Other entomopathogenic bacterial species have 
been found in Pseudomonas, Aerobacter spp., 
Cloaca spp. and Proteus, but have not been 
seriously considered for use in biological control 
of pest insects owing to their non-specificity. 
/\. Mode of action and host range. 
All entomopathogenic spore-forming bacteria 
produce endospores which allow them to persist 
in a dormant or quiescent state outside the 
intended host. Upon ingestion by a susceptible 
host the spores may germinate in the gut. In obli¬ 
gate pathogens in the genus Bacillus, the vegeta¬ 
tive cells produced by the germinating spores 
enter the hemocoel where they multiply rapidly, 
destroy certain tissues, and soon fill much of the 
cavity. Prior to death of the host, thick-walled 
retractile spores are formed which appear white 
through the integument, thus the name “milky dis¬ 
ease". The causative organisms of “milky dis¬ 
ease" are B. popllliae, B. lentimorbus, B. 
fribourgensis, and B. euloomarahae, and affect 
primarily beetle larvae of the insect order Coleop- 
tera. Following death, the host disintegrates and 
the spores are released into the soil. The mode of 
action of obligate pathogens of the genus Clostri¬ 
dia differs in that these bacteria multiply only in the 
gut and do not invade the hemocoel. 
The crystalliferous sporeformers (varieties of 6. 
thuringiensis), in addition to forming endospores, 
produce a proteinaceous parasporal crystal in the 
sporangium at the time of sporulation. The crystal 
contains an endotoxin capable of paralyzing the 
gut of most pest lepidopterous larvae (Fleimpel, 
1967) and some pest mosquito larvae depending 
on the B. thuringiensis strain (de Barjac, 1 978a, b). 
This material has b-^^en labeled as 6-endotoxin 
(Heimpei, 1967) and susceptible insects are killed 
by the toxic crystals (Fleimpel and Angus, 1963). 
In addition to its insecticidal properties, the intra¬ 
cellular proteinaceous crystal produced by S, thu¬ 
ringiensis apparently is capable of regressing 
tumors (Prasad and Shethna, 1975). In addition to 
the crystal, at least three other substances toxic to 
insects may be produced by various strains of 
crystalliferous bacteria. Following the nomencla¬ 
ture proposed by Fleimpel (1967) these are; a- 
exotoxin, an enzyme of the growing bacterium; 
phospholipase C, that breaks down essential 
phospholipids in ensect tissue; /3-exotoxin, a 
small, water-soluble, heat-stable nucleotide 
which is a structural analogue of ATP that inhibits 
DNA-dependent RNA polymerase (Sebesta and 
Florska, 1968) and kills larvae and pupae of Dip- 
tera and some Lepidoptera; and 7-exotoxin, an 
unidentified phospholipase that affects phospho¬ 
lipids, probably releasing fatty acids from the 
molecule. Thej6-exotoxin has been demonstrated 
to show toxicity to mammals, however, a number 
of varieties of B. thuringiensis do not produce the 
/3-exotoxin (Faust, 1975) and these varieties are 
being used in commercial formulations. 
6. cereus, a spore-forming facultative patho¬ 
gen, also produces phospholipase C in quantities 
sufficient to damage gut cells of susceptible spe¬ 
cies, thus aiding entry of the bacterium into the 
hemocoel (Fleimpel 1955; Heimpei and Angus, 
1 963). The non-spore-forming entomopathogenic 
bacteria are a heterogeneous group that usually 
infect insects only under extraordinary circum¬ 
stances. Although they occur in the gut of the host, 
they do not multiply readily there and probably do 
not produce enzymes ortoxins in sufficient quanti¬ 
ties to cause damage or to aid invasion of the 
hemocoel. They do, however, multiply in the 
hemocoel of the insect once they have invaded it 
(Bucher, 1 963). 
Clostridial pathogens were originally isolated 
from Malacosoma californicum (pluviale) 
(Bucher, 1957). Other than experimental infec¬ 
tions in other tent caterpillars and the possible 
presence of these bacteria in Thymelicus lineola 
(Heimpei and Angus, 1963) little is known about 
their host range. 8. thuringiensis and its varieties 
have been tested successfully against more than 
137 insect species from the orders Lepidoptera, 
Hymenoptera, Diptera, and Coleoptera (Heimpei, 
1967). Most of these pathogenicity tests have 
been conducted in the laboratory. The most sus¬ 
ceptible insects are those lepidopterous larvae 
having alkaline gut contents (pH 9,0-10.5) and 
enzymes which dissolve the crystals and release 
the toxin (Angus, 1956; Angus and Heimpei, 1959; 
Heimpei and Angus, 1959). 
8. cereus is a common, widely distributed soil 
saprophyte with an extensive host range including 
insect species from the orders Coleoptera, Hyme¬ 
noptera and Lepidoptera (Heimpei and Angus, 
1963). Its host range is also limited by the pH of the 
gut as a highly alkaline gut content can inactivate 
the toxic exoenzyme, phospholipase C (Heimpei, 
1955). 
The non-spore-forming bacteria attack a wide 
range of hosts from the Acarina, and the insect 
orders Coleoptera, Diptera, Hymenoptera, Isop- 
tera, Lepidoptera, and Orthoptera (Bucher, 1963). 
8. Methods of propagation and factors which 
influence effectiveness. 
The obligate pathogens, among species of 
Bacillus and Clostridium, arefastidiousorganisms 
that can be propagated in artificial media only with 
extreme difficulty. The commercial preparations 
of 8. popilliae produced in the U.S.A. are made by 
injecting or feeding bacteria to grubs of the Japa¬ 
nese beetle. The bacteria multiply to great 
numbers in the grubs and are recovered by grind¬ 
ing up the host. 
2 
