Spatial Distribution of Phyllophaga implicita (Horn) (Coleoptera: Scarabaeidae) Larvae in Relation to Distance from the Adult Food Source

The spatial distribution of the Phyllophaga implicita (Horn) larval population in relation to the distance from the adult food source was investigated. Commercial soybean fields with 1 of 4 different shelterbelt arrangements were sampled in the fall of 1993, 1994, and 1995 to assess P. implicita distribution and density. Larvae were found only in fields with bordering shelterbelts. Ninety percent or more of the specimens were collected within 55 m of the shelterbelts. Exponential models indicated a significant relationship between larval density and distance from the shelterbelts, with densities declining as distance increased. Logistic regression analyses were performed to assess models for predicting the probability of finding larval infestations. A positive association between the probability of finding larvae (π_X) and the distance from the shelterbelt was found. With P. implicita having a 3-yr life cycle, the 1993 season was the flight year for the largest of the 3 broods. Sampling guidelines based on higher densities of larvae nearer the shelterbelts are discussed.