Pea aphid clonal resistance to the endophagous parasitoid Aphidius ervi.

The physiological mechanism of resistance to the endophagous braconid Aphidius ervi Haliday (Hymenoptera, Braconidae) by a pink clone (PC) of Acyrthosiphon pisum (Harris) (Homoptera, Aphididae) has been investigated. Comparative data on parasitoid development and associated host biochemical changes in the resistant PC aphids and in a susceptible green clone (GC) of A. pisum are reported. When the PC aphids were attacked as early 4th instars, the developing parasitoid larvae showed a strongly reduced increase in size, compared to those synchronously developing in GC aphids, and were unable to produce a regular mummy. In contrast, parasitism of 2nd instar PC aphids, allowed completion of parasitoid development, but adults had a prolonged developmental time, due to a longer duration of parasitoid's final (3rd) instar. In all cases, teratocytes, cells deriving from the A. ervi serosal membrane, and the proteins abundantly synthesised by them, were never found in the haemolymph of parasitised PC aphids. Host castration, as demonstrated by total protein incorporation into reproductive tissues, was total in the majority of early (2nd instar) parasitised host aphids, while it was limited when later instars (4th) of PC aphids were parasitised. This is partly due to the absence of the cytolytic activity of teratocytes on host embryos, which, through their persistence, may compete for nutritional resources with the developing parasitoid larvae. In parasitised PC aphids, this competitive effect is further aggravated for the parasitoid by the absence of the regulated amino acid titre increase in the host haemolymph, which is regularly observed in GC aphids. Failure of teratocyte development in the PC clone of the pea aphid is, then, the major functional constraint accounting for the reduction/inhibition of A. ervi larval growth. The reported results allow to assess in vivo the role of teratocytes in the host physiological redirection and nutritional exploitation by the parasitoid, and to integrate and validate the proposed physiological model of host-parasitoid interactions in the system A. pisum-A.ervi.

A comparative study on hypertrehalosaemic hormones in the Hymenoptera: sequence determination, physiological actions and biological significance.

A new hypertrehalosaemic peptide (Tea-HrTH; pQLNFSTGWGG-NH(2)) was isolated from the corpora cardiaca (CC) of the sawfly Tenthredo arcuata. The hypertrehalosaemic peptides found in the CC of five Bombus species and the paper wasp Polistes fuscata were identical to the adipokinetic hormone II of the desert locust, Schistocerca gregaria (Scg-AKH-II). The hypertrehalosaemic peptides found in the yellowjacket Vespula vulgaris and the hornet Vespa crabro were identical to the adipokinetic hormone of the cricket, Gryllus bimaculatus (Grb-AKH).All species examined had a large storage crop which, when filled with honey, held up to one-third of their total body weight. Overwintering queens of P. fuscata had large stores of carbohydrates and lipids in the abdomen, and were able to survive months of fasting. Workers of Bombus hortorum (bumble-bee), Apis mellifera (honey-bee) and V. vulgaris had little or no fat body. These species could fly as long as sugar was present in their crops, but they stopped flying as the carbohydrates in the crop disappeared. There was no significant increase in the haemolymph carbohydrate titres after injections of CC extracts or corresponding synthetic peptides into workers of B. hortorum or into males and females of T. arcuata. There was a moderate increase in haemolymph carbohydrate titres when these peptides were injected into overwintering queens of P. fuscata and into workers of V. crabro, both with significant amounts of fat body. However, well-fed V. vulgaris workers, with very little fat body, also responded to their own hypertrehalosaemic peptide.

A phylogeny of aphid parasitoids (Hymenoptera: Braconidae: Aphidiinae) inferred from mitochondrial NADH 1 dehydrogenase gene sequence.

