Effect of Application Technology on Interactions Between Biorational
Insecticides,
Microbial Control Agents and Natural Enemies of Sweetpotato
Whitefly
The first objective of this project was to develop and
test bioassay techniques for all stages of SPWF and its key natural enemies,
and to use these methods to evaluate selectivity of biorational insecticide
formulations, especially insecticidal soaps and oils. A related goal was
to evaluate phytotoxicity of these materials.
We chose first to work with the whitefly and compared
the insecticidal and repellant properties of a soap, a mineral oil, and
a surfactant-like sucrose ester extracted from Nicotiana gossei
Domin., with a pyrethroid (bifenthrin) against silverleaf whitefly Bernisia
arnentifolii Bellows & Perring. An extract of seeds from the
neem tree Azadirachta indica A. Juss. was also used in some
tests. All materials tested by leaf-dip bioassay were highly toxic to young
a. argentifolii nymphs, but mineral oil and a synthetic pyrethroid (bifenthrin)
were more toxic to all whitefly stages and more repellent to adults than
the insecticidal soap or N. gossei extract. Residues of insecticidal soap
and N. gossei extract were toxic to adult whiteflies only
when wet.
The same materials were tested against all developmental
stages of key predators and parasitoids of B. argentifolfi. The
pyrethroid standard, bifenthrin, was toxic to all developmental stages
of Nephaspis oculatus (Blatchley).(Coccinellidae) and insecticide soap
was toxic to larvae, but not to adults, eggs or pupae. Mineral oil was
moderately toxic to eggs, but had no significant effect on other stages.
Mixtures of sucrose and glucose esters were innocuous to all life stages
of the beetle. Bifentrhin was also toxic topically and residually to adults
of the lacewings Chrysoperia rufflabris (Burmeister) and
Ceraeochrysa cubana (Hagen) and larvae of C. rufflabris,
but was not to eggs of either species or larvae of C. cubana.
At field concentrations, neem, mineral oil and insecticidal soap were generally
not toxic to larvae or adults of either species whether exposed topically
or to residues. Oil was toxic topically to eggs of both species but neem
and soap were not.
Bifenthrin was also the most toxic material tested
against immature stages of Encarsia pergandiella Howard (Aphelinidae).
Mineral oil dips also caused high mortality of immature parasitoids, and
mineral oil residues on plant prevented parasitization by the wasp. Neem
extract, insecticidal soap, N. gossei sucrose ester and the synthetic sucrose
ester had relatively little effect on E. pergandiella. The phenoxy juvenile
hormone analog, pyriproxyfen, also was innocuous to all stages of E pergandiella
at concentrations causing near 100% mortality to the whitefly host. However
significant reduction in subsequent emergence of E. fonnosa Gahan was observed
at the highest rate (1 mg ai/liter).
These results indicated that the use of bifenthrin
would be incompatible with biological control of whitefly by the coccinellid,
chrysopids and the aphelinid tested, and that considerable interference
with coccinellid activity could be expected from insecticidal soap, depending
on the timing of application. On the other hand mineral oil and especially
N. gossei extract could be used against whitefly with relative
impunity to the coccinellids, although oil could be deleterious to the
E pergandiella, depending on coverage. Pyriproxyfen
at concentrations tested proved to be effective against B. argentifolfi,
safe to E. pergandiella and E transvena, but
relatively toxic to E. fbanosa, especially pupae.
A household detergent was evaluated and proved to
be 4 times more toxic to B. argentifolii than insecticidal
soap. However, concentrations as low as 0.5% sprayed twice a week reduced
early tomato production, although later production tended to compensate
for the loss. Weekly spray intervals produced a less severe phytotoxic
effect. Similar experiments with mineral oil produced comparable results,
although at twice or more the concentration.
Another project objective was to evaluate techniques
of applying biorational control agents against SPWF Computerized image
analysis and a blue tracer dye technique confirmed that distribution of
spray deposit on tomato foliage from a tractor-drawn hydraulic boom sprayer
in the field, and a moving boom (chain-driven) table sprayer used on dense
canopied "Lanai" tomatoes in a greenhouse was comparable. Therefore the
table sprayer provided a good model of field application. More material
was deposited on leaves in the outer plant canopy than within the plant
interior. Best coverage on lower leaf surfaces was achieved with highest
flow rates and pressure. Air carrier and electrostatic systems were evaluated
in the field and the greenhouse, but no clear advantages were seen over
hydraulic systems.
Toxicity of mineral oil, and to a lesser extent,
insecticidal soap to B. argentifolii was greatly reduced
when applied with a Potter tower compared to a leaf dip. In contrast, bifenthrin
was equally toxic whether sprayed or dipped. Thus, coverage was more critical
to the functioning of oil and soap, which depend on topical activity, than
to bifenthrin with an internal mode of action. Even more dramatic differences
in the mortality response of E pergandiella sprayed-on residues
versus residues of mineral oil applied as a dip to glass pipettes in which
parasitoids were later confined. Residues applied by the latter method
were 7 times more lethal to the parasitoids whereas the toxicity of bifenthrin
was the same with either bioassay method. Parasitoids were killed when
they became entrapped in droplets of oil which they were able to avoid
on the sprayed leaf surface but not in the dipped pipette. Thus, low adult
parasitoid mortality could be expected from oil in the field.
