differ statistically from previously reported values for a previous generation of this species. The LLT50 was determined by exposing individuals to −10, −15, −20, −25, and −30°C for one minute. Mean survivorship was 96.7, 91.2, and 71.2% for tests at −10, −15, and −20°C, respectively. Exposure to −25 and −30°C resulted in 100% mortality in all tests. Results show that males of D. mendotae are freeze-intolerant with a mean SCP of −21.6°C which is only 0.1°C lower than its linear interpolated estimated LLT50 of −21.5°C. Our results confirm that a low SCP, rather than freeze tolerance, is a mechanism that facilitates emergence and adult activity of this species during winter conditions. The implications of SCP and LLT50 with regard to life cycle dynamics are discussed.

Effect of sex and age on the supercooling point of the winter-active Diamesa mendotae Muttkowski (Diptera: Chironomidae)

Supercooling points (SCP) of adult Diamesa mendotae Muttkowski, 1915 (Diptera: Chironomidae) were determined at 3, 5, 9, 12 and 17 days post-collection. Supercooling points were recorded using surface contact thermometry and a cooling rate of ca. 1°C min−1. Female SCPs averaged −22.81, −23.76, −23.85, −23.65, and −20.87°C on each date post-collection and did not differ significantly. Male SCPs were statistically similar and averaged −21.75, −23.53, −23.68, −23.66, and −22.92°C on each date post-collection. Paired comparisons of female/male SCPs on each date post-collection did not show significant differences over time. The overall mean SCP of D. mendotae (−23.05°C) is substantially lower than values of −5.3°C and −5.7°C published for adults and larvae of Belgica antarctica Jacobs 1900 collected at Palmer Station (Antarctica) and −14.2°C for larvae of Paraclunio alaskensis Coquillett 1900 collected at Vancouver Island, British Columbia. In addition, the SCP of this species appears to be lower than that of other winter-active insect species reported in the literature. Although no adults survived after the SCP was recorded, further studies are necessary to determine if D. mendotae is a freeze-intolerant insect. Nevertheless, our results suggest that a low SCP could be used as a mechanism to facilitate emergence and adult activity of this species during winter conditions.

Overwintering Mortality of Indianmeal Moth (Lepidoptera: Pyralidae) in Southern Minnesota

Abstract Indianmeal moth, Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae), has been classified as one of the most cold-tolerant pests of stored grain. In this study, the supercooling point (SCP) of field-collected, cold-acclimated fifth instars was determined as an index of cold hardiness. In addition, mortality of laboratory-reared and field-collected, cold-acclimated fifth instars exposed to −10°C was measured to understand the ability of P. interpunctella to survive winter conditions. Finally, the overwintering mortality of this species in southern Minnesota was measured in grain bins filled with shelled corn. The SCP of field-collected, cold-acclimated fifth instars was approximately −24°C before their release in grain bins. Mortality of laboratory-reared fifth instars exposed to −10°C reached 100% after only 12 h, whereas the same percentage was achieved after 312 h for field-collected, cold-acclimated individuals. Overwintering mortality of P. interpunctella under field conditions reached 100% in all locations inside the grain bins; however, depth within the grain mass, location inside the grain bin, and the duration of exposure to outdoor conditions significantly affected the rate of mortality. A mathematical model for the overwintering mortality of P. interpunctella is proposed as a first step to forecast early season infestations under field conditions.

Mortality of Indianmeal Moth (Lepidoptera: Pyralidae) Populations Under Fluctuating Low Temperatures : Model Development and Validation

Abstract A model for predicting mortality of Indianmeal moth larvae [Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae)] under fluctuating low-temperature conditions was developed. The time and temperature combinations required to achieve 100% mortality of field-collected, cold-acclimated P. interpunctella larvae obtained from laboratory mortality experiments were used to develop the mortality model. Accumulation of mortality rate over time was called the cumulative lethality index (CLI). Complete mortality of insect populations would occur when CLI equals 1. Observed mortality of field-collected, cold-acclimated P. interpunctella larvae in five 76.2-T (3,000-bu) shelled corn bins located in Rosemount, MN, during the winters of 2003–2004 and 2004–2005 were used to validate the CLI model (i.e., mortality model). Excellent agreement between predicted and measured time to 100% larval mortality was observed. The CLI model would be useful for developing low-temperature aeration management strategies for controlling overwintering P. interpunctella in grain bins. In addition, this model will be useful when determining if additional control measures will be required as a result of above-seasonal ambient temperatures.

Effect of Broken Corn on Indianmeal Moth Survivability

Survivability of Indianmeal moth, Plodia interpunctella (Hubner), larvae fed a standard laboratory diet, whole corn with 0% broken kernels, whole corn with 5 to 7% broken kernels, and 100% broken corn kernels were assessed in our laboratory at 28oC, 65% RH, and 14 h light :10 h dark photoperiod cycle. A conventional low-oil yellow dent corn (about 3.9% oil content) and a highoil corn hybrid (about 7.7% oil content) were tested. Survivability was measured as the percentage emergence of pre-pupae, pupae, and adults at the end of the rearing period. For the standard laboratory diet, a mean ± SD of 97.5% ± 2.9 larvae survived. The mean ± SD percentages of larval survival for the conventional low-oil yellow dent corn were 6.7 ± 2.9, 63.8 ± 4.8, and 80.0 ± 14.7 for 0, 7, and 100% broken kernels, respectively. The mean ± SD percentages of larval survival for the highoil corn hybrid were 28.3 ± 12.6, 81.3 ± 4.8, and 100.0 ± 0.0 for 0, 5, and 100% broken kernels, respectively. Larval growth rate for high-oil corn was faster than for low-oil corn. Results indicate that cleaning corn before storage could reduce Indianmeal moth problems. Also, Indianmeal moth problems in high-oil corn varieties might be slightly greater than in corn varieties with normal oil levels.