Wasps of the braconid subfamily Aphidiinae are solitary endoparasitoids of aphids. Several aspects of their biology have been the focus of intuitive evolutionary hypotheses which could be tested with a robust phylogeny. Phylogenetic hypotheses have been proposed previously for aphidiines based on morphology, embryology, and DNA sequences. However, many of them are based on a limited number of characters and/or taxa and lack congruence. In addition, many of the inferred phylogenies have not been based upon cladistic analysis. Therefore, a phylogenetic study of Aphidiinae was undertaken, utilizing 465 bp of DNA sequence of the mitochondrial NADH1 dehydrogenase gene. DNA sequences were obtained from 40 taxa, including 14 genera and three outgroups. It is suggested that in agreement with most of the previously proposed phylogenies, the aphidiines, each of the three recognized tribes (Praini, Ephedrini, Aphidiini), and most genera are monophyletic. In contrast to previously proposed phylogenies, the clade of Praon + Dyscritulus (=Praini), rather than Ephedrini, is basal among the aphidiines.

Invasion of one insect species, Adalia bipunctata, by two different male-killing bacteria.

Male-killing bacteria, which are inherited through the female line and kill male progeny only, are known from five different orders of insect. Our knowledge of the incidence of these elements has stemmed from discovery of their phenotype in different species. Our estimate of the frequency with which insects have been invaded by these elements therefore depends on each observation of the male-killing phenotype within a species being associated with a single microorganism. We here record an example of a single insect species being infected with two taxonomically distinct male-killing bacteria. Western European populations of the two-spot ladybird, Adalia bipunctata, have previously been shown to bear a male-killing Rickettsia. However, we here show that the majority of the male-killing lines tested from Central and Eastern Europe do not bear this bacterium. Rather, 16S rDNA sequence analysis suggests male-killing is associated with a member of the genus Spiroplasma. We discuss this conclusion in relation to the evolutionary genetics of male-killing bacteria, and the evolution of male-killing behaviour in the eubacteria.

Hyperparasitism: multitrophic ecology and behavior.

Hyperparasitoids are secondary insect parasitoids that develop at the expense of a primary parasitoid, thereby representing a highly evolved fourth trophic level. This review evaluates multitrophic relationships and hyperparasitoid ecology. First, hyperparasitoid communities of various taxa of phytophagous and predacious insects are described. Second, specific patterns of hyperparasitoid community organization and hyperparasitoid ecology are described in detail, using the aphid-parasitoid-hyperparasitoid food web as a model system. Aphid hyperparasitoid communities consist of ecto- and endohyperparasitoids, with ectohyperparasitoids being less host specific than endohyperparasitoids. Lifetime fecundity and intrinsic rate of increase of hyperparasitoids are generally lower than those of their primary hosts. Aphid ectohyperparasitoids search randomly for hosts and do not use specific cues, whereas endohyperparasitoids gain information that originates from host plants or hosts for long-range search. Interactions with adult primary parasitoids do not influence hyperparasitoid searches, but aphid-attending ants typically prevent successful hyperparasitoid foraging. Impact of hyperparasitism on biological control is reviewed.

Comparison of ecdysteroid concentration in different morphs of aphids.

The amounts of ecdysteroids were determined in different morphs of holocyclic monoecious aphids (Acyrthosiphon pisum Harris, Dysaphis devecta Walk., Lachnus roboris L., Schizolachnus pineti F.) and holocyclic heteroecious aphids (Aphis sambuci L., Rhopalosiphum padi L.) by means enzyme immunoassay. Among the parthenogenetic morphs (fundatrices, virginoparae, and oviparae), the fundatrices have consistently higher amounts of ecdysteroids than those of other morphs of the same species. Alate and apterous virginoparae showed slight differences in their ecdysteroid titer both in heteroecious and monoecious aphids. The migrant morphs (i.e., alate fundatrices and gynoparae) have the lowest amounts of ecdysteroids within a species. With the exception of D. devecta, the oviparae of both heteroecious and monoecious aphids have the second greatest amounts of ecdysteroids among the morphs living on same host plant. Polyphenism, dispersal behavior, and fecundity in connection with weight, ovariole number, and ecdysteroid concentration of different morphs of aphids are discussed.

