|
| Rural Industries |
Objectives
Background
Loopers are caterpillar species which are able to
defoliate a wide range of crops, such as grain legumes, oilseeds,
tobacco, vegetable crops and ornamentals, but are frequently inadvertently
controlled by chemical sprays directed at other pests, such as
Helicoverpa spp.
The development of more selective pest management
strategies (with increased reliance on biological control), while
highly desirable, is likely to allow loopers to escape from current
constraints and elevate them to a more serious pest status. The
use of conventional insecticides against loopers could then disrupt
effective biocontrol, particularly parasites and predators.
Baculoviruses are exclusively pathogens of arthropods and usually infect a narrow range of hosts. Baculoviruses are prime candidates for looper biocontrol, as their hosts feed openly on foliage rather than in concealed locations, and the viruses would be compatible with other biocontrol agents in an IPM program.
Research
The virus morphology, tissues infected and symptomology
were studied in C. argentifera. The age-related susceptibility
of C. argentifera larvae was determined by laboratory bioassay.
In addition, the virus was assessed for infectivity for larvae
of the taxonomically related species, C. eriosoma, Diachrysia
orichalcea, Heliocoverpa armigera, H. puntigera, and Spodoptera
litura. Optimum conditions for virus production were determined
by quantifying virus yield in larvae infected at different ages.
Potted bean and tobacco plants were infested with loopers and sprayed with virus to determine primary levels of infection. The behaviour and food consumption of treated and untreated larvae was recorded. Field plots of soybeans were sprayed with graded rates of virus, and larval mortality and virus persistence was recorded.
Outcome
The virus was highly potent for neonate C. argentifera.
Susceptibility decreased with increasing age, however an increase
in food consumption with age was found to compensate for developmental
resistance for larvae up to seven days old. The virus was infective
for both C. eriosoma and D. orichalcea, however
neonates of both species were less susceptible than those of C.
argentifera. The H. armigera, H. puntigera and S.
litura neonates were not susceptible.
Larvae died on average seven days after infection,
however food consumption and general activity declined rapidly
after three days. Neonates were the most efficient producers of
virus, but maximum yield per larva (2.2 x 10 10 PIBs)
was obtained from larvae infected and six-day-olds.
Virus applied to field plots of soybeans at a rate of 1.9x10 11 PIBs/ha gave >5% mortality. However, the virus was readily inactivated on the crop, with 40% mortality recorded at two days post-spray and <5% at four days post spray.
Implications
The looper virus shows potential as a looper-specific,
non-disruptive biocontrol agent compatible with all other insect
control agents and should be used as part of an IPM program. The
future use of the virus is dependent on the severity and regularity
of the looper problem in the future, which in turn depends on
agricultural practices that allow looper infestations to develop,
and the effectiveness of natural biocontrol.
RIRDC Project No: DAQ-126A
RESEARCHERS: Dr Robert Teakle and Chris Monsour
ORGANISATION: Cooperative Research Centre for Tropical Pest Management
Gehrmann Laboratories UNIVERSITY OF QUEENSLAND QLD 4072PHONE: 07 365 1851
FAX: 07 365 1855PUBLICATIONS:
Monsour, C J, Teakle, R E and King, C J (in preparation) Susceptibility of the tobacco looper, Chrytsodeixis argentifera, to a nuclear polyhedrosis virus.
Last updated: 10 October 1996
Copyright © RIRDC
Index of RIRDC Projects URL
http://www.rirdc.gov.au/pub/compendium/93-94/index-b.html