Effects Of Entomopathogenic Nematodes on Pink Bollworm Mortality
T. J. Henneberry, ARS Western Cotton Research Laboratory, Phoenix
Steinernema riobravis Cabanillas, Poinar & Raulston infected pink bollworm Pectinophora gossypiella (Saunders), larvae over a temperature range of 15.6 - 38.0 ° C. Temperatures of 32.2 ° C and higher and exposure for 48 h or more often resulted in decreased numbers of nematode killed larvae with living nematodes and increased numbers of dead larvae with dead or no nematodes.
Pink bollworm has been of economic importance in Arizona and Southern California since the mid-1960s (Henneberry 1986). The need for a biological component in pink bollworm management systems has stimulated continuing interest in entomopathogenic nematodes. Under desert cotton growing conditions in the southwestern United States, unshaded surface soil temperatures in cotton fields early in the season may reach 60-66 ° C (Butler and Henneberry 1976). Thus, high temperature tolerance is a desirable characteristic for candidate nematode species for application in late spring or early summer.
We conducted studies to determine the effects of temperature on mortality of pink bollworm larvae from nematode penetration and infection by S. riobravis as criteria for determining their potential as biological control agents.
Materials and Methods
Pink bollworm larvae were from the Western Cotton Research Laboratory colony. S. carpocapsae Kapow strain and S. riobravis were reared at the Western Cotton Research Laboratory using the in vivo method of Lindegren et al. (1993). Infective juveniles of both species were used throughout the study. Tests were conducted in 15 by 100 mm plastic petri dishes containing a piece of 90-mm No.4 Whatman filter paper moistened with about 1 ml of water. All studies were conducted under laboratory conditions.
The effect of duration of temperature exposure on S. riobravis was determined by exposing Pink boll worm larvae (10 per arena) to 150 S. riobravis IJs per arena for 24, 48 or 72 h in temperature cabinets at 26.7, 32.2, 35.6 and 38.0° C. Controls for each temperature were bioassay arenas with pink bollworm larvae only. The experiment was replicated five times. All larvae were dissected after the exposures and numbers of larvae with living or dead nematodes were recorded. Numbers of adult nematodes were recorded to determine infection and IJ development to the adult stage.
Data were analyzed using analyses of variance (MSTAT-C 1988) and means were separated using the least significant differences method only when a significant "F" test was obtained. All percent mortality data were arsenic transformed.
Temperature did not affect mortality of pink bollworm larvae in the untreated controls (Table 1). Mortality of S. riobravis (150 IJs per bioassay container) treated pink bollworm larvae ranged from 96.0 to 100.0% and was not affected by temperature or exposure time. Mortalities in all S. riobravis treatments were significantly greater than in untreated controls (F = 871.7, df = 6,92, P less than or equal to 0.01). Numbers of dead nematodes in pink bollworm cadavers were higher at 72 h at all temperatures than at 24 or 48 h (F = 3.77 , df = 6, 44, P less than or equal to 0.01) (Table 2)
S. riobravis infected pink bollworm larvae over a temperature range of 26.7 to 38.0° C. Exposures of 24 to 72 h at 26.7 to 32.2° C had no effect on pink bollworm larval mortality caused by S. riobravis. S. riobravis may be effective for Pink bollworm biocontrol under the late spring-summer hot, dry conditions of Arizona.
This is a part of publication
AZ1006: "Cotton: A College
of Agriculture Report," 1998, College of
Agriculture, The University of Arizona, Tucson, Arizona,
85721. Any products, services, or organizations that are
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Arizona. The University is an Equal
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