Defensive behaviour against hyperparasitoids
Hyperparasitoids occur in 21 families of Hymenoptera and parasitize a
wide range of other parasitoids, which are also mostly hymenopterans
(Brodeur, 2000). Most hyperparasitoids attack parasitoids whose hosts
are other arthropods, but a few species parasitize conspecifics or other
species of hyperparasitoids. Thus, typical parasitoids that attack other
arthropods are sometimes called primary parasitoids, hyperparasitoids
that attack primary parasitoids are called secondary parasitoids and
hyperparasitoids that parasitize hyperparasitoids are called tertiary
parasitoids. There are even a few documented cases of quaternary para-
sitism (Gauld and Bolton, 1988). While hyperparasitoids are common to
many parasitoid guilds, surprisingly little is known about their biology,
with the possible exception of those that attack parasitoids of aphids. As
noted above, some aphid parasitoids reduce their risk of being located by
hyperparasitoids by altering the behaviour of their hosts. In contrast,
mature larvae of the hyperparasitoid Dendrocerus carpenteri (Mega-
spilidae) defend themselves from tertiary parasitism by possessing spine-
like projections on their body, which function as armour. These larvae
also thrash violently when approached by another hyperparasitoid adult
(Bennett and Sullivan, 1978; Carew and Sullivan, 1993).Competition among solitary and gregarious parasitoids
Parasitoids are solitary, with only one offspring surviving to adulthood
per host, or gregarious, with multiple offspring produced per host. Soli-
tary parasitoids sometimes lay more than one egg per host (Rosenheim
and Hongkham, 1996) and hosts attacked by solitary parasitoids can
also be superparasitized by a conspecific or multiparasitized by another
species. Oviposition of multiple egg clutches by some solitary parasitoids
can be favoured if they increase the probability that one offspring
will survive in the host (Rosenheim, 1993). For example, studies with
parasitoids ofDrosophilaand scale insects have found that laying of
multiple eggs reduces the host’s encapsulation response, which increases
the chance that at least one offspring will survive (Blumberg and
Luck, 1990; van Alphen and Visser, 1990). Although adult parasitoids are
usually able to distinguish parasitized from non-parasitized hosts, super-
or multiparasitism can be favoured if offspring have some chance
of surviving competition (van Alphen and Visser, 1990). The extent of
the disadvantage in attacking an already parasitized host depends on
the amount of time between ovipositions, with recently parasitized
hosts generally affording the greatest probability for survival (Strand and
Godfray, 1989; Visser, 1993).
For solitary species, hosts usually provide only enough host resources
for the development of one individual, which results in intense comp-
etition when more than one parasitoid is present. Solitary parasitoidsInteractions between Larval Parasitoids and Their Hosts 141