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very high levels of host specificity, having much narrower diets that ectohy-
perparasitoids ( Sullivan and Volkl, 1999 ).
B. Developmental Diapause
Hosts that have been attacked by koinobionts ( Table 1 ) will continue develop-
ment while the parasitoid offspring develops inside them. The parasitoid off-
spring inside the host will generally undergo embryonic diapause, allowing the
host to reach a suitable size, and hence provide a suitable level of nutrition,
before entering the larval stage ( Godfray, 1994 ). Because the host is not
paralysed by the act of oviposition, it is thought that, in order to protect the
egg from the machinations of the host, many koinobionts are also endopar-
asitoids ( Pennacchio and Strand, 2006 ). As such, in order to evolve successful
countermeasures against host internal defences, they suffer the constraints to
diet breadth associated with endoparasitism outlined above. Idiobionts
( Table 1 ) typically paralyse their hosts during oviposition and their larvae do
not have to contend with host defences, and idiobionts generally exhibit an
ectoparasitoid life history ( Hawkins, 1994 ). This generalisation is not universal
but, rather, the rule with some exceptions. Parasitoid wasps of the genus group
Polysphicta, for example, are koinobiont ectoparasitoids that place their eggs in
such a manner as to avoid disposition by the host ( Gauld and Dubois, 2006 ).
A more detailed review of the relationship between koino/idiobiosis and diet
breadth, with empirical evidence, can be found in Hawkins (1994) .
According to the 'Dichotomy hypothesis', the long development time
associated with koinobiontism further constrains parasitoid fundamental
niche in regard with the developmental stage of the host that they can attack.
Koinobionts must attack earlier developmental stage hosts in order to have
the time required to complete development ( Blackburn, 1991; Godfray, 1994;
Hawkins, 1994 ). Conversely, because their hosts represent all of the available
nutrition for their offspring, idiobionts must attack larger late stage hosts to
ensure that offspring have the energy available to complete development.
This concept is one of the fundamental theories in parasitoid ecology, and the
developmental stage of the host used has been hypothesised to be an impor-
tant driver of life history and morphology ( Godfray, 1994 ); this concept will
be revisited when we discuss realised niches in parasitoids.
Hyperparasitoids are also either koinobionts or idiobionts. Idiobiont
hyperparasitoids are constrained in that they have to attack their hosts
during the mummy stage; koinobionts typically attack while the primary
parasitoid's host is still alive or rarely during the mummy stage. Very few
koinobiont hyperparasitoids can utilise both host stages ( Buitenhuis et al.,
2004 ). These host stage constraints have, for example, been shown to play an
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