CRICKETS AS MODELS FOR INSECT IMMUNOLOGY
Shelley A. Adamo
Dept. Psychology and Neuroscience
Dalhousie University, Halifax, NS Canada
e-mail: sadamo@dal.ca
Advantages
The crickets (Family: Gryllidae) are a group of orthopteran insects consisting of
over 2,000 species (Walker and Masaki, 1989). Many species are large, abundant, and
easy to maintain in culture, making them convenient for behavioural and physiological
studies.
There is a large body of literature describing the basic physiology and behavior of
crickets (e.g. Huber et al., 1989). This background information is important for
understanding how immune systems are integrated with behavior. It allows researchers
to design experiments testing critical concepts without first having to perform a large
number of background studies. Crickets are also one of the few insects for which there is
a body of work describing their behavior in the field (e.g. lifespan in the field, Murray
and Cade, 1995). This information is especially important for studies in ecological
immunology. Crickets are also a standard model for neuroethological studies (e.g. Huber
et al., 1989), and this makes it possible to examine the link between immune systems and
nervous systems in this group. At present, the best methods for demonstrating such a link
(e.g. a combination of pharmacology and electrophysiology) are still easiest using larger
insects such as crickets.
Crickets can also be used to study how and why the development of the immune
system is sensitive to environmental influences (e.g. Jacot et al., 2005). Because they are
hemimetabolous insects, changes in immune function during development are less
complex than they are in other insects. In holometabolous insects such as dipterans and
lepidopterans, the large concomitant changes in an animal’s morphology, behaviour and
ecological niche that occur after metamorphosis mean that changes in immune function
between the larval and adult stage can have a number of interpretations. This complexity
makes it difficult to explain the sensitivity of the immune system to environmental
effects.
Disadvantages
Crickets are not model genetic organisms like Drosophila melanogaster.
Therefore, some techniques are much more difficult to develop for crickets than for other
organisms. Nevertheless, researchers have used modern molecular techniques, such as
RNAi, in crickets (Meyering-Vos and Müller, 2007).
Unfortunately, many crickets have hemolymph that coagulates very rapidly. A
variety of anti-coagulants are available (e.g. da Silva et al., 2000). However, the
chemicals that are often used to retard coagulation (e.g. ethylenediaminetetraacetic acid
(EDTA), and protease inhibitor cocktail) make some studies on hemocytes very difficult
to perform. Partly because of the problems raised by their sticky hemolymph, and partly
because they are not major agricultural pests, the immune systems of crickets are
relatively understudied. Available evidence suggests that their immune system may
differ substantially from that of other groups, such as the dipterans and lepidopterans.
For example, orthopterans do not appear to have the same antimicrobial peptides as other
insects. In fact, Hoffmann et al. (1996) speculates that they may not have antimicrobial
proteins at all, but may rely on lysozyme-like enzymes instead. Although it is clear
crickets have more than lysozyme-like enzymes in their hemolymph (e.g. Adamo, 2004),
whether they have antimicrobial peptides remains unknown. The lack of understanding
about their basic immune function limits the type of immunological studies that can be
done using crickets. However, information is growing about their immune function.
Summary
Many cricket species are large insects, with robust behavior and physiology.
Entomologists have taken advantage of these traits and crickets have been well studied in
some areas (e.g. Cricket Behavior and Neurobiology, eds. Huber, Moore and Loher,
1989). They are one of the few insect groups in which there has been substantial research
on their behavior in the field. For these reasons, they are attractive models for studies in
ecological immunology and for studying the interactions between the immune system and
other physiological systems.
References
Adamo, S.A. (2004) Estimating disease resistance in insects: phenoloxidase and
lysozyme-like activty and disease resistance in the cricket Gryllus texensis. Journal
of Insect Physiology, 50: 209-216.
Da Silva, C., Dunphy, G.B. and Rau, M.E. (2000) Interaction of hemocytes and
prophenoloxidase system of fifth instar nymphs of Acheta domesticus with bacteria.
Developmental and Comparative Immunology, 24: 367-379.
Hoffmann, J.A., Reichert, J. and Hetru, C. (1996) Innate immunity in higher insects.
Current Opinion in Immunology, 8: 8-13.
Huber, F, Moore, T.E. and Loher, W. (1989) Cricket Behavior and Neurobiology. Cornell
University Press, Ithaca, NY.
Jacot, A., Scheuber, H. and Brinkhof, M.W.G. (2004) Juvenile immune system activation
induces a costly upregulation of adult immunity in field crickets Gryllus campestris.
Proceedings of the Royal Society of London, B- Biological Sciences, 272: 63-69.
Meyering-Vos, M. and Müller, A. (2007) RNA interference suggests sulfakinins as
satiety effectors in the cricket Gryllus bimaculatus. Journal of Insect Physiology, 53:
840-848.
Murray, A. and Cade, W. (1995) Differences in age structure among field cricket
populations (Orthoptera: Gryllidae): possible influence of a sex-biased parasitoid.
Canadian Journal of Zoology, 73: 1207-1213.
Walker, T.J. and Masaki, S. (1989) Natural History, In: Cricket Behavior and
Neurobiology (eds. Huber, F, Moore, T.E. and Loher, W), Cornell University Press,
Ithaca, NY. pp. 1-42.