Effects of malathion sprays on the ice plant insect system

A e r i a l application of malathion-bait sprays to eradicate the Mediterranean fruit fly in 1981 received considerable publicity because of its potential impact on nontarget organisms, primarily humans. We report here on studies showing the short-term effect these sprays had on a nontarget insect system, the accidentally introduced ice plant scale, Pulvinariella mesembryanthemi, and its native and introduced natural enemies. Ice plants, Carpobrotus spp., a r e grown extensively as ground cover associated with freeways, private residences, industrial parks and coastal areas. Since its detection in Napa, California, in 1971, ice plant scale has spread into 17 counties, threatening a large portion of the freeway landscaping maintained by the California Department of Transportation (Caltrans). During the past four years, Caltrans has funded the development of an integrated pest management program to allow continued use of ice plant without heavy reliance on insecticides. As an integral part of this program natural enemies of ice plant scale from South Africa have been imported and established (California Agriculture, September-October 19823. To date, two introduced parasitic Hymenoptera, Metaphycus funicularis and M. stramineus, and a coccinellid, Exochomus flavipes, have become established in northern California. An additional parasitic Hymenoptera, Encyrtus saliens, and a coccinellid, Hyperaspis senegalensis hottentotta, are currently being released. Several species of native (such as Coccophagus lycimnia) and previously established natural enemies (M. helvolus and Rhizobellius ventralis , i n t roduced against other pestiferous Homoptera) also attack ice plant scales. Substantial ice plant acreage in freeway landscaping was within the aerial malathion-bait spray zones in Santa Clara and Alameda counties. We monitored scale and natural enemy populations at a field site in Alameda County, the interchange of state routes 92 and 17 (Jackson Street, San Leandro), for six weeks before and eight weeks after a Jan A. Washburn 0 Richard L.Tassan 0 Kenneth Grace Eric Bellis 0 Kenneth S. Hagen 0 Gordon W. Frankie