Life history of the tick parasitoid Ixodiphagus hookeri (Hymenoptera: Encyrtidae) in Kenya

We conducted laboratory and field experiments to elucidate the life history of Ixodiphagus hookeri, a parasitoid of the ixodid tick Amblyomma variegatum in Western Kenya. Ixodiphagus hookeri females oviposited in unfed host nymphs as well as engorged nymphs, but rarely in engorged larvae. While I. hookeri developed to adults in engorged nymphs, the eggs laid in unfed nymphs disappeared within 2 days after oviposition. As temperature increased, development time of I. hookeri from oviposition to adult emergence in engorged nymphs decreased from 46 days at 23 °C to 35 days at 28 °C, and their immature survival in engorged nymphs decreased from 67% at 23 °C to 22% at 28 °C. No parasitoid adult emerged from hosts at 30 °C. Individual hosts parasitized by single females produced 42–53 adult wasps, 73% of which were females. As a typical pro-ovigenic species, I. hookeri females had an average of 84 mature eggs at emergence and lived only for a few days. When laboratory-reared, unfed nymphs of A. variegatum were attached to cattle for 4–9 days in subsistence farmers’ fields in Western Kenya, 25% of the engorged nymphs and 4% of the unfed nymphs on cattle were parasitized by I. hookeri, demonstrating that I. hookeri females search for and oviposit in A. variegatum nymphs on cattle. Unlike other strains of I. hookeri that overwinter as eggs in unfed nymphs, I. hookeri could continuously reproduce throughout the year in Western Kenya.     

Egg-laying experience and acceptance of parasitized hosts by the parasitoid,Leptopilina heterotoma (Hymenoptera: Eucoilidae)

The influence of egg-laying experience on the response of females of the eucoilid parasitoid,Leptopilina heterotoma, to parasitized and unparasitizedDrosophila melanogaster host larvae was examined under more controlled conditions than those used in past studies. In laboratory assays, we precisely manipulated both the number of eggs laid by females and the kind of larvae (parasitized versus unparasitized) in which the eggs were laid. We found that the tendency to avoid laying eggs in parasitized hosts depended markedly on whether or not eggs had been laid previously, but depended little on whether those eggs had been laid in parasitized or unparasitized hosts. The observed effect of general egg-laying experience on avoidance of parasitized hosts may reflect responses to either changes in the wasp's internal state (perhaps, changes in egg load) or changes in the wasp's neural representation of the external environment (such as those presumed to occur during learning). In light of these results, we offer a tentative reinterpretation of several earlier studies.     

Influences of plant species on life history traits of Cotesia rubecula (Hymenoptera: Braconidae) and its host Pieris rapae (Lepidotera: Pieridae)

The relative suitability of four plants was studied for larvae of Pieris rapae L. and its parasitoid Cotesia rubecula (Marshall). For unparasitized P. rapae, pupal dry weight and egg-pupa growth rate were higher on cabbage, radish and nasturtium than on Indian hedge mustard. Larval developmental rate and size were greatest for C. rubecula when its host was feeding on nasturtium. Wasp survival was not affected by the host insect/plant combination in which the parasitoid developed. These results indicate that the plant on which host larvae feed is an important factor in development of the parasitoid.     

Two tachinid species discriminate between parasitized and non-parasitized hosts

The abilities ofMyiopharus doryphorae (Riley) andM. aberrans (Townsend) (Diptera: Tachinidae) to discriminate between parasitized and non-parasitized Colorado potato beetle (host)Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae) larvae, were investigated under laboratory and field conditions. Laboratory experiments showed that bothMyiopharus species have a significantly greater frequency for larvipositing in non-parasitized hosts over parasitized ones. Direct field observations of larvipositional behavior of bothMyiopharus species over three growing seasons showed effective restraint from larviposition into parasitized hosts, while larviposition into nonparasitized ones occurred readily. Avoidance of previously-parasitized hosts occurred after the larvipositing flies briefly landed on host larvae without attempting to insert the larvipositor. The low levels of superparasitism which occurred in the caged experiments and in the field appeared to be due to a breakdown of the larvipositing parasitoids' restraint when they met only parasitized hosts or when many parasitoids competed for reduced numbers of hosts late in the season.     

