Population dynamics and foraging behaviour ofDiaeretus leucopterus(Hymenoptera: Braconidae), and its potential for the biological control of pine damagingEulachnusspp. (Homoptera: Aphididae)

Abstract

The Palaearctic pine aphids, Eulachnus agilis (Kaltenbach) and Eulachnus rileyi (Williams) have both been introduced into other continents where they have been reported causing damage to economically important pines. In Euorpe, they are attacked by the specialist parasitoid Diaeretus leucopterus (Haliday) which has been suggested as a possible biological control agent. Here we report on several aspects of the ecology of the parasitoid, conducted on E. agilis in Germany in 1993–94, to provide a more scientific basis for judging its potential for use in biological control. Parasitism of all instars in the field rarely exceeded 10% and was independent of host density. A high percentage of parasitized aphids were hyperparasitized. Measurements of the impact over 16 weeks in a greenhouse-release experiment showed that parasitism rates increased from 2 to 19% but were insufficient to suppress the aphid population below a damaging level. There was evidence of a density-dependent response. Studies on foraging behaviour showed that female parasitoids searched pines by quite extensive walks. There was no relationship between the number of aphids per tree and number of ovipositions, and the mean number of ovipositions per female per tree was 2.5 ± 0.4 eggs. The majority (55.1%) of encountered aphids did not respond to the parasitoids. However, female parasitoids attacked a much higher proportion of aphids that did respond but oviposition success on this group was poor. The number of aphid-infested needles on seedlings increased significantly owing to the parasitoid's foraging activity. On the basis of these results, it is suggested that D. leucopterus is only likely to be of benefit in biological control if used in conjunction with other complementary natural enemies.

Weeds, aphids, and specialist parasitoids and predators benefit differently from organic and conventional cropping of winter cereals

“…The significant relationship between the abundances of grass aphids and of parasitoids could be addressed as a cascade-up mechanism that is mediated by density-dependent factors, since many of the parasitoid species identified in our study attack grass aphids, such as those of the Sitobion and Metopolophium genera (see Appendix 4 in Supplementary Material). The response between the grass aphids and parasitoids is in agreement with studies that have reported a density-dependent relationship between aphids and specialist aphidophagous parasitoids (Colfer and Rosenheim 2001;Helms et al 2004;Murphy and Volkl 1996). Nevertheless, in no case was the density-dependent parasitism by parasitoids sufficient to prevent an exponential population growth of the aphids within the growing season (Helms et al 2004).…”

Seasonal Abundance of the Oleander Aphid Aphis Nerii Boyer De Fonscolombe (Homoptera, Aphididae) in Relation to the Primary and Hyper-Parasitoids on Duranta in Egypt.

“…The mean total of parasitism was 7.34 % (Table 8). As in many aphid-parasitoid relationships (Walker et al, 1984;Murphy andVolkl, 1996, andStechmann, 1998), parasitoids did not play a significant role in regulating population growth of A. nerii on Asclepias species. Aphid densities continued exponential growth up to the end of the growing season (Sandra et al, 2004).…”

“…Results have been variable, leading to no general consensus. Parasitism of aphids has been shown to be density dependent (Walker et al, 1984;Murphy andVolkl, 1996 andColfer andRosenheim, 2001), inversely density dependent (Walker et al, 1984 andZhang andChen, 1993) and density independent (Zhang and Chen, 1993;Ferguson andStiling, 1996 andMurphy andVolkl, 1996), varying with the species and system under study. Kavallierators et al (2001) in Greece showed that the most common species of parasitoids attacking the oleander aphid A. nerii were the braconid wasps, Aphidius colemani Viereck, binodoxys angelicae Hal.…”

Within‐patch search flights by Pachyneuron aphidis (Hym., Pteromalidae): a potential strategy to compensate reduced foraging speed by foot

“…The performance of search flights might be essential for slowly moving parasitoids contrary to the intensive search‐by‐foot behaviour of quickly walking species. In pine systems the latter strategy is used by Diaeretus leucopterus (Haliday) (M URPHY and V ÖLKL , 1996), although the typical representative among aphid hyperparasitoids is D. carpenteri. A comparison of host contact rates/hour, although biased by the presence of ants in the examined system, indicates that, if foraging solely by foot, the quickly moving D. carpenteri females achieve more host contacts than P. aphidis , especially with increasing patch residence times (table 2, usual patch residence times of D. carpenteri see V ÖLKL et al., 1995).…”