The role of host species, age and defensive behaviour on ovipositional decisions in a solitary specialist and gregarious generalist parasitoid (Cotesia species)

The main objective of this study was to determine the extent to which host acceptance behaviour as related to host species, age, and defensive behaviour might explain the differences in host use that exist between two congeneric and sympatric species of parasitic wasps. Cotesia glomerata (L.) (Hymenoptera: Braconidae) is gregarious and generalist on several species of Pieridae, whereas C. rubecula (Marshall) is solitary and specific to Pieris rapae (L.). Cotesia species differed in their responses to host species (P. brassicae (L.), P. napi (L.) and P. rapae) and developmental stage (early and late 1st, 2nd and 3rd instars). In no-choice tests, host acceptance by C. rubecula was higher for p. rapae and females did not distinguish among the 6 host ages. In contrast, when foraging for P. brassicae and P. napi, C. rubecula females more readily attacked early first instar. Cotesia glomerata showed a higher degree of behavioural plasticity towards acceptance of Pieris host species and host age than did C. rubecula. Cotesia glomerata females parasitized the three Pieris species and showed higher acceptance of first and second instars over third instar. Oviposition success was also influenced by host defensive behaviour. The frequency and the effectiveness of defensive behaviour rose with increasing age of the host, P. brassicae being the most aggressive Pieris species. Furthermore, the mean duration of C. glomerata oviposition was significantly reduced by the defensive reactions of P. brassicae, which would likely affect parasitoid fitness as oviposition time is positively correlated to clutch size in C. glomerata. Acceptance frequencies corresponded well to field reports of Pieris-Cotesia associations and to patterns of parasitoid larval performance, suggesting that the acceptance phase might be used as a reliable indicator of Cotesia host-specificity.     

The influence of plant species on attraction and host acceptance inCotesia glomerata (Hymenoptera: Braconidae)

Females of the larval parasitoidCotesia glomerata (L.) use plant-associated cues to locate their lepidopteran host,Pieris rapae L. In this study we investigated the influence of four host plant species,Brassica oleracea var.acephala (‘Vates’ kale),Tropaeolum majus (nasturtium),Lunaria annua (honesty), andCleome spinosa (spider flower), on two components of the host selection process inC. glomerata, namely, attraction and host acceptance. Choice tests in a flight tunnel showed that parasitoids were attracted to some host plant species more than to others in the absence of host larvae.B. oleracea was the most attractive plant species, followed byL. annua, T. majus, andC. spinosa. In previous studies it was shown thatB. oleracea carries highly suitable hosts forC. glomerata and that, in the field, parasitization rates on this plant were the highest. When host larvae were reared on the four host plant species and then transferred to a common substrate (B. oleracea var.capitata, cabbage), plant species that had served as diet for the hosts did not have a significant effect on acceptance for parasitization. Thus, parasitoids were attracted to host plant species differentially, but they did not discriminate among host larvae based on the dietary history of their hosts. ForC. glomerata, it appears that phytochemistry mediates host selection more by influencing parasitoid attraction than it does by affecting host acceptance.     

Trade-offs in larval performance on normal and novel hosts

The evolution of host specialization in phytophagous insects is generally thought to involve genetic trade-offs that prevent individuals from maximizing fitness simultaneously on two or more hosts. Several hypotheses, however, have suggested that trade-offs may not be evident in experiments comparing larval performance on normal and novel hosts. Tests on survivorship, growth rate, and pupal mass among families of the swallowtail butterfly Papilio oregonius on its normal host and on a novel host provide support for these hypotheses, although they do not discriminate among them. Families differed in their relative performance on the hosts, but there was no evidence of a negative genetic correlation between hosts for any of the measures of performance. In addition, there were no correlations among the different measures, corroborating an earlier result suggesting that these different components of performance in the P. machaon species group are under at least partially separate genetic control. These results and similar results published for other insects have now produced a body of studies indicating that genetic trade-offs in individual components of larval performance may not be a major factor preventing shifts onto novel host plants. Trade-offs leading to the evolution of host specialization are more likely to involve coordination among the various components of performance together with ecological factors that allow higher fitness on one host than on others.     

Zombie fire ant workers: behavior controlled by decapitating fly parasitoids

Laboratory observations were conducted on four separate red imported fire ant, Solenopsis invicta, colonies that contained workers parasitized by the decapitating fly, Pseudacteon tricuspis. Parasitized S. invicta workers remained inside the nest during parasitoid larval development and left the nest approximately 8 – 10 hours before decapitation by the parasitoid. When parasitized ants left the nest, they were highly mobile, were responsive to tactile stimuli, and showed minimal defensive behavior. Ants ultimately entered into a grass thatch layer, where they were decapitated and the fly maggots pupariated. This study reveals that parasitized ants exhibit behaviors that are consistent with host manipulation to benefit survival of the parasitoid. Received 9 November 2006; revised 26 January 2007; accepted 7 February.     

