Submitted to: Crop Protection Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 28, 2008
Publication Date: February 20, 2009
Citation: Cabanillas, H.E., Jones, W.A. 2009. Pathogenicity of Isaria sp. (Hypocreales: Clavicipitaceae)against the sweetpotato whitefly B biotype, Bemisia tabaci (Hemiptera: Aleyrodidae). Crop Protection. 28:333-337. Interpretive Summary: The sweetpotato whitefly has become the world’s most damaging whitefly pest species. It is a major pest of economically important crops worldwide, especially in warm climates. It kills crops by sucking their sap, spreading viruses, and excreting a sticky substance called honeydew. The heavy use of chemical pesticides to control the whitefly is not always effective, as this insect has the ability to develop resistance to a wide range of pesticides. Because of the negative impact of pesticides on natural enemies of the whitefly, humans, and environment, sound alternative means of control are needed. Beneficial fungi are important biocontrol agents of these insect pests. Unlike other biocontrol agents, they infect by penetrating the external insect cuticle and need not be ingested to initiate disease. They continue to offer the only biological control option to control plant-sucking insects. An indigenous insect fungus, Isaria sp., was recently discovered on infected whiteflies feeding on eggplants during a severe epizootic of whiteflies in our greenhouse at Weslaco, Texas in 2001. Since then, it has periodically wiped out whiteflies at this location. Laboratory tests showed that this fungus is able to kill larval and adult whiteflies. The average time to kill 50% of whiteflies was estimated. In sprays on whitefly-infested plants (1000 spores/mm2), this fungus killed second instars in three days and third instars in four days. Adult whiteflies became infected after delayed infections of whiteflies treated with this fungus. These findings will be immediately useful in the development of an effective product to help farmers, scientists and the industry in the control of whiteflies. Such biological control methods will reduce the need for insecticide use and associated environmental problems.
Technical Abstract: The pathogenicity of an indigenous entomopathogenic fungus, Isaria sp., found during natural epizootics on whiteflies in the Lower Rio Grande Valley of Texas, against the sweetpotato whitefly, Bemisia tabaci Gennadius biotype B, was tested under laboratory conditions (27 ºC, 70% RH and a photoperiod of 14:10 h light: dark). Exposure of second, third and fourth instar nymphs to 20, 200, and 1000 spores/mm2, on sweet potato leaves resulted in insect mortality. Median lethal concentrations for second instar nymphs (72-118 spores/mm2) were similar to those for third instar nymphs (101-170 spores/mm2), which were significantly more susceptible than fourth instar nymphs (166-295 spores/mm2). The mean time to death was less for second instars (3.0 days) than for third instars (4.0 days) when exposed to 1000 spores/mm2. Mycosis in adult whiteflies became evident after delayed infections of SLWF caused by this fungus. These results indicate that Isaria sp. is pathogenic to B. tabaci larvae, and to adults through delayed infections caused by this fungus. This fungus was found naturally infecting nymphs, pupae and adult stages of the sweetpotato whitefly in the Lower Rio Grande Valley of Texas, and can control B. tabaci under high temperatures in this semi-arid subtropical region.