Reliability of Degree-Day Models to Predict the Development Time of Plutella xylostella (L.) under Field Conditions.

The diamondback moth, Plutella xylostella (L.), is a cosmopolitan pest of brassicaceous crops occurring in regions with highly distinct climate conditions. Several studies have investigated the relationship between temperature and P. xylostella development rate, providing degree-day models for populations from different geographical regions. However, there are no data available to date to demonstrate the suitability of such models to make reliable projections on the development time for this species in field conditions. In the present study, 19 models available in the literature were tested regarding their ability to accurately predict the development time of two cohorts of P. xylostella under field conditions. Only 11 out of the 19 models tested accurately predicted the development time for the first cohort of P. xylostella, but only seven for the second cohort. Five models correctly predicted the development time for both cohorts evaluated. Our data demonstrate that the accuracy of the models available for P. xylostella varies widely and therefore should be used with caution for pest management purposes.

Thermal Requirements, Fertility, and Number of Generations of Neoleucinodes elegantalis (Guenée) (Lepidoptera: Crambidae).

The small tomato borer Neoleucinodes elegantalis (Guenée) (Lepidoptera: Crambidae) is one of the major pests of solanaceous in Central and South America. Little is known about the role of temperature on the biological traits of this species. Development time of the immature stages and longevity and reproduction of adults of N. elegantalis at constant temperatures (15, 20, 25, 27, and 30 ± 1°C) were determined when larvae were fed on fruits of the tomato hybrid "Paronset." Neoleucinodes elegantalis completed its life cycle at temperatures between 15°C and 27°C, indicating that it can remain active throughout the year in the subtropical region of Brazil. The temperature threshold (T t) was 8.8°C for the egg stage and 7.7°C for the larval and pupal stages. The small tomato borer required 588.2 degrees-day for its full development. At 30°C, the eggs were infertile, indicating that temperatures above 27°C are deleterious to the fertilization/embryonic development of the studied population of N. elegantalis. The number of generations of N. elegantalis per year in the Brazilian subtropical region is lower than for populations developing in warmer tropical areas. A relationship was found between the number of generations and the increase in latitude.