BIOLOGICAL CONTROL of RUSSIAN THISTLE

R. B. HAWKES R. D. GOEDEN * A. MAYFIELD D. W. RICKER

Russian thistle (Salsolu iberica Sennen harbors a variety of other insect pests Several species of insects attack Russian and Pau), a plant native to Eurasia, has such as lygus and stink bugs. These large, thistle in its native habitats, helping to become a widespread weed in California bushy “tumbleweeds” are common sights keep it at low levels. Among them is the and other western states. In these areas it on neglected or abandoned croplands, va- moth, Coleophora purthenka Meyrick (see serves as a favored alternate host plant cant residential and industrial lands, and photo), which is native to North Africa, for the beet leafhopper, Circlulifer tenellus highway and railroad right of ways. The the Middle East, and Asia. In the exten- (Baker), vector of the destructive “curly plants fracture at the base at maturity sive host plant specificity tests conducted top” virus of such crops as sugar beets, and scatter seeds as they are blown about with C. purthenica by Egyptian entomol- tomatoes, and melons. The plant also by the wind. Tumbleweeds fill irrigation ogists, by entomologists at the Common- and drainage canals, pile up against fence wealth Institute of Biological Control in and buildings, fill backyards and swim- Pakistan, and by entomologists at the ming pools, and startle motorists who en- USDA Biological Control of Weeds Lab- counter them while driving. Unsightly ac- oratory at Albany, California, C. purthe- cumulations of the dead, dry plants are nicu was found to be host-specific to her- not only difficult to remove, but also create baceous, annual species of Salsola and to fire hazards and traps for other wind- the closely related plant, halogeton (Hal- blown debris. ogeton glomerutus [M. Bieb.] C.A. Mey.) .

Egg of Coleophora parthenica. (30x1

larva of Coleophora parthenica in stem of Russian thistle. (10x1 Adult Coleophora parthenica. (12x1

CALIFORNIA AGRICULTURE, APRIL, 1975 3 The latter plant is a widespread, toxic 100 moths, about half of them females, range weed in several of the western were colonized at each site. states. During the spring of 1974, larvae were FOOD SYS Overwintering found to have successfully overwintered at the Coalinga and Tracy sites in Cali- Coleophora parthenica overwinters as fornia. However, no C. parthenica were mature larvae inside the stems of dead recovered at Bakersfield. Apparently one Russian thistle plants. The larvae pupate obstacle to the ready establishment of C. and the moths emerge in the spring. Mat- parthenica will be the scattering by the NVESTMENTS in the U.S. food and fiber ing occurs within 2-3 days. The small, wind of the tumbleweeds that contain the system from production through final straw-colored eggs are laid singly on the I overwintering larvae. The small, initial sales are so large that few of the indivi- leaves near the tips of branches (see colonies thus become too widely dispersed duals and firms comprising it can afford photo). The hatching larvae bore directly to allow the newly emerged moths to to leave their destiny to chance or indivi- into the leaves and then into the branches readily find mates. This situation oc- dual whims. Large-scale retailers and and stems where they complete their de- curred at Bakersfield during the winter food service firms require consistent sup- velopment (see photo). The fully-grown of 1973-74, when strong winds blew the plies at predictably uniform prices, as do larva cuts an exit hole in the stem, leaving infested plants away from the colonization the food manufacturing firms that supply only a thin layer or “windo~’~ofepidermis site. Infested plants may have to be con- them. Moreover, individual farmers with to cover the exit hole; it then retreats a tained overwinter by enclosures at some large capital investments cannot gamble short distance into its tunnel and pupates. locations until large field colonies have on future market outlets. At eclosion, the cream-colored moths been established, but eventually the The food industry, which should be force their way out of the stem through plant’s tumbling habit will aid in spread- viewed as a system, consists of all stages these windows. At least two generations ing the moths. in the production and supply of materials are expected annually in the San Joaquin used in agriculture, the production of Valley. An additional generation may oc- Additional releases commodities on the farm, processing of cur in parts of southern California. Ma- Additional releases of C. parthenica commodities, and the distribution of fin- ture larvae of the last annual generation moths from Pakistan were made by the ished products at retail stores and eating overwinter inside the dead plant stems as first author and cooperators in the late establishments. Because the system is SO noted. spring and early summer of 1974 near large and complex, improved coordina- Plants with moderate infestations of C. Indio, Boron, Lone Pine, Bakersfield, tion is badly needed. The use of contracts parthenica larvae observed in Egypt, Paki- Tracy, and Sacramento. Concurrent re- is essential for helping bring about this stan, and Turkey were somewhat stunted, leases of Pakistani or Turkish moths were coordination. had few branches, and had gnarled, thick- made at Chino, Colton, Moreno, Corona, ened basal stems. Samples taken by Egyp- Lakeview, and Rancho California by the Need for coordination tian entomologists throughout the 1973 second author and co-workers. An im- We have moved from a system of price- season showed an average of 44 larvae mediate goal of this project is to establish making at large terminal markets to per 100 stems at two study sites. Released strong field colonies of C. parthenica at prices based on decentralized or shipping from its own natural enemies during its these and other selected locations in the point marketing. Large-scale buyers of introduction to North America, C.purthe- state. Once this is accomplished (and if livestock and fresh fruits and vegetables nica should reach higher population den- the insect continues to show promise as a negotiate purchases directly at the ship- sities in California, which hopefully will biological weed control agent) , it will be ping point and bypass the terminal mar- cause sufficient stress to severely stunt, iE made available for general distribution ket except for emergency shortages. Pack. not kill, Russian thistle. to the many other areas where Russian ers sell processed fruits and VegetabIes During the spring of 1973, field re- thistle is a problem. directly to large-volume purchasers, un- leases of moths reared from overwinter- The California Department of Agricul- der somewhat loose terms of reservation ing larvae collected in Pakistan were ture partially funded the early research bookings that later may become actual made near Bakersfield, Cuyama, Coa- and development phases of this program sales. Broiler prices are negotiated be- linga, and Tracy in the San Joaquin Val- by the USDA; in 1974 the California tween large integrated operations and ley and also in Nevada, Utah, and Idaho. Division of Highways (Caltrans) con- large-scale retailers or buyers. Grain Limited numbers of moths reared from tinued the partial funding. These two prices are established in a complex mix- larvae imported from Egypt were liber- groups have also cooperated with the ture of organized exchange trading in ated at San Ysidro and Chino in southern USDA in site selection and manpower spot and future markets. Thus different California. The insects successfully com- needs. marketing practices have developed for pleted two generations during 1973 at different commodities. the Bakersfield, Coalinga, and Tracy R. B. Hawkes is Research Entwnol- As the agricultural and food industry sites, but establishment at Cuyama was ogist, and A. Mayfield is Agriculture Re- ias become industralized, it has devel- not determined. The Egyptian material search Technician, Biological Control of tped some common characteristics of in- failed to establish at either southern Cali- Feeds Laboratory, USDA-ARS, Western lustry, including trends towards separa- fornia location. Region, Albany, California. R. D. Goeden ion of capital, management, and labor ; In Idaho and Utah, the moths were is Associate Professor of Biological Con- pecialization of farming enterprises re- liberated in the open. At the California trol and D. W. Ricker is Staff Research ulting in purchase of production inputs; and Nevada locations, the moths were re- Associate, Division of Biological Control, ncreased applications of capital as sub- leased into large field cages containing Department of Entomology, University of titutes for labor; and increased depend- immature Russian thistles. From 30 to California at Riverside. ‘ace on science and technology. There is

4 CALIFORNIA AGRICULTURE, APRIL, 1975