Tuesday, December 12, 2006

Activity cycles and vertical stratification of spiders in cornfields

Ryan Homsher, ryan_homsher@hotmail.com, Miami University, Department of Zoology, Oxford, OH and Alan Cady, cadyab@muohio.edu, Miami University - Middletown, Department of Zoology, Middletown, OH.

Spider distribution and abundance across the diel period has been investigated in various row crops but is not well-studied in corn. It is unknown whether certain families or groups of spiders prefer specific locations on corn plants, or if spiders change position over the diel period or across the season. Thus, a nine-week observational study of spiders on and around corn plants in six one-half hectare conventionally-tilled corn fields was conducted to determine daily spider activity cycles, their positions on the plants, and the composition of spider assemblages. Most variability of spider numbers and their community compositions appeared to be related to their phenology and corn growth stages. There was a well-defined stratification of spider families on the corn plants. The Lycosidae dominated the ground layer while the Salticidae were most prevalent on the plant tops throughout the season. Other spider families occupying the plants shifted their location during the summer. Web-building spiders (Theridiidae, Tetragnathidae) were sensitive to changing corn plant structure as the growing season progressed. Salticid and thomisid numbers on the plants were inversely related. There was evidence for interactions among foliage-running spider families, but they seemed not to impact web-building spiders. Most spider activity was at night. Lycosids and linyphiids contributed most to a mid-day activity spike early in the season. Salticids and theridiids added to this peak later on. No significant effects on spider numbers from the presence of straw refugia were found, but more lycosids tended to be near corn plants associated with refugia.

Species 1: Araneae Salticidae Phidippus audax
Species 2: Araneae Lycosidae
Species 3: Araneae Theridiidae