Interspecific competition between the principal larval parasitoids of the pine sawfly, Neodiprion sertifer (Geoff.) (Hym.: Diprionidae)

Abstract

Interspecific competition between the 3 principal larval parasitoids of the pine sawfly, Neodiprion sertifer, is of common occurrence when total larval parasitism, and hence multiple attack rates, are high. At the intrinsic level, the ectoparasitoid Exenterus abruptorius is superior to the 2 endoparasitoids, Lophyroplectus luteator and Lamachus eques, respectively, whereas L. luteator is superior to L. eques only. During mass outbreaks of the host competition between Exenterus and Lophyroplectus is most intense, whilst Lamachus fails to build up in the presence of its 2 competitors (Fig. 1). However, due to its superior host finding ability, Lamachus dominates in areas of low host densities where the 2 other species are less efficient (Table 1). L. luteator frequently sustains heavy losses in direct competition with E. abruptorius, but these can be largely compensated in the next generation because its fertility is about 5-times higher than that of Exenterus.

Mixed forests to mitigate risk of insect outbreaks

“…Between the end of June and the beginning of July, the larvae go through their final ecdysis and become pre-pupae that will leave the tree and find a place in the litter or soil to pass through the summer diapause and undergo pupation, which happens in the beginning of August. There is accumulated information on specialist parasitoids (Pschorn-Walcher 1965, 1967Griffiths 1975;Pschorn-Walcher 1987), predation by ants (Olofsson 1992), cocoon predation by small mammals (Hanski and Parviainen 1985;Hanski 1987;Olofsson 1987;Kouki et al 1998), the impact and transmission of nuclear polyhedrosis virus (NPV) during outbreaks (Olofsson 1989a(Olofsson , 1989b and mortality factors in general (Olofsson 1987). The species is distributed over North America and Eurasia and exhibits periodical outbreaks over its entire range.…”

Extrinsic Inter- and Intraspecific Competition in Parasitoid Wasps

“…When intrinsic competition favors the first parasitoid that attacks a host (81,195), species with slow search times have reduced foraging efficiency and risk being displaced by faster competitors (78). Extrinsic competition can counter the effects of intrinsic competition (33,38,63,141). An interesting example of this comes from a study of competitive displacement of a native parasitoid, Praon pequodorum (Braconidae), by Aphidius ervi, another braconid parasitoid introduced to P. pequodorum's home range to control the pea aphid.…”

Impacts of natural enemies and stand characteristics on cocoon mortality of the pine sawfly <i>Diprion pini</i> in a Fennoscandian boreal forest

“…The different outbreak stage may explain the variation in these results. Parasitoid populations can grow and reach their peak population density in the case of an extended outbreak period (Berryman 1986;Pschorn-Walcher 1987). The rate of cocoon parasitism appears to depend on the parasitoid complex and its ability to synchronize population dynamics with the host, along with environmental factors such as stand characteristics (Kidd and Jervis 1997;Turchin et al 2003).…”

“…Altering climatic conditions can also influence these interactions (Netherer and Schopf 2010). Response of the natural enemy complex is usually delayed compared to the phase in population density of the host organism (Berryman 1986;Pschorn-Walcher 1987).…”