Eleven species of parasitoids were found to attack 7 species of wheat aphids in Iran. The Simpson's Index of diversity (D) used to compare the aphidiine diversity in various cereal crop systems in geographically different regions of Iran ranged from 0.197 to 0.488, depending on locality. There were significant differences among species diversities at different altitudes. The central highlands (1000-1500 meters above mean sea level) were the areas with the most diverse aphid parasitoid complex, differing significantly from that at lower and higher altitudes. We found that altitude explained about 10% of the cereal aphid parasitoid distribution pattern in Iran. Species of the genus Aphidius Nees were the most abundant and widely distributed. These were Aphidius rhopalosiphi De Stefani, Aphidius uzbekistanicus Luzhetski, Aphidius colemani Viereck and Aphidius matricariae Haliday. A. uzbekistanicus, Ephedrus plagiator (Nees) and Ephedrus persicae Froggat were encountered mainly on the plains at lower altitudes. Diuraphis noxia (Kurdjumov) was mainly recorded at higher altitudes in Iran along with its dominant parasitoid species, Diaeretiella rapae (MIntosh). The fact that Iran is close to the presumed area of D. noxia origin (Central Asian submountains) could be very important in further biological control efforts against this pest aphid. According to our results, Aphidius ervi Haliday is a very rare parasitoid of cereal aphids in Iran, which contrast with its high abundance in Europe and North America.
Aphis fabae and Myzus persicae (Hemiptera: Aphididae) are insect pests that damage sugar beet and bean crops. Both are responsible for losses in yield and transmission of viral diseases, and may be present on the same host at the same time. Three parasitoid species, Aphidius colemani, Lysiphlebus testaceipes and Lysiphlebus fabarum (Hymenoptera: Braconidae: Aphidiinae) have the potential to be used as biological control agents against at least one of these species of aphids. As a first step prior to the implementation of a biological control program, our aim was to understand the host selection behaviour of the parasitoids, particularly when both aphids are present. We recorded the host acceptance (number of insertions of the ovipositor / number of antennal contacts), suitability (number of mummies / the number of insertions of the ovipositor) and emergence (number of adults emerging from mummies) of these three aphid parasitoids when parasitizing the two aphids. We also analyzed the effect of the host plant on the host preference of the parasitoid. Females of each parasitoid species (n = 15) were exposed to 20 aphids of A. fabae or M. persicae, or a mixture of these two species of aphids, for 15 min, on a leaf disc of each of the two host plants, sugar beet and bean. Higher host acceptance and suitability were recorded for A. colemani attacking both species of aphid: A. fabae (43 and 46%) and M. persicae (43 and 46%) on beet and bean plants respectively, compared to L. testaceipes and L. fabarum. L. testaceipes and L. fabarum showed a clear preference for A. fabae. L. fabarum accepted M. persicae on both plants only when it was mixed with A. fabae, probably due to a confusion effect. We found that the host plant played a significant role in host acceptance, host suitability. We conclude that A. colemani is the better of the three parasitoids studied for the biological control in bean, and particularly, sugar beet crops. and Loulou Albittar, Mohannad Ismail, Claude Bragard, Thierry Hance.
Monoctonus paulensis is a solitary parasitoid of several species of aphids, including the pea aphid, Acyrthosiphon pisum. We evaluated host-instar selection by comparing the parasitoid's preference for the four nymphal instars of the pea aphid, presented two at a time in dichotomous choice tests. Females parasitized more, and laid more eggs in, the relatively smaller aphids among those available. This preference was independent of aphid instar: L1 > L2 > L3 > L4. Preference was not influenced by female size or age. Normal and anaesthetized aphids were accepted equally. The total time needed by a female to capture, position, and parasitize an aphid varied among host instars, with fourth instars requiring nearly twice as much time as first, second, and third instars. The probability of an attacked aphid escaping or avoiding parasitism increased with aphid instar, from ~10% in first and second instars to ~50% in fourth instars. Although fourth-instar pea aphids contain more resources for offspring development than smaller counterparts, it may not be profitable for a female to invest opportunity time in attacks on large aphids.