Host discrimination in the parasitoid Ooencyrtus nezarae: the role of the egg stalk as an external marker

Laboratory experiments were conducted to examine the role of the egg stalk in host discrimination by Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae), an egg parasitoid of the bean bug, Riptortus clavatus Thunberg (Hemiptera: Alydidae). These experiments showed that females that have oviposited in unparasitized hosts within 1 h before the test discriminated between parasitized and unparasitized hosts. When protruding parts of the parasitoid's egg stalks were removed from hosts, the latter were accepted by experienced females. This suggests that the protruding portion of the parasitoid egg stalk functions as an external marker. This part of the egg stalk was responsible for host discrimination up to 8 days after parasitism. Internal discrimination was also observed on hosts 3 or 8 days after parasitism.

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Résumé Des expériences de laboratoire ont permis d'examiner l'influence du pédoncule de l'oeuf dans la sélection des hôtes par O. nezarae Ishii (Hym.: Encyrtidae), parasite d'oeufs de Riptortus clavatus Thunberg (Hemip.: Alydidae). Les femelles qui avaient pondu dans un hôte vierge dans l'heure qui avait précédé l'expérience ont été capables de choisir entre des hôtes parasités ou non. Quand la partie saillante du pédoncule de l'oeuf de parasitoïde avait été extraite de l'hôte, ce dernier avait été accepté par les femelles. Ceci laisse supposer que la partie saillante du pédoncule de l'oeuf fonctionne comme marqueur externe. Cette partie du pédoncule de l'oeuf a été responsable de la discrimination des hôtes jusqu'à 8 jours après qu'ils aient été parasités, montrant une plus longue efficacité comme marqueur externe que les phéromones externes observées chez d'autres parasitoïdes.

     

Visual Evaluation and Recognition of Hosts by the Tick Parasitoid, Ixodiphagus hookeri (Hymenoptera: Encyrtidae)

The role of host size, movement, feeding status, color, and species in the visual host evaluation and recognition behavior of the tick parasitoid, Ixodiphagus hookeri Howard was investigated. Freshly emerged female parasitoids were subjected to a choice bioassay, where the test materials were placed in sealed vials and the vials placed in a Petri dish. When presented with A. variegatum live and mummified nymphs, females examined: larger nymphs significantly longer than smaller nymphs, fed nymphs significantly longer than unfed nymphs, dead and live nymphs for similar lengths of time, and grey live nymphs and yellow-brown and dark brown mummified nymphs for similar lengths of time. The total number of visits to vials containing these test materials were also not significantly different, except there were significantly more visits to yellow-brown mummies when compared to the number of visits to dark brown mummies. When presented with A. variegatum (host) and R. appendiculatus (nonhost) nymphs, the females examined A. variegatum nymphs significantly longer than R. appendiculatus nymphs. The total number of visits to vials containing A. variegatum nymphs were significantly more than the visits to the vials containing R. appendicualtus nymphs. Furthermore, females spent significantly more total examination time per visit on larger and fed A. variegatum nymphs when compared to smaller and unfed nymphs, respectively. Direct and indirect detection were significant when females were presented with fed versus unfed A. variegatum nymphs, grey nymphs versus yellow-brown mummies, and R. appendiculatus versus A. variegatum nymphs. Direct and indirect detection for the rest of the bioassays were not significantly different. Finally, The percentages of females contacting large fed A. variegatum nymphs first were significantly different from those of females contacting small unfed R. appendiculatus nymphs first. The firstcontact percentages for the rest of the bioassays were not significantly different.     

Foraging Behaviour and Patch Exploitation by Campoplex dubitator (Hymenoptera: Ichneumonidae), a Parasitoid of Bark-mining Larvae

This study examines the foraging behaviour of Campoplex dubitator Horstmann (Hymenoptera: Ichneumonidae), a parasitoid of the highly concealed bark-mining host, Enarmonia formosana Scopoli (Lepidoptera: Tortricidae), and how this foraging behaviour is affected by host density. The ultimate aim was to determine whether foraging behaviour and patch fidelity could explain patterns of parasitism in the field. An ethogram was first constructed to portray C. dubitator behaviour prior to and immediately following host attacks. The pre-attack behavioural sequence was highly structured whereas behavioural transitions became less predictable after a sting event. Females spent more time on patches with higher host densities and host encounters caused a significant reduction in the leaving tendency. The giving up time was only slightly affected by host encounters. Campoplex dubitator did not demonstrate the ability to distinguish between occupied and empty host mines. The results show that C. dubitator forages more efficiently at lower host densities and this behavioural phenomenon may result in the patterns of parasitism observed in the field.     

