Prediction of the Annual Generations of The Fall Armyworm, Spodoptera frugiperda (J.E. Smith) at Maize Crop Using Accumulated Heat Units in South Egypt

The fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae), is among the dangerous pests infesting maize plants in Egypt. The purpose of this work was to estimate the approximate numbers, appearance date, size of the generations, and peaks of S. frugiperda on maize plants in Esna district, Luxor Governorate, South Egypt, throughout two corn seasons (2021 and 2022). As well as the prediction of their forecasted peaks using thermal units accumulation. This was done by examining the relationship between the population seasonality of S. frugiperda and the accumulated heat units expounded as degree days (DD's). The acquired results detected that S. frugiperda had three generations per season in the field conditions at Luxor Governorate. These generations were achieved on July, 7^th, August, 4^th and September, 1^st, during every season. These generations lasted 4, 6, and 4 weeks, respectively. The densities of these generations were 45.00, 82.88, and 55.88 larvae per 10 plants during the first season, respectively. But, during the second season, it was 43.88, 77.99, and 58.80 larvae per 10 plants, respectively.  In general, the second generation was the longest and bigger in size than the other generations throughout the two seasons.
           There was a positive association between the cumulative number of S. frugiperda larvae per 10 plants and the accumulated heat units over the two seasons. As well, the results mentioned the occurrence of three actual peaks that took place on (June, 7^th, July, 4^th, and September, 1^st) and four prospective peaks that took place on (July, 4^th, July, 23^rd, August, 10^th, and August, 27^th) during the first season. However, across the second season, there were four expected peaks that occurred on (July, 5^th, July, 24^th, August, 11^th, and August, 31^st), respectively. Additionally, by using obtainable weather data in the Luxor region, the expected peaks of larvae generations could be revealed when the accumulated thermal units attained 364.83 ± 9.36 DD's degree days.