Interactions betweenAlloxysta brevis (Hymenoptera, Cynipoidea, Alloxystidae) and honeydew-collecting ants: How an aphid hyperparasitoid overcomes ant aggression by chemical defense.

Foraging females of the aphid hyperparasitoidAlloxysta brevis were attacked by honeydew-collecting workers of the antLasius niger at the first encounter. However, ants abandoned their attacks quickly, and foragingA. brevis remained unmolested for a subsequent time interval of approximately 5 min, which is long enough for the hyperparasitoid to oviposit successfully. Furthermore, freshly killed intactA. brevis were disregarded by ants, while decapitated specimens were readily removed. We present evidence thatA. brevis females release a mandibular gland secretion, which contains 6-methyl-5-hepten-2-one, actinidin, and unidentified iridoids, in response to an ant attack. This secretion functions both as a measure of self-defense if the female is seized by an ant worker and as a repellent, which prevents ant attacks during subsequent encounters. This is the first evidence for chemical defense in a hymenopterous parasitoid. It enablesA. brevis females to hyperparasitize ant-attended aphids that constitute a major proportion of their hosts and significantly reduces mortality by ectohyperparasitoids.

Regulation of aphid populations by aphidiid wasps: does parasitoid foraging behaviour or hyperparasitism limit impact?

Aphidiid parasitoids (Hymenoptera: Aphidiidae) of aphids generally exploit only a small percentage of the available host resources in the field. This limited impact on aphid populations has often been explained as a consequence of hyperparasitism. We propose that a wasp's reproductive strategy, as opposed to hyperparasitism, is the dominant factor in aphidiid population dynamics. A wasp's foraging efficiency and oviposition decisions are influenced by several variables, including searching behaviour between and within patches, host choice (as modified by the aphids' defensive behaviours), and plant structural complexity. Two broadly different patterns of host exploitation have evolved in aphidiid wasps in relation to ant-aphid mutualism. Firstly, in species that are exposed to predation and hyperparasitism, a female may leave a patch before all suitable hosts are parasitized. Because predators and hyperparasitoids tend to aggregate at high aphid or aphidiid densities, or in response to aphid honeydew, this strategy enables females to reduce offspring mortality by "spreading the risk" over several host patches. Secondly, in species that have evolved mechanisms to avoid aggression by mutualistic ants, females are able to exploit a hyperparasitoid-free resource space. Such species may concentrate their eggs in only a few aphid colonies, which are thus heavily exploited. Although hyperparasitism of species in the first group tends to reach high levels, its overall impact on aphid-aphidiid population dynamics is probably limited by the low average fecundity of most hyperparasitoids. We discuss the foraging patterns of aphidiid wasps in relation to aphid population regulation in general, and to classical biological control in particular. We argue that a parasitoid's potential to regulate the host population is largely determined by its foraging strategy. In an exotic parasitoid, a behavioural syndrome that has evolved and presumably is adaptive in a more diverse (native) environment may, in a more uniform (managed) environment, result in suboptimal patch-leaving and oviposition decisions, and possibly increased resource usage.

[Coenzym properties of some Ade-1- and Ade-N6-substituted NAD derivatives (author's transl)]. / Coenzym-Eigenschaften einiger in 1- und N6-Stellung des Adeninringes substituierter NAD-Derivate

By reaction of NAD with different oxiranes or with aziridine, derivatives of the coenzyme are obtained with substituents in position 1 or on the amino group in position 6 of the adenine ring. While the Ade-1-substituted derivatives show high Km values with different dehydrogenases and are reduced only very slowly by these enzymes, the coenzyme derivatives substituted at the amino group behave very similarly to NAD. Correlations were found between coenzyme efficiency of the compounds and the lipophilic character of their substituents. The results can be interpreted from the structure of the active site of the dehydrogenases investigated.