Monitoring of the scale insect Icerya seychellarum (Westwood) infesting guava

The present study is on the spatial distribution and for estimating the optimum sample size for monitoring the populations of the scale insect Icerya seychellarum (Coccomorpha: Monophlebidae) on guava. The study was done in 2017–2018 and 2018–2019 in Luxor, Egypt. It was observed that the scale occurred year round and there were three to four peaks of seasonal activity: beginning of June, mid-September and mid-November in 2017 and the beginning of April, mid-June, mid-August and mid-October in 2018. Data on the indices of distribution and Taylor's and Iwao's regression analyses indicate significant aggregation behaviour. The regression models of Taylor's power law (b) and Iwao's patchiness (β) were both significantly >1, indicating that I. seychellarum had an aggregation distribution with a negative binomial distribution. The Iwao regression coefficients were used to determine the optimum sample size required to estimate populations at three fixed precision levels. The optimum size decreased with increased density in all levels of precision (5, 10 and 15%). These can be deployed to develop a sampling plan to estimate the population density accurately. Furthermore, the sampling protocol presented herein will be a tool for IPM decisions.