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Chapter 17
Melanoplus spp., Camnula pellucida
(Scudder), and other Grasshoppers
(Orthoptera: Acrididae)
A.B. EWEN and M.K. MUKERJI
Grasshoppers have been important destructive pests since crop production began on the
Canadian prairies. Four species: the migratory grasshopper. Melanoplus sanguillipes
(Fab.); the twostriped grasshopper, M. bivittatllS (Say); the Packard grasshopper, M.
packardii Scudder; and the c1earwinged grasshopper, Camnllia pellucida (Scudder);
generally arc considered to be the most important. Natural enemies and weather
conditions cause marked fluctuations in their populations from year to year from one
area to another, and several population peaks have been recorded during the more than
thirty years that grasshopper surveys have been conducted in Saskatchewan (Gage &
Mukerji 1977). High populations and significant damage to crops have been associated
with early egg hatch due to an early, warm, and dry spring (Randell & Mukerji 1974).
Grasshoppers host a variety of pathogenic micro-organisms including fungi, bacteria,
viruses, and protozoans. Epizootics of fungal pathogens can produce drastic reductions
in grasshopper populations. Pickford & Riegert (1964) showed that Emomophlhora
grylli Fres. was a major factor responsible for significant reductions in grasshopper
populations, espciaJly C. pellucida, in Saskatchewan in 1963. Although there have
been other incidents of fungal epizootics, these pathogens have not given consistent
control of grasshopper populations because of their restrictive requirements of specific
moisture and temperature conditions for initiation and dissemination of infection in the
host populations (Henry 1970). Most bacteria associated with grasshoppers are
facultative pathogens which cannot multiply in the host gut but require direct passage
into the haemocoele (Bucher 1960). Also. bacteria and many of the fungi pathogenic in
grasshoppers are not suitable microbial control agents because they are associated
with or pathogenic in other insects and animals (Henry 1970).
Viral and protozoan pathogens have received more attention as potential biological
control agents for grasshoppers. An entomopox virus (Henry & Jutila 1966) and a
crystalline-array virus of the picornovirus group (Jutila et al. 1970) have been isolated
from M. sangllinipes and M. bivittatus, respectively. Although these viruses arc
uncommon in grasshoppers under normal conditions, observations indicate that they
may be capable of lowering the population density of their hosts. Prolonged effects of
these pathogens have yet to be assessed. Of the protozoans, Malameba locustae (King
& Taylor), several species of grcgarincs, three species of Nosema (N. locuslae Canning.
N. acridophagus Henry, and N. cuneatum Henry), and a number of other microsporidians
have been reported or described in grasshoppers. Malameba locustae and the
gregarines (the most common protozoans in grasshoppers) cause chronic infections but
have little immediate effect on their hosts.
Most research effort in recent years has been directed towards using the Nosema
spp. as biological control agents for the management of grasshopper populations and,
of these. N. loclIstae has received the most attention. In 1980 a quantitative study of
the effect of N. /ocuslae as a control agent against grasshopper populations was
carried out in a short grass pasture in east central Saskatchewan (Ewen & Mukerji
1980). The predominant grasshopper species were M. sangllinipes, M. packardii. and
C. pellucida, and about 50% of these populations were infected between 4 and 5 weeks
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