| Using non-spatial statistical methods to determine distribution of insects in alfalfa fields |
| Paper ID : 1231-3IICE (R1) |
| Authors: |
|
mahsa Ghahramani *, Roghaiyeh Karimzadeh, Shahzad Iranipour Department of Plant Protection, Faculty of Agriculture, University of Tabriz, Tabriz, Iran |
| Abstract: |
| This study was conducted to determine distribution patterns and related parameters of spotted alfalfa aphid, Therioaphis maculata (Buckten), pea aphid, Acyrthosiphon pisum (Haris) and two coccinellid species (Coccinella septempunctata and Hippodamia variegata) in six alfalfa fields during two growing seasons of 2016 and 2017. All fields were divided into 20 × 20 m grids. Weekly sampling was started when alfalfa plants reached 10 cm in height, and continued until harvest. Two random samples per plot were taken by a 1 × 1 m quadrat, to count adult coccinellids. To sample the aphids, twenty alfalfa stems (longer than 10cm) per plot were removed randomly and shaken into a white pan for eight times; and fallen aphids were counted and recorded. Ratio of variance to mean as well as Taylor’s power law (TPL) and Iwao’s patchiness index (IPI) were used to determine the spatial distribution patterns of the insects. In all sampling dates, the variance exceeded the mean, which may imply an aggregative distribution. Aggregation was also confirmed by regression coefficient of TPL (parameter β) and coefficient of IPI (b), which both were significantly above unity. Based on the coefficient of determination (R2), the TPL provided a better description of the population parameters. On the other hand, covariance analyses showed that regression lines of the six alfalfa fields had same parameters (both slope and intercept) for all the studied insects. Therefore, the data of all fields were pooled and analyzed altogether. Similarity between aggregated distribution patterns of aphids and coccinellids indicated that there was a positive association between predator and prey in the fields. Using different statistical methods provided useful information about distribution and spatial pattern of insects and natural enemies in alfalfa fields, and this information can be used in conservation of natural enemies and biological control of pests. |
| Keywords: |
| Distribution patterns, aphids, Taylor’s power law, Iwao`s regression, aggregation |
| Status : Paper Accepted (Poster Presentation) |
