Submitted to: Program Review of Interagency Bemisia Classical Biocontrol Program in the U.S.
Publication Type: Book / Chapter
Publication Acceptance Date: 11/22/2004
Publication Date: 3/26/2008
Citation: Hoelmer, K.A., Roltsch, W.J., Simmons, G.S., Andress, E. 2008. Release and recovery of exotic natural enemies of Bemisia tabaci (biotype “B”) (Hemiptera: Aleyrodidae) in Imperial Valley, California. Program Review of Interagency Bemisia Classical Biocontrol Program in the U.S. Vol. 4:205-224
Interpretive Summary: The Imperial Valley , CA, is a region of year-round crop production of field and vegetable crops. In the early 1990's outbreaks of Bemisia tabaci [B strain] [=Bemisia argentifolii] occurred on in many cultivated crops including cotton, melon, cole crops, and many ornamental species. To increase the impact of natural enemies on whitefly and reduce the whitefly population, non-native aphelinid parasitoids were imported into the U.S. and released in Imperial Valley. Parasitoids released in Imperial Valley were mass produced at USDA-APHIS insectaries in California and Texas, by the Univ. of Arizona, and by the California Department of Food and Agriculture in California. Parasitoids were released in diverse settings such as gardens, urban areas and farm sites, commercial crops, and wildlife refuges. Surveys were conducted from1995 to 2001 to determine whether or not the introductions were successful. By 1998 to 2000, several exotic Eretmocerus and one Encarsia species had became common in recovery surveys. The most successful introduction was of a species originally found in the United Arab Emirates and Ethiopia in regions with climates similar to the Imperial Valley. By 2000, these parasitoids had been recovered from isolated desert sites surrounding Imperial Valley, providing additional evidence that establishment and dispersal of introduced species had occurred throughout the region.
Technical Abstract: The Imperial Valley , CA, is a region of year-round crop production of field and vegetable crops of approximately 500,000 acres. Bemisia tabaci Genn. [A-strain] has sporadically reached pest status since the early 1900's, but in the early 1990's outbreaks of Bemisia tabaci [B strain] [=Bemisia argentifolii Bellows & Perring] occurred on a broader range of host plants, including cotton, melon, cole crops and numerous ornamental species. To increase the impact of natural enemies on B. tabaci, non-native parasitoids in the genera Eretmocerus and Encarsia were imported and released into Imperial Valley during 1993-1999 to complement the indigenous natural enemy fauna. Parasitoids released in Imperial Valley were produced by mass rearing facilities of USDA-APHIS in Imperial, CA, and Mission, TX, Univ. of Arizona, Tuscon, AZ, and the California Department of Food and Agriculture in Sacramento, CA. Millions of several exotic species of Eretmocerus and Encarsia parasitoids were mass reared and released over successive years. Releases were made in managed field insectaries to provide continual availability of whitefly host plants through successive years, in urban areas on ornamental hosts, in commercial organic and low-pesticide input crops, in wildlife refuges, and in commercial plant nurseries. Release sites and procedures were designed to maximize the chances for establishment of parasitoids in the harsh climate of this desert region. Whitefly and parasitoid populations were monitored from 1995 to 2001 to determine whether or not establishment occurred. Surveys were conducted in long and short term insectary gardens, urban ornamental and garden plants, sentinel plant arrays, commercial cotton fields, and in surrounding desert areas. By 1998 to 2000, exotic Eretmocerus species became prominent in recovery surveys, often representing well over 50% of the local population. The predominant recoveries were of Eretmocerus emiratus / nr. emiratus which originated in the United Arab Emirates and in Ethiopia. DNA analysis indicated that the latter was dominant by 2001. Eretmocerus mundus and Er. hayati also appear to have established in lower numbers. One exotic Encarsia species, E. sophia, also became established from source populations originally collected in Pakistan and Spain. By 2000, introduced Eretmocerus spp. had been recovered from B. tabaci at widely separated desert sites to the east and to the west of the Imperial Valley, providing additional evidence that establishment and dispersal of introduced species had occurred. Although a larger number of species had been released, only a few species became well established although intensive efforts were made to promote their establishment. It is probable that the failure of the other species to establish was due to their being poorly adapted to this desert agricultural region.