Spiders in Vineyard Agro-Ecosystems

The overall goal of this research project is to continue to elucidate the ecological roles and potential economic value of spiders in vineyard agro-ecosytems. Specific objectives include: 1) To determine key behavioral habits and to study prey selection of both Cheiracanthium and Trachelas spiders, 2) To further investigate the diversity and abundance of spiders in vineyards, and 3) To develop a color field guide to important spiders in California vineyards. During 1995, spider research was conducted both in vineyards near Ripperdan (Grenache) and at CSU Fresno (Barbera, conventional and organic plots). Direct observation sampling in the grapevine canopy was conducted during evening hours (peak hunting activity periods for Cheiracanthium and Trachelas) using headband-mounted lights with red filters to avoid disturbing normal spider behavior. Another spider sampling technique used in 1995 involved placing corrugated cardboard bands around the base of vine trunks (particularly effective for Trachelas). Near the band locations, canopy shake samples were also conducted. Direct observation sampling involved a total of 26 hours viewing time in 1995. Only 8.3% of the total sampling time resulted in successful sighting of a Cheiracanthium or Trachelas spider. Frequency of occurrence data for the two spider genera mirrored results from 1994, in that 92% spider sightings were Cheiracanthium with the remaining 8% being Trachelas. Also similar to 1994 patterns, juvenile spiders were observed more frequently than were adults. Behavioral activities of Cheiracanthium spiders were rather diverse: adults hunting (25%), adults resting (25%), adults with egg sac/molting sac (8.3%), and juveniles hunting (54.2%). No Cheiracanthium were directly observed in the act of feeding on prey in 1995. Trachelas spiders were found in only two behavioral categories: juveniles resting (50%), and juveniles hunting (50%). Band trapping results at CSUF revealed the highest numbers of Trachelas adults in conventional plots in late January 1995, while Trachelas juveniles peaked in organic plots on the same date. Both adult and juvenile Cheiracanthium reached highest densities in late January in the organic plots. Band traps at the Ripperdan Ranch produced peak Trachelas adults and juveniles in late February 1995. Cheiracanthium adults at Ripperdan peaked throughout February, while juveniles reached highest densities in late February. Joint CSUF/UC collaboration (co-authors Mark Mayse, Michael Costello, Billy O’Keefe, Kent Daane, Curtis Sisk) on a color-illustrated field guide entitled, “Spiders in San Joaquin Valley Grape Vineyards” came to fruition in late 1995 with the guide’s publication. In addition, we are completing a translation of the guide’s text and caption information into Spanish to further expand the circle of effective contact for this publication; the translation will ultimately be included as a simple insert included in the basic color field guide.