Spatial distribution of alfalfa leaf weevil, Hypera postica (Col.: Curculionidae) in Urmia
Subject Areas :
Keywords: spatial distribution, Hypera postica, Alfalfa leaf weevil, aggregation indices, Iwao's regression model, Taylor's power law,
Abstract :
Alfalfa Medicago sativa (Linnaeus) is a forage plant that plays important role in mankind life by providing feed for domestic animals, stabilization air nitrogen, reducing soil erosion etc. Alfalfa leaf weevil (ALW), Hypera postica (Gyllenhal) is a great threat for this valuable crop. Knowledge about the pest distribution and life cycle leads to better understanding about relationship between pest and its habitat. It also provides basis for interpretation of dispersal patterns, population growth models, and pest management measures. Therefore, spatial distribution of ALW was surveyed in Urmia, Azarbaijan-e-Gharbi province in 2013. In this survey, cluster systematic sampling design was adopted. Sampling was carried out by a 0.25 m2 quadrate once a week. Plants within a quadrate consisted one cluster of overall 12 clusters of each sample. Sample means and variances were calculated for each date separately and aggregation indices as well as Taylor's and Iwao's regression models were used to identify distribution patterns of ALW in both sampling levels of a plant and a quadrate. Furthermore, goodness of fit test was used for the same purpose in the plant level. A peak of 102 larvae /m2 was occurred at 9 April. Different analyses led to different results in regards of spatial distribution patterns of ALW. Per plant estimates of mean and variance were very close to each other in all samples, suggesting a random distribution. They diverged however in quadrate level implying quadrate to be the main source of variation; a result confirmed also by One-way ANOVA. Both Taylor and Iwao's regression models delineated random distribution based on data of overall dates in both sampling levels. Aggregation indices as well as goodness of fit test however revealed weak to intermediate degrees of crowding at least in half samples. Nevertheless, no evidence of aggregation was present in first and last sampling dates.
