Marc Sporleder

A Temperature-Based Simulation Model for the Potato Tuberworm, Phthorimaea operculella Zeller (Lepidoptera; Gelechiidae)

Abstract The potato tuberworm, Phthorimaea operculella Zeller, is a serious pest of the potato, Solanum tuberosum L., in subtropical and tropical production systems around the world. Knowledge of the temperature-dependent population growth potential is crucial for understanding population dynamics and implementing pest control strategies in different agro-ecological zones. The development, mortality of immature life stages, and reproduction of P. operculella were studied at constant temperatures ranging from 10 to 32°C. The theoretical developmental thresholds were 11, 13.5, and 11.8°C, and required incubation times were 65.3, 165.1, and 107.6 degree-days (DD) for the egg, larval, and pupal stages, respectively. The nonlinear shape of the temperature–development curve at low temperatures was well described by the modified four-parameter Sharpe & DeMichele model. The log-normal function was fitted to the normalized cumulative frequency distributions of developmental times for each life stage. Temperature effects on immature mortality were described by polynomial regressions. The optimal temperature for survival was within the range of 20–30°C. Temperature effects on adult senescence were described by the modified Sharpe & DeMichele model. A polynomial function was fitted to total fecundity and temperature. Fecundity was highest around 21°C. Age-related cumulative proportions of fecundity were well described by a Gamma function. Most eggs were laid within the first quarter of the female life span. The established functions were used to build a P. operculella population model, and life table parameters were simulated over a range of temperatures. Calculations gave good predictions when compared with published data. Populations increase within a temperature range of 10–35°C, with an optimum at 28–30°C.

An improved method to determine the biological activity (LC50) of the granulovirus PoGV in its host Phthorimaea operculella

Granulovirus (PoGV) is a promising candidate to substitute for chemical insecticides in integrated pest management (IPM) of the potato tuber moth, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae). A procedure to assess pathogenicity (LC50) and its standardization is crucial for research into the use of pathogens as biocontrol agents. In the present study, an egg‐dip bioassay method was developed and its precision tested in a series of six bioassays over a time period of 18 months. Bioassays were carried out at 25 °C incubation temperature. The probit model as a statistical analysis method for the interpretation of concentration responses proved better than the exponential model. LC50 values ranged from 2.3 × 106 to 107 granules ml−1 with a mean of 5 × 106 granules ml−1 and regression slopes varied between 0.73 and 1.05 with a mean of 0.84. LC50 values and slopes displayed no significant differences according to their 95% confidence limits. The rate of harvested infected larvae showed a linear increase with increasing concentration on a log‐log scale. The mean natural mortality was 15% (SE ± 1.8%) and can be considered as a main factor producing variability among bioassays. The advantages of this bioassay method and its application in PoGV research are discussed.

Susceptibility of Phthorimaea operculella Zeller (Lepidoptera; Gelechiidae) to its granulovirus PoGV with larval age

1 Granulovirus PoGV is a strong candidate to substitute for chemical insecticides in integrated pest management (IPM) of the potato tuber moth Phthorimaea operculella Zeller (Lepidoptera: Gelechiidae). Generally, susceptibility to baculoviruses decreases with increasing larval age. For effective field applications, knowledge of the age‐related change in susceptibility is crucial.

Application and evaluation of entomopathogens in potato

More than 290 million metric tons of potatoes (Solanum tuberosum) are produced throughout the world annually. According to the FAO 2004–2005 statistics, China, Russia, India, Ukraine, and the United States rank 1–5, respectively, in potato production. Potato production ranks fourth among agricultural crops, after wheat, maize, and rice. In some regions, potato is grown as a dryland crop; in others, it is overheadirrigated with a traveling gun-type irrigation or a central pivot irrigation system. Furrow irrigation is seldom used.

A Temperature-Dependent Phenology Model for Liriomyza huidobrensis (Diptera: Agromyzidae)

Abstract Liriomyza huidobrensis (Blanchard) is an economically important and highly polyphagous worldwide pest. To establish a temperature-dependent phenology model, essential for understanding the development and growth of the pest population under a variety of climates and as part of a pest risk analysis, L. huidobrensis life-table data were collected under laboratory conditions at seven constant temperatures on its host faba bean (Vicia faba L.). Several nonlinear equations were fitted to each life stage to model the temperature-dependent population growth and species life history and finally compile an overall temperature-dependent pest phenology model using the Insect Life Cycle Modeling (ILCYM) software. Liriomyza huidobrensis completed development from egg to adult in all temperatures evaluated, except at 32 °C, which was lethal to pupae. Eggs did not develop at 35 °C. Mean development time of all immature stages decreased with increasing temperature. Nonlinear models predicted optimal temperature for immature survival between 20–25 °C (32–38% mortality of all immature stages). Life-table parameters simulated at constant temperatures indicated that L. huidobrensis develops within the range of 12–28 °C. Simulated life-table for predicting the population dynamics of L. huidobrensis under two contrasting environments showed that lowland temperatures at the coast of Peru (250 m.a.s.l.) presented better conditions for a potential population increase than highland (3,400 m.a.s.l.) conditions. The presented model linked with Geographic Information Systems will allow pest risk assessments in different environmental regions to support the regulation of pest movement to prevent pest entry into not-yet invaded regions as well as to implement effective management strategies.