Spiders in Vineyard Agro-Ecosystems

Two workgroup sessions on “Spiders in Vineyards” were held during 1994 (CSU Fresno-March, UC Kearney Ag Center-October), providing outstanding opportunities for information exchange and research coordination. Round-the-clock spider sampling studies (6A, 12N, 6P, 12M) conducted near Madera indicated that overall, spiders as a group were collected (canopy shake technique) equally well at any time of day. Spiders were sampled during the unorthodox fall / winter season of 1993-94 at Ripperdan (Madera County) using pitfall traps and cardboard banding (to our knowledge, no other researchers in California have sampled spiders using this field protocol during the winter). Studies focusing on direct observation of Trachelas and Cheiracanthium behavioral ecology in vineyards provided 31 hours of nocturnal field viewing time, only 20%of which resulted in successful spider sightings. Of this total spider viewing time, over 92% involved Cheiracanthiunr, Trachelas comprised only 8%. Daytime leaf sampling data revealed that the small theridiid spider Theridion constituted over 2/3 of all spiders observed during 1994. Field researchers were mildly surprised to find the well-known clubionid spider Cheiracanthium frequenting malaise traps placed on vineyard trellis crossbars which were designed primarily to sample populations of parasitic insects. A total of 10 Cheiracanthium spiders (7 females and 3 juveniles) were found in the malaise traps; no other spider species were found in the malaise traps at any time during 1994.