Egg parasitoids of Thaumetopoea pityocampa (Den. & Schiff.) (Lep., Thaumetopoeidae) and their impact in SW Turkey

Abstract: Egg parasitoids (Hym., Chalcidoidea) and egg parasitism were studied in 132 egg batches of the pine processionary moth collected from stands of Pinus nigra Arnold and P. brutia Ten. in SW Turkey, at four places in heights of 800–1010 m a.s.l. in October 1998, beyond the caterpillars’ hatch. The egg batches deposited on P. nigra were high‐significantly smaller than those found on P. brutia. In this mountainous regions, Baryscapus servadeii (Dom.) and Ooencyrtus pityocampae (Mercet) were the most abundant egg parasitoids of Thaumetopoea pityocampa (Den. & Schiff.). Considering the different sampling places, Trichogramma sp. was found maximally in 3.1% of the parasitized eggs. Additionally, the hyper‐parasitoid Baryscapusransversalis Graham (mean infestation 1.8%) and Pediobius bruchicida (Rond.) (0.1%), both occurring in both sexes, and Anastatus bifasciatus (Fonsc.) (0.1%), only females, were established. The primary parasitoid O. pityocampae dominantly parasitized the eggs placed near the top of the batches, and B. servadeii was found mainly in eggs near the base. The rate of parasitism of the egg batches was very variable. The impact of egg parasitoids and predators varied from 24 to 35.9% depending on the sampling place. The hatching rate of the caterpillars was reduced to 50.7–65.6%. Under laboratory conditions, the emergence dynamics of the parasitoids showed a peak of B. tranversalis in December of the year, in which the host eggs were laid. Baryscapus servadeii emerged mainly in March–May of the following year, when the second part of O. pityocampae appeared. A large part of both parasitoids emerged before sampling of the batches. In O. pityocampae 1.65% and in B. servadeii 2.23% males developed under laboratory conditions. A rate of 15.7% of O. pityocampae and 7.9% of B. servadeii died in the eggs. The polyembryonic Trichogramma sp. (see also Tsankov et al., 1996a ) attacked 1.8% of the eggs. Up to 20 (mean 12) dead pupae were found in one egg. Minor parts of eggs were undeveloped (2.9%) and 0.6% totally empty.     

Intrinsic competition between primary hyperparasitoids of the solitary endoparasitoid Cotesia rubecula

1. In nature, competitive interactions occur when different species exploit similar niches. Parasitic wasps (parasitoids) often have narrow host ranges and need to cope with competitors that use the same host species for development of their offspring. When larvae of different parasitoid species develop in the same host, this leads to intrinsic and often contest competition. Thus far, most studies on intrinsic competition have focused on primary parasitoids. However, competition among primary hyperparasitoids, parasitic wasps that use primary parasitoids as a host, has been little studied. 2. This study investigated intrinsic competition between two primary hyperparasitoids, the gregarious Baryscapus galactopus and the solitary Mesochorus gemellus, which lay their eggs in primary parasitoid larvae of Cotesia rubecula, while those in turn are developing inside their herbivore host, Pieris rapae. The aims were to identify: (i) which hyperparasitoid is the superior competitor; and (ii) whether oviposition sequence affects the outcome of intrinsic competition. 3. The results show that B. galactopus won 70% of contests when the two hyperparasitoids parasitised the host at the same time, and 90% when B. galactopus oviposited first. When M. gemellus had a 48 h head start, the two hyperparasitoids had an equal chance to win the competition. This suggests that B. galactopus is an intrinsically superior competitor to M. gemellus. Moreover, the outcome of competition is affected by time lags in oviposition events. 4. In contrast to what has been reported for primary parasitoids, we found that a gregarious hyperparasitoid species had a competitive advantage over a solitary species.     

Testing for host‐associated differentiation in two egg parasitoids of a forest herbivore

Several studies underline the importance of ecological barriers and differential selection in driving sympatric speciation. Host‐associated differentiation (HAD) has been proposed as one of the mechanisms leading to sympatric speciation. However, it is still unclear how common HAD is or which are the factors that could promote it. In particular, not much is known about HAD in predators and parasitoids of herbivorous insects. One of the characteristics postulated to pre‐dispose insects to HAD is parthenogenesis as it may favour adaptive responses to particular environments, amplifying selected gene complexes. In this study, we used amplified fragment length polymorphism (AFLP) markers to determine whether HAD is present in two parthenogenetic egg parasitoids attacking the same herbivore species – the pine processionary moth, Thaumetopoea pityocampa (Denis & Schiffermüller) (Lepidoptera: Notodontidae) – on two host Pinus species. A total of 100 loci for 59 individuals sampled in four populations of Baryscapus servadeii (Domenichini) (Hymenoptera: Eulophidae), a specialist parasitoid, and 106 loci for 117 individuals sampled in six populations of Ooencyrtus pityocampae Mercet (Hymenoptera: Encyrtidae), a generalist parasitoid, were analysed. Levels of genetic differentiation were also assessed with an outlier analysis, checking for alleles associated to host plants. No evidence of HAD was detected in any of the two parasitoid species. We hypothesize that both the lack of strict parthenogenetic reproduction and the ectophagous nature of the insect host could explain the absence of HAD. The genetic variation observed in the generalist parasitoid responded to a pattern of local adaptation, whereas no relationship with either host or geography was found in the specialist parasitoid.     

Honeydew feeding increased the longevity of two egg parasitoids of the pine processionary moth

The longevity of a generalist (Ooencyrtus pityocampae) and a specialist (Baryscapus servadeii) egg parasitoid of the pine processionary moth (Thau‐metopoea pityocampa) was compared under laboratory feeding conditions including water and honeydew from aphid species growing on maritime pine (Pinus pinaster) or pedunculate oak (Quercus robur). The longevity of both parasitoid species increased when specimens were fed with honeydew. This increase was larger for the generalist (3.7, 32.0 and 38.0 days) than for the specialist (3.0, 23.3 and 21.5 days) parasitoid species when fed with water, oak and pine aphid honeydew respectively. The phenology of the specialist species B. servadeii is well‐adapted with its host availability with or without food supply. The generalist species O. pityocampae could overlap its host emergence curve during 14.0–20.0 days when fed with oak and pine aphid honeydew respectively, vs. no overlap when no supplementary food was provided. Analysis of honeydew composition indicated that sugars and amino acids may have distinct effects on parasitoid longevity.