Mortality of Indianmeal moth (Lepidoptera: Pyralidae) populations under fluctuating low temperatures: model development and validation.

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.

Relationship between supercooling point and mortality at low temperatures in Indianmeal moth (Lepidoptera: Pyralidae).

Indianmeal moth, Plodia interpunctella (Hübner), is classified as a freeze-intolerant organism and one of the most cold-tolerant stored-product pests. The objective of this study was to determine the relationship between mortality at low temperatures after minimum exposure and the supercooling point (SCP) for laboratory-reared P. interpunctella at different stages of development. This relationship also was analyzed for field-collected, cold-acclimated fifth instars. Mean SCP of laboratory-reared larvae (i.e., feeding stage) was consistently above approximately -16 degrees C. Mean SCP of laboratory-reared pupae and adults (i.e., nonfeeding stages) and field-collected, cold-acclimated fifth instars was consistently below approximately -21 degrees CP seemed to be the boundary between survival and death for larvae. However, it seemed that a 1-min exposure was not sufficient to cause larval mortality at the SCP. Alternatively, for both pupae and adults, the SCP seemed not to play an important role in their survival at low temperatures, with significant mortality observed at temperatures higher than the mean SCP. Adults were the most susceptible to low temperatures with no survival occurring at -20 degrees C, > 3 degrees C above its mean SCP. Results of this investigation demonstrate that P. interpunctella has a different response to low temperatures depending on stage of development and cold acclimation. Classifying P. interpunctella only as a freeze-intolerant organism disregards the occurrence of prefreeze mortality in this species. Therefore, a reclassification of this species (e.g., chill tolerant or chill susceptible) based on the extent of prefreeze mortality and the temperature and time of exposure at which it occurs is suggested.

A simple method to adjust cooling rates for supercooling point determination.

A simple method to obtain predetermined constant cooling rates for insect supercooling point (SCP) determination is described. A transient heat transfer equation was used to design polystyrene cubes of different sizes to yield constant rates of cooling at their centers when held at a constant surrounding temperature. Cubes of 0.29 x 0.29 x 0.29 m and 0.19 x 0.19 x 0.19 m were found to produce cooling rates of about -0.5 and -1 degree C per min, respectively, from 0 to -40 degree C. The observed temperature variations at the geometrical center of the cubes were similar to those predicted by the equation. Temperature plots showed a nearly constant rate of cooling. Supercooling points of Tribolium castaneum (Herbst) at different stages of development were recorded using polystyrene cubes. These SCPs compared favorably with published values. This method of obtaining cooling rates is economical, flexible, and allows for multiple simultaneous SCP measurements.

Seepage from deep bedded and poultry litter systems.

The work reported indicates that there could be a potential of ground water pollution by NO3-N from turkey facilities built on both sandy and clay soils. At four different depths (30.54, 61.08, 91.62, and 122.16 cm), the NO3-N levels for the clay soil were 1572, 497, 66, and 28 ppm, and those for the sandy soil were 293, 425, 324, and 164 ppm, respectively. No significant P increases were observed but there did exist a significant increase of K in the topsoil for both clay and sandy turkey structures. The results show that swine hoop houses with less than three or four years of age may not pose a threat to groundwater pollution due to the leaching of nutrients. The only dairy feedlot sampled in this study, although it has been used for more than 20 years, did not show leaching of NO3-N and P. However, it did show a significantly elevated concentration of potassium in the topsoil, as compared to the background sample. More sites should be investigated to verify this.