In the mating behaviour of Aphidius ervi Haliday the antennae play a pivotal role in partner recognition and acceptance. Mating failure was always observed when antennal contact was experimentally prevented. The male of A. ervi has filiform antennae, consisting of scape, pedicel and 18-20 cylindrical antennomeres (flagellar segments), which bear numerous types of sensory structures and, interspersed among the multiporous plate sensilla, especially on the 1th and 2nd flagellar segments, scattered pores. A secretion oozes from these pores in virgin males exposed to conspecific females. Transmission electron microscopy revealed that these pores are the external openings of integumentary glands. Behavioural and morpho-functional observations indicated that a double step sex recognition mechanism is present in A. ervi, as in other parasitic Hymenoptera. Basically, female recognition by males appears to be mediated by a volatile sex pheromone, that triggers the behavioural sequence leading to mounting. Then, the female recognizes and accepts the male after antennal contact. This is mediated by the secretion that oozes from the male antennal glands, which acts as a contact pheromone.
Phylogenetic relationships among 16 genera of the subfamily Aphidiinae (Hymenoptera: Braconidae) were investigated using sequence data from three genes: the mitochondrial large ribosomal subunit (16S), 18S ribosomal DNA and mitochondrial ATPase 6. All sequences were downloaded from the GenBank database. A total of 2775 base pairs of aligned sequence were obtained per species from these three genes. The results support the existence of three-tribes: Ephedrini, Praini and Aphidiini, with the Ephedrini occupying the basal position; Aphidiini could be further subdivided into three subtribes: Monoctonina, Trioxina and Aphidiina. The genus Aphidius is a paraphyletic group. The taxonomic status of the subfamily Aphidiinae within the Braconidae is probably closer to the non-cyclostome than the cyclostome subfamilies.
Body size is a standard criterion of quality control in insect rearing and often assumed to correlate with fitness in parasitoid wasps, but various metrics of body size can be used. The purpose of this study was to determine which morphological feature provides the best correlation with body size and egg load in a thelytokous population of the parasitoid wasp, Lysiphlebus fabarum (Marshall), when reared on Aphis fabae Scopoli under standardized conditions in a growth chamber (21 ± 1°C, 60–70% RH, and 16L : 8D). Candidate metrics included head width, length and width of the pronotum, length and width of the right forewing, and length of the right hind tibia. In the first experiment, correlations were determined between these measurements and overall wasp body length. As head width and hind tibia length emerged as the most suitable proxies for total body length, the next experiment these two variables as proxies for egg load in females reared from different nymphal instars of the host aphid. There was a non-linear relationship between body size and egg load of wasps emerging from hosts parasitized in different nymphal instars. Egg load increased linearly with body size across all host growth stages, but the second nymphal instar was the most suitable stage for parasitism when speed of development was factored in. The results suggest that head width is a suitable morphometric for monitoring quality control in mass-reared cultures of this wasp., Mohammad Ameri ... [et al.]., and Obsahuje seznam literatury
Field studies were conducted, in order to assess the seasonal occurrence and the spatial distribution of Aphidius colemani Viereck, Aphidius matricariae Haliday, Diaeretiella rapae (M'Intosh), Praon staryi Kavallieratos & Lykouressis and Praon volucre (Haliday), all parasitoids of Myzus persicae (Sulzer) on tobacco. The experiments took place in western Greece (Agrinion, Aitoloakarnania), during the 1996 and 1997 growing seasons, in an area of approximately 2.5 ha, where tobacco was the main crop. The experimental field was insecticide-free and tobacco leaf samples (from the upper and lower half of plants) were taken from June until September, in both years. The distribution of the species found was also represented and discussed. Generally, high M. persicae densities were recorded in August (mid-season) of both seasons. The mummification rate showed a specific increasing trend late in the season (August-September). In 1996, the percentage of mummification reached almost 61% at the end of the period, whereas in 1997 it remained at very low levels (<2%). The density of M. persicae was higher on the leaves collected from the upper part of the plants than on those from the lower part, but without significant difference. In contrast, the numbers of mummified M. persicae individuals were significantly higher on leaves collected from the lower part of the plants than on those from the upper part in both years. The relative abundance of the aphidiine parasitoid species differed between the two years.