Incidence of superparasitism in the egg parasitoid,Ooencyrtus kuvanae Howard (Hymenoptera: Encyrtidae)

The encyrtid Ooencyrtus kuvanae is a solitary parasitoid of the gypsy moth, Lymantria dispar L. (Lepidoptera-Lymantridae) that is used in biological control programmes and whose mass rearing is influenced by superparasitism. The purpose of this study was to investigate the effect of the self-superparasitism of O. kuvanae at different host densities (5, 10, 15 and 20), female ages (3 and 5 days) and durations of exposure (1 and 5 days) under various laboratory conditions (25°C?±?1°C, RH 60?±?5% and a 16:8?h light:dark photoperiod) as well as in a new laboratory host, Philosamia ricini (Danovan) (Lepidoptera: Saturniidae) of O. kuvanae. In this study, we determined the rate of egg superparasitism and adult emergence and recorded development time, longevity and body weight. Superparasitism increased with female age and the duration of exposure to parasitoids when females had access to five host eggs. Superparasitism increased the number of parasitoid offspring, but it resulted in male-biased (56.90%) progeny. Furthermore, superparasitism caused deleterious effects to the fitness of the progeny by prolonging the developmental process, and decreasing longevity. For example, we found that when four adults can emerge from one superparasitised host egg, the body size of the parasitoid offspring decreases significantly. Hence, superparasitism should be avoided when mass rearing O. kuvanae.     

Aggregation in field parasitoid populations: foraging time allocation by a population of Diadegma (Hymenoptera, Ichneumonidae)

ABSTRACT.

• 1 A field study was made of foraging time allocation by a population of parasitic wasps, Diadegma spp. (Ichneumonidae), to plants containing different densities of their hosts, the caterpillars of Plutella xylostella (L.).
• 2 The parasitoid population exhibited a clear aggregative response, spending more total time on higher density patches, which probably resulted from wasps making more and longer visits to these densities.
• 3 Despite this aggregation, positive density dependent parasitism was not found. The functional response of the Diadegma population exhibited an upper asymptote at high host densities, probably due to an increase in the proportion of time spent handling hosts, which countered the effect of aggregation.
• 4 While Diadegma may select and forage preferentially on plants with higher host density, they do not exhibit the tendency, predicted by some optional foraging models, to exploit progressively less profitable plants during a foraging bout. Some factors affecting patterns of parasitoid foraging in the field are discussed.

     

Cardinium in Plagiomerus diaspidis (Hymenoptera: Encyrtidae)

The bacterial symbiont Cardinium (Bacteroidetes) was previously implicated in the thelytokous reproduction of the parasitoid Plagiomerus diaspidis Crawford (Hymenoptera: Encyrtidae). Horizontal transmission of the symbiont among the cactus scale Diaspis echinocacti Bouché (Homoptera: Diaspididae) and its hymenopteran parasitoids has been suggested. In this study, the bacteria associated with D. echinocacti, its parasitoids P. diaspidis and Aphytis sp. (Hymenoptera: Aphelinidae), and the hyperparasitoid Marietta leopardina Motschulsky (Hymenoptera: Aphelinidae) were characterized using molecular fingerprinting techniques, and the localization of Cardinium in P. diaspidis was studied using fluorescence in situ hybridizations (FISH). Cardinium was the only bacterium found in P. diaspidis, but it could not be detected in any of the other insects tested. The symbiont was specifically located in the reproductive tissues of its P. diaspidis host.     