We concluded that insecticides effective again B.
argentifolii differed in terms of compatibility its predators and
parasitoids, with broad-spectrum such as pyrethroids at one extreme and
sucrose esters on the other. Mineral oil and insecticidal soap were relatively
innocuous but could be deleterious to certain stages depending on concentration
and/or method of application. These results have been utilized in the field
and in greenhouses to optimize control obtained with biorational insecticides
and reduce negative impacts on natural enemies.
The consept of biorational control as a management system based on biological
control and other practices compatible with it, is gaining wide acceptance
and may someday be a reality many agricultural systems.
Selected Publications.
Liu, T. X. & P. A. Stansly. 1995. Toxicity of some biorational insecticides
to Bemisia argentifolfi (Homoptera: Aleyrodidae) on tomato leaves. J. Econ.
Entomol. 88(3): 564-568
Liu, T. X. & P. A. Stansly. 1995. Toxicity and repellency of some
biorational insecticides to Bemisia argentifolii on tomato plants. Entomol.
Exp. Appl. 74: 137-143
Liu, T. X. & P. A. Stansly. 1995. Oviposition by Bemisia argentifolii
(Homoptera: Aleyrodidae) on Tomato: Effects of Leaf Factors and Insecticidal
Residues. J. Econ. Entomol. 88(4) 992-997.
Liu, T. X. & P. A. Stansly. 1995. Deposition and Bioassay of Insecticides
Applied by Leaf Dip and Spray Tower Against Bemisia argentifolii (Homoptera:
Aleyrodidae). Pesticide Science. 44:317-322.
Vavrina, C. S., P. A. Stansly & T. X. Liu. 1995. Household Detergent
on Tomato:
Liu, T. X. & P. A. Stansly. 1996. Oviposition, development and survivorship
of Encarsia pergandiella adults (Hymenoptera:
Aphelinidae) in four instars of Bemisia argentifolii (Homoptera: Aleyrodidae).
Ann. Entomol. Soc. Amer. 89(l): 96-102.
Liu, T. X. & P. A. Stansly. 1996. Morphology of Nephaspis occulatus
and Delphastus pusillus (Coleoptera: Coocinellidae), Predators of Bemisia
argentifolii (Homoptera: Aleyrodidae). Proc. Entomol. Soc. Wash. 98(2):
292-300
Liu, T. X. & P. A. Stansly. 1996. Toxiological effects of selected
insecticides to Nephaspis occulatus (Coleoptera: Coocinellidae), a predator
of Bemisia argentifolii (Homoptera: Aleyrodidae). J. Appl. Entomol. 120,
00-00.
Liu, T. X. & P. A. Stansly. 1996. Pupal Orientation and Emergence
of some aphelinid parasitoids (Hymenoptera: Aphelinidae) of Bemisia argentifolii
(Homoptera: Aleyrodidae). Ann. Entomol. Soc. Am. 89(3): 385-390.
Liu, T. X., P. A. Stansly & 0. T. Chortyk. 1996. Insecticidal activity
of natural and systhetic sugar esters against Bemisia argentifolii (Homoptera:
Aleyrodidae). Journal of Econ. Entomol. 89:1233-1289.
Liu, T. X. & P. A. Stansly. 1996. Effects of Pyriproxyfen on Three
Species of Encarsia, Endoparasitoids of Bemisia argentifolii. Journal of
Econ. Entomol. 90(2): 404-411
Stansly, P. A. & T. X. Liu. 1996. Selectivity of Insecticides to
Encarsia pergandiella (Hymenoptera: Aphelinidae), endoparasitoid of Bemisia
argentifolii (Homoptera: Aleyrodidae). Bulletin of Entomological Research.
87: 525-531
Stansly, P. A. & T. X. Liu. 1995. Activity of Some Biorational on
Silverleaf Whitefly. Proc.
Fl. State Hort. Soc. 107: 167-172
Stansly, P. A., T. X. Liu and D. J. Schuster. 1995. The rationality
of biorational insecticides for control of the silverleaf whitefly (Bemisia
argentifolfi). Proc. Third Ann. Prog. Rev. 5-year National Res. & Action
Plan for Develop. Manage. & Control Method for Silverleaf Whitefly,
USDA-ARS p. 94.
Liu, T. X., P. A. Stansly, & J. M. Conner. 1996. Deposition of Spray
Material on Tomato Foliage as Influenced by Volume and Pump Pressure. Proc.
Fl. State Hort. Soc. 108: 212-216.
Stansly, P. A., T. X. Liu, D. J. Schuster & D. E. Dean. 1996. Role
of Biorational Insecticides in Management of Bemisia. In: Bernisia 1995:
Taxonomy, Biology, Damage Control and Management. Andover, Hants, UKD.
D. Gerling and R. T. Mayer, Jr. {Eds.} PP: 605-615.