We examined the influence of offspring mortality caused by hyperparasitism on the secondary sex ratio of Lysiphlebus hirticornis Mackauer, a solitary endoparasitoid of the aphid Metopeurum fuscoviride Stroyan, in the field. Females of L. hirticornis produce pseudo-gregarious broods, which may comprise more than 200 offspring. Hyperparasitoids [mainly Syrphophagus aphidivorus (Mayr)] attacked and killed up to 60% of the primary parasitoids inside mummified aphids, especially late in the season. Hyperparasitized broods were larger than hyperparasitoid-free broods, which suggests that the risk of hyperparasitism increased with mummy density. We tested the hypothesis that mortality caused by hyperparasitism is greater for female than male offspring of L. hirticornis. If mummy quality scales with mummy size, hyperparasitoids should choose the relatively larger over the relatively smaller mummies. In the absence of hyperparasitism, broods of L. hirticornis included approximately two daughters for each son; the sex ratio did not vary with brood size. In hyperparasitized broods, the sex ratio was nearly even. This result indicates that relatively more female offspring (developing in the larger mummies) than male offspring (developing in the smaller mummies) were killed by hyperparasitoids. We propose that sex-differential offspring mortality in L. hirticornis is the result of differences in optimal host choice between the primary parasitoid and the hyperparasitoids.
The taxonomic status of the aphid parasitoid Aphidius colemani Viereck has been questioned, especially in regard to Aphidius transcaspicus Telenga (Hymenoptera: Braconidae). The genetic association between A. colemani and A. transcaspicus was studied by cross mating individuals of A. colemani and A. transcaspicus (A.c.& × A.t.% and A.c.% × A.t.&) and applying appropriate molecular methods. The cross mating resulted in offspring (female and males) that were fertile. Therefore, the cross mating assays performed in an artificial environment showed that these two populations are potentially compatible. The mean number of mummies that developed and the sex ratio of the offspring of each cross were similar. Most of the male and female offspring from each cross were assigned to A. transcaspicus. Furthermore, the genetic divergence between the ribosomal internal transcribed spacers (ITS2) of the A. colemani and A. transcaspicus studied was 16%. These results indicate that A. colemani might be a complex of species with different morphological and biological characters attacking different host aphids.
A suitable host provides, at least, the minimum nutritional and physiological conditions for the development of the immature stages of a parasitoid. Host quality may influence the developmental time, mortality rate, longevity and fecundity of parasitoids. This work evaluates the suitability and quality of Aphis gossypii Glover, Brevicoryne brassicae (Linné), Myzus persicae (Sulzer), Rhopalosiphum maidis (Fitch) and Schizaphis graminum (Rondani) as hosts for Aphidius colemani Viereck. Twenty second-instar nymphs of each aphid species were exposed to parasitism for one hour, and then kept in a climatic chamber at 22 ± 1°C, 70 ± 10% RH and a 12 h photophase. The aphid B. brassicae was unsuitable for the development of A. colemani. The different aphid host species varied in size: M. persicae > (R. maidis = S. graminum) > A. gossypii. Parasitoid fitness decreased accordingly when reared on (M. persicae = R. maidis) > S. graminum > A. gossypii. Large hosts seem to be better than small hosts based on parasitoid size. Egg load of A. colemani was related probably more on the ability of the parasitoid larva to obtain nutritional resources from the different host species than on host size.