Population fluctuations and spatial distribution of Aonidiella orientalis in the south of Kerman

Document Type : Research Paper

Authors

• Somayeh Ranjbar ¹
• Peyman Namvar ²

¹ Plant Protection Research Department, South Kerman Agricultural and Natural Resources Research and Education Center, AREEO, Jiroft, Iran

² 2. Plant Protection Research Department, South Kerman Agricultural and Natural Resources Research and Education Center, AREEO, Jiroft, Iran

Abstract

Keywords

• Citrus pest
• Population changes
• Sampling method
• Distribution

Extended Abstract

Introduction

Aonidiella orientalis is one of the most important citrus pests in the south of Kerman, which causes damage to different citrus cultivars. This pest feeds on the sap of leaves and fruits. Its most active is in September and October. The proper control of this pest depends on the determination of the peak time of 1^st nymph appearance and the use of insecticides at that time. Determining the optimum time requires regular sampling of the pest population. Knowing the peak periods of the pest population and determining the most appropriate unit and size of sample provides its population density. This research was carried out with the objectives of 1) investigating the periods of population fluctuations of A. orientalis 2) determination of its spatial distribution and the optimal number of samples.

Materials and Methods

This study was conducted in a citrus orchard of grapefruit variety. Sampling was done from two growth stages, 1^st nymph and adult of A. orientalis Sampling methods were fruit, leaves, and branches. Spatial distribution of 1^st nymph and adult stages of A. orientalis was determined using Morista's, Taylor's, and Iwao distribution indices in the 2020-2022 years. The optimal number of samples was determined by the relevant equations using two precision values 0.25% and 0.1%.

Results and Discussion

Based on the results the pest activity started in mid-March and increased gradually, depending on weather conditions. The peak of A. orientalis population happened in mid-April, mid-May, and late September. The spatial distribution of 1^st nymphs on leaves and fruits was random based on the Taylor and Iwao index and it was Aggregative for adults. Both nymphs (1^st instar) and adult stages had a uniform and random distribution in the sampling of branches respectively according to the Taylor and Iwao index. The r² value obtained from the Iwao index was greater than Taylor's, therefore, the Iwao statistics were used to determine the spatial distribution. The number of optimum samples for 1^st nymphs on leaf, fruit, and branch sampling method was calculated at 24.61, 24.29, and 19.2, respectively with 0.25 accuracy. In three sampling methods, RV was close to 25 for nymphs (1^st instar) which is favorable for pest management programs, and 10 for adults which is proper for ecological studies.