Population density and spatial distribution pattern of Tuta absoluta (Lepidoptera: Gelechiidae) on different tomato cultivars.
One of the most important factors in a sampling and integrated pest management program is to know the population density and spatial pattern of the insects, especially the invasive ones such as Tuta absoluta (Meyrick) that cause a serious problem in tomato cultivation. Therefore, population density and spatial distribution pattern of T. absoluta was determined in Varamin region (Tehran, Iran) during two growing seasons of 2015 and 2016 on seven tomato cultivars ('Primo Early', 'Rio Grande', 'Cal JN3', 'Petomech', 'Early Urbana Y', 'Super Strain B', and 'Super 2270'). The T. absoluta density was estimated as active mines (with live larvae) and inactive mines (without live larvae) per plant, which, summed together, resulted in the total infestation (total mines per plant). In 2015, the highest mean number of total mines made by T. absoluta was on 'Cal JN3' (21.82 mines plant-1) and the lowest mean was on 'Early Urbana Y' (11.08 mines plant-1). In 2016, the highest and lowest mean population density of T. absoluta was observed on 'Cal JN3' (14.44 larvae plant-1) and 'Super Strain B' (4.60 larvae plant-1), respectively. The spatial distribution pattern of T. absoluta was determined by using Morisita's coefficient, Taylor's power law, and Iwao's patchiness regression method as well as dispersion index of variance-to-mean-ratio. The dispersion index indicated the aggregated pattern of spatial distribution in all tomato cultivars during both years. Taylor's and Iwao's models showed aggregated pattern of distribution on Primo Early' and 'Early Urbana Y', respectively, in 2015 and on 'Super 2270' in 2016. But, on the rest of cultivars, the pattern was determined random. Also, Morisita's coefficient revealed a random distribution pattern for T. absoluta in all of the sampling dates. The smallest optimum sample sizes were estimated with Taylors' coefficients. These results revealed that tomato cultivars affected the population density and spatial distribution pattern of T. absoluta. The coefficients of the spatial pattern can be used for improving the sampling program to estimate the population density of T. absoluta accurately.