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58 H. H. Cheng
Evaluation of Control Attempts
Recommendations
Literature Cited
The most important insect parasitoids of the tomato homworm are Apanteles spp.,
which parasitize 10-20% of the hom worm larvae in tobacco fields each year.
Apanteles spp. kill the fourth-instar and fifth-instar larvae and essentially prevent
the homworm from causing maximum damage to the tobacco crop.
Preparations of B. thllringiensis control tomato hornworms as well as chemical
insecticides (Bucher & Cheng 1971. Cheng 1973. 1977b, 1978) and for approximately
the same cost of $20 to $25 per hectare for the material. B. thllringiensis has the merits
of being nontoxic to man. plants, and non-target animals including beneficial insects
such as parasitoids and predators. Thus it should be used by growers when an
economic population level of the tomato horn worm larvae occurs in the tobacco fields.
Under the present system of annual cropping of Due-cured tobacco in Ontario,
sequential applications of insecticides for homworm control and of sucker control
agents within short periods are common practices in tobacco production. To reduce the
cost of control measures, attempts have been made to mix recommended insecticides
and sucker control agents in the same tank and apply them to tobacco plants for
control of hornworms and suckers in one spray operation. Five year tests indicated that
all recommended insecticides used for homworm control can be mixed with sucker
control agents in the same tank before application without losing their efficacy and
caused no effects on the yield and quality of Due-cured tobacco in Ontario (Cheng 1977b,
1978, 1980).
At the Delhi Research Station, monitoring and economic threshold data have been
developed for M. qllinquemaculata (Cheng 1977a). Since this pest overwinters as a
pupa in the soil, early detection methods involve the capture of moths in light traps.
Larval densities are monitored from mid-July to mid-August and insecticide applications
are recommended when 5 or more large larvae (larger than 3 cm) are found per 100
plants. Generally. M. qllinqllemacillata can be controlled for the whole growing season
by a single application of B. thllringiensis or one of the recommended chemical
insecticides.
Detailed studies on the bionomics of the tomato hornworm in Ontario should be
conducted. Although preparations of B. thuringiensis have provided excellent control of
the hornworm larvae, the rapid drop of larvae from plants treated with chemical insecticides
is much more dramatic than the cessation of feeding and the slow death of B.t.infected
larvae. Growers, therefore, should be better informed ofthe merits of B. thuringiensis
to offset their natural preference for a chemical insecticide that has more
spectacular effects. A similar approach should be made in other areas of Canada where
the tomato hornworm is a problem.
Anonymous (1973) 1973 Tobacco production recommendations. Ontario Ministry Agriculture and Food, Pub!. 298. 32pp.
Begg, J.A. (1964) Microbial and chemical control of homworms attacking tobacco in Ontario. Journal of Economic Entomology 57, 646-649.
Bucher, G .E.; Cheng, H. H. (1971) Comparison of Bacillus Ihuringiensis preparations with carbaryl for homworm (Lepidoptera: Sphingidae)
control on tobacco. Canadian Entomologist 103, 142-144.
Cheng. H.H. (1973) Microplot test using microbial and chemical insecticides for control of tomato homworms on tobacco in Ontario. The
Lighter 43(3). 10-13.