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Diseases
Microbial Insecticide
EIlXO(l messoria (Harris). 35
Several insect pathogens have been isolated from the diseased larvae of E. messoria
collected in the fields at Delhi, Ontario (Bucher & Cheng 1971). The bacterial diseases
are common and the bacteria most commonly isolated from infested larvae are Bacillus
cereus Frankland & Frankland, Enterobacter cloacae (Jordan), Enterobacter aerogenes
(Kruse), Klebsiella pneumoniae (Schroeter), Streptococcus faecalis (Andrewes
& Horder), Pseudomonas j1uorescens Migula, Pseudomonas spp., Bacillus splraericus
Neide, and Achromobacter spp. The infected haemocoels of cutworm larvae usually
contained one or a mixture of two or more bacterial species. B. cereus is a well-known
pathogen of many insects (Heimpel & Angus 1963); E. aerogenes and P. fluorescens
have been considered as potential pathogens of a number of insects (Bucher 1963); the
pathogenicity of the other species is very questionable and they probably occurred by
chance in the haemocoel of sick larvae of E. messoria. The microsporidial disease,
Nosema sp., is less common; the fungus disease, Sorosporella uvella (Krass.), is rare;
and the virus diseases are virtually absent.
Although larvae of E. messoria collected in the fields in Ontario are free from virus
diseases, they are susceptible to two virus diseases, nuclear polyhedrosis and
granulosis virus, originally isolated from a related cutworm, E. ochrogaster (Guenee)
(Bucher 1970). In cooperation with Dr. G.E. Bucher of Agriculture Canada Research
Institute, Belleville, Ontario, field tests using preparations of nuclear polyhedrosis
virus and granulosis virus were conducted in 1969 and 1970 at the Research Station,
Delhi, Ontario. These tests showed that both viruses would protect tobacco seedlings
from severe cutworm damage when applied on the green rye in high concentrations,
but they were less effective than chlorpyrifos (Dursban® or Lorsban l8l , Dow Chemical
of Canada Ltd.) treatment and better than the untreated control.
In 1971 and 1972, attempts were made to introduce both virus diseases into healthy
populations of E. messoria by spraying the virus suspensions on tobacco trap-plants
growing in a rye field. Consequently, a considerable number of E. messoria larvae
collected with tobacco trap-plants from areas where viruses were introduced in 1971
and 1972 were infested with virus. This indicated that a large amount of virus survival
occurred and that virus introduction is feasible. Unfortunately, this programme was
discontinued after the Research Institute, Belleville, Ontario, closed in the fall of 1972.
In 1969, laboratory experiments were conducted to determine the susceptibility of the
various larval stages of E. messoria in Ontario to four commercial preparations of
Bacillus thuringiensis Berliner: Thuricide® 9OTS, Thuricide® HP, Biotrol l8l BTB 183,
and Dipel® (Sandoz Canada). In these experiments, first-instar to third-instar larvae
that fed on rye leaves treated with all four B. thuringiensis preparations were found to
be susceptible at all rates applied (Cheng 1973b). Mortality of fourth-instar to seventhinstar
larvae fed treated tobacco leaves was low.
From the results of laboratory experiments, it was apparent that preparations of B.
thurittgiensis showed potential as a possible alternative to chemical insecticides for the
control of the early instar larvae of E. messoria. Therefore, a field test was conducted
in 1970 at the Agriculture Canada Research Station, Delhi, Ontario, to determine
whether these preparations could be as effective as chlorpyrifos for control of this pest
when applied on the rye cover crop in spring. Data showed that B. tlruringiensis
preparations as applied in the field for control of E. messoria larvae were relatively
ineffective as compared with chlorpyrifos (Cheng 1973b). The failure of these
preparations in the field trial is probably attributable to the different environmental
conditions and the much more complex ecosystem in the field than in the laboratory.