Discrimination of previously searched,host-free sites byMicroplitis croceipes (Hymenoptera: Braconidae)

The ability of free- ranging parasitoids to discriminate between previously visited and unvisited sites containing host kairomone (caterpillar frass) but not hosts was tested. Females of Microplitis croceipes,a host specialist and plant generalist larval parasitoid of Helicoverpa (Heliothis) zea,were allowed to fly freely in a simulated plant patch in a flight chamber. Wasps spent less time searching frass sites previously searched by themselves or by conspecifics than unsearched frass sites. In addition to chemical marking, spatial memory of visual cues was implicated as a mechanism for discriminating against self-visited, host-free sites.     

DNA barcoding of endoparasitoid wasps in the genus Anicetus reveals high levels of host specificity (Hymenoptera: Encyrtidae)

The genus Anicetus includes economically important biocontrol agents that are introduced for control of soft and wax scale insect agricultural pests (Ceroplastes spp.). Understanding of host–parasitoid associations is critical to the successful outcome of their utilization in biological control projects. However, identification of these parasitoids is often difficult because of their small size and generally similar morphological features, and hence, studies on the host–parasitoid associations. Here, nucleotide sequence data were generated from the mitochondrial COI gene and the D2 region of 28S rRNA to assess genetic variation within and between species of Anicetus occurring in China. The results of this study support the use of the COI and the D2 region of 28S rRNA gene as useful markers in separating species of Anicetus, even in cases where morphological differences are subtle. On the other hand, the COI gene is also useful in recognizing species with much variation in morphology. DNA barcoding reveals high levels of host specificity of endoparasitoids wasps in the genus Anicetus. Our results indicate that each Anicetus species is adapted to a limited set of host species, or even are monospecific in their host choice.     

Age-dependent functional response of Aphidius matricariae (Hymenoptera: Braconidae) on tobacco aphid,Myzus persicae nicotianae (Hemiptera: Aphididae)

This study was performed to investigate the age-dependent functional response of Aphidius matricariae Haliday (Hymenoptera: Braconidae) at varying densities of tobacco aphid, Myzus persicae nicotianae Blackman (Hemiptera: Aphididae). Six densities (2, 4, 8, 16, 32, and 64 numbers) of third instar nymphs of M. persicae nicotianae were daily exposed to one pair of 1-day-old A. matricariae until the parasitoid female died. Each host aphid density was replicated 10 times. The experiments were conducted at constant environmental conditions (25 ± 1 °C, 70 ± 5% RH and 16:8h L:D photoperiod). The logistic regression model demonstrated that the functional response of A. matricariae was type III in the second day and type II in the first day and from third to the end of adult parasitoid lifetime. The handling time (T_h) was lowest in the first day (0.2305 h) and highest in the sixth day (2.9296 h) of the parasitoid’s life. The searching efficiency (a) values were 0.0573, 0.0649, 0.0503, 0.0229, and 0.0077 h^?1 in the first, third, fourth, fifth, and sixth days of the parasitoid’s life, respectively. Also, the b value for type III functional response was 0.0147 in the second day. The values of maximum attack rate (T/T_h) ranged from 104.12 nymphs/24 h in the first day to 19.8 nymphs/24 h in the sixth day of parasitoid’s life. Based on the results, A. matricariae showed a high potential to control the population of tobacco aphid and the highest efficiency gained in the first half of the female parasitoid life.     

Host habitat finding and host selection of theDrosophila parasitoidLeptopilina australis (Hymenoptera,Eucoilidae), with a comparison of the niches of EuropeanLeptopilina species

Summary Decaying petioles of giant hogweed,Heracleum mantegazzianum Sommier & Levier, are used as a breeding site by six species ofDrosophila and the drosophilidScaptomyza pallida. The most numerous parasitoid species associated with this community isLeptopilina australis. BecauseL. australis was previously unknown in western Europe, we present the characters to distinguish it form its close relativeL. clavipes. Experiments on host species selection and survival ofL. australis showed that this parasitoid mainly usesD. limbata as host. Olfactometer experiments showed thatL. australis is attracted by the odour of decaying hogweed stalks, especially when these contain larvae ofD. limbata. L. australis is also strongly attracted by the odour of stinkhorns, a habitat in which it has never been found in nature.D. phalerata is the dominant fly species in stinkhorns, and is not a host ofL. australis. We offer a possible functional explanation for this unexpected habitat choice, by showing thatD. transversa andD. kuntzei, both species found to breed in fungi, are also suitable hosts forL. australis. We also discuss habitat choice with regard to a proposed phylogeny of theLeptopilina species in temperate Europe. Finally, we discuss niche overlap ofL. australis with the otherLeptopilina species.     

Competition for hosts between two hyperparasitoids of aphids,Dendrocerus laticeps andDendrocerus carpenteri (Hymenoptera: Megaspilidae): The benefit of interspecific host discrimination

The two hyperparasitoids of aphids, Dendrocerus carpenteri(Curtis) and Dendrocerus laticeps(Hedicke), differ in their interspecific host discrimination behavior: D. carpenterireadily accepts hosts for oviposition previously parasitized by D. laticeps,whereas D. laticepsoften refrains from ovipositing on hosts previously parasitized by D. carpenteri.The two species also differ in their competitive abilities: D. carpenteriis competitively superior to D. laticepswhen the time between ovipositions is 1 h. D. carpenteri's superiority probably arises from (a) the action of the venom produced by the female to paralyze the host, as evidenced by the comparison of emergence patterns from naturally vs artificially parasitized hosts, and (b) its more rapid egg development. Because of its competitive abilities, D. carpenterigains only limited benefit from discriminating interspecifically, at least when encountering a host parasitized by a competitively inferior species, such as D. laticeps.In contrast, D. laticepsgains considerable benefit from recognizing hosts previously parasitized by D. carpenteri,as the probability to produce offspring from such hosts is greatly reduced.     

Effects of parasitism by Asobara tabida (Hymenoptera: Braconidae) on the development,survival and activity of Drosophila melanogaster larvae

The impact of parasitism by Asobara tabida on Drosophila melanogaster larval development, survival features and larval activity has been investigated using two strains of the parasitoid. The successful parasitism rate of the A1 strain was four times greater than that of the WOPV strain. Both strains induced equivalent mortality rates but hosts parasitized by A1 predominantly died as pupae. The time necessary for the host pupariation and emergence, and the larval weight at 72, 96 and 120 h post-parasitization were measured. Parasitized larvae exhibited longer periods of development and lower weights than controls, especially when parasitized by A1. These results suggest that hosts underwent physiological costs varying with respect to the outcome of the parasitic relationship. Of the parasitoid factors possibly responsible for these costs, we examined venoms for their impact on host mortality. Artificial injections of WOPV venoms induced higher mortality rates than did A1 venoms. Venoms were also found responsible for the induction of a transient paralysis, naturally occuring after parasitization. Again, the strongest effect was observed after parasitization by WOPV or injections of its venoms. This study gives new insights into the intriguing features of A. tabida and constitutes the first report of the paralysing properties of the venoms.     

Comparison of the suitability of Liriomyza chinensis and L. trifolii (Diptera: Agromyzidae) as hosts for Neochrysocharis okazakii (Hymenoptera: Eulophidae)

Effective parasitoid production or mass-rearing is one of the key components in practicing biological control with parasitoids. Selection of host species for rearing parasitoids is a major approach to improve the production efficiency. The stone leek leafminer Liriomyza chinensis (Kato) is a destructive pest of onion crops in many Asian countries, which is difficult to control with chemicals. The present study examined whether the production of Neochrysocharis okazakii Kamijo, a promising native biological agent of L. chinensis, could be effective if kidney bean-Liriomyza trifolii (Burgess) system was used as an alternative rearing procedure. The suitability of L. chinensis and L. trifolii as hosts of N. okazakii was investigated in the laboratory. Neochrysocharis okazakii completed its development on both two host species, and the total development time was similar on these hosts. Longevity of N. okazakii females provided with L. chinensis was longer than those on L. trifolii. There were no significant differences in fecundity and offspring sex ratio when females had been provided with these two host species. The adult parasitoids emerged from L. chinensis were significantly larger than those from L. trifolii. However, the intrinsic rate of increase was higher, and mean generation time was lower, for L. trifolii than L. chinensis. Thus, mean net reproductive rate (Ro) was higher when L. trifolii was used as host. Although the two host species were equally suitable as host for N. okazakii, our findings suggested that L. trifolii and kidney bean is an ideal system for N. okazakii production.