Sex Allocation by a Parasitoid Wasp (Hymenoptera: Ichneumonidae) to Different Host Species: A Question for the Mechanism of Host Size Estimation

Sex allocation by the polyphagous solitary pupal parasitoid wasp Pimpla luctuosa Smith to a small host species, Galleria mellonella (L.), and a large host species, Mamestra brassicae L., was investigated to test whether female wasps responded to hosts of different sizes across different host species. In the experiments, both host species were presented to each test female wasp. Primary and secondary sex ratio experiments revealed that female wasps laid more female eggs in larger pupae of each host species, indicating that female wasps recognized size differences within host species. The wasp sex ratio (male ratio) from M. brassicae, however, was much higher than that expected on the basis of the sex ratio curve from different-sized G. mellonella. Larger hosts of each host species yielded larger wasps, indicating that the host size estimation by female wasps across different host species was incomplete or was not simple. These results suggested that P. luctuosa evaluated host size not only by physical measures such as dimension but also by other unknown measures. A possible explanation for the adaptiveness of different sex ratio responses by Pimpla luctuosa to different host species was discussed.     

Studies in parasitic watermolds of Kumaun Himalayas: The host range of five species of olpidiopsis

The host range of five species of Olpidiopsis in some species of Achlya, Aphanomyces, Brevilegnia, Isoachlya, Saprolegnia, Thraustotheca and Pythium was studied. Species were different in their host range.     

Host recognition byPimpla instigator F. (Hymenoptera: Ichneumonidae): Preferences and learned responses

This study identifies some previously unreported tactile and visual cues used by the pupal parasitoid Pimpla instigatorF. (Ichneumonidae) to recognize potential hosts. Paper cylinders were presented to the wasps as simple models of lepidopteran pupae. Acceptance of these models was evaluated by determining the frequency with which the wasps punctured the cylinders with their ovipositors. The length of the cylinders did not influence acceptance of the models; however, both surface texture and structural modifications to the ends of the cylinder did affect the frequency of punctures. Smooth cylinders were punctured more often than roughened cylinders, and cylinders with closed ends were frequently punctured, whereas open-ended cylinders were consistently rejected. The wasps also discriminated between blue and yellow cylinders and could be trained to associate blue or yellow with the presence of hosts. Preferences were established during a single 90- min training period and persisted for at least 4 days following training.     

Prefeeding Behavior of the Crucifer Flea Beetle, Phyllotreta cruciferae, on Host and Nonhost Crucifers

The prefeeding behaviours of adult crucifer flea beetles, Phyllotreta cruciferae (Coleoptera: Chrysomelidae: Alticinae), were determined on seedlings of the host plant, Brassica napus, and compared to behaviors on seedlings of the nonhost crucifers, Crambe abyssinica, Sinapis alba, and Camelina sativa. Three stages of prefeeding behaviour, i.e., acclimation, stimulation, and initial feeding, were distinguished through observation of filmed beetles. Both antennal and tarsal chemoreceptors are important in determination of host plant quality by the crucifer flea beetle. The results of this study suggest that the sequence of prefeeding behaviors plays a crucial role in the onset of feeding. Differences in time spent on plant tissue and the frequency and duration of prefeeding behaviors provide insight into possible mechanisms of resistance to flea beetles in the non-Brassica crucifers. The nonpreferred hosts C. abyssinica and S. alba contain deterrent phytochemicals that partially inhibit feeding. These deterrent compounds appear to be volatile in nature in S. alba but nonvolatile in C. abyssinica. CFB resistance in the nonhost C. sativa may result from either the presence of repellent or the absence of stimulatory volatile phytochemicals.     

Role of some epigenetic factors influencing the host suitability of Myzus persicae for the parasitoid Aphidius colemani

When a host is stung by a parasitoid female in the aphid-aphidiid association Myzus persiae Sulzer-Aphidius colemani Viereck, four host responses have been observed: 1) a host develops into a mummy, 2) it dies very soon after it was stung, 3) it develops a cellular immune response, 4) it shows no apparent perturbation subsequent to the sting. The ratios of the responses are clearly determined by the type, the number and the rank of the sting and also by the experience of the female. Some assumptions concerning the cause of the host response are discussed.

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Résumé Le devenir d'un puceron piqué par une femelle parasitoïde dans l'association Myzus persicae Sulzer-Aphidius colemani Viereck est clairement conditionné par différents facteurs associés à la séquence de piqûre. Quatre devenirs ont été régulièrement observés parmi tous les lots d'hôtes piqués; il s'agit d'une mommification classique aboutissant à l'émergence d'un parasitoïde adulte, d'une mort précoce, de l'apparition de profondes modifications anatomiques et physiologiques ou enfin, d'un développement apparemment sain du puceron. Les proportions de ces devenirs varient avec la nature, le nombre, le rang de la piqûre, ainsi qu'avec le passé de la femelle avant l'expérience. Par comparaison avec une piqûre classique, une piqûre peu profonde réduit le nombre de momies formées, mais surtout élimine toute mortalité avancée et favorise le devenir sain. Lorsqu'on augmente de un à trois le nombre de piqûres reçues par l'hôte, la probabilité d'échapper en apparence à un effet quelconque de la piqûre diminue, alors qu'en parallèle, c'est surtout celle de la mommification qui croît. Il existe de plus pour certaines femelles, une relation entre le rang de la piqûre et le devenir de l'hôte. Enfin, si une femelle a dans un premier temps piqué un puceron altéré, près de 90% des pucerons normaux qui sont ensuite piqués évoluent en momies. A partir de ces résultats, certaines hypothèses concernant la cause des différents devenirs sont avancées.

     

Larval dispersal from potential hosts within a population of a generalist herbivore, Choristoneura rosaceana

The dispersal behavior of Choristoneura rosaceana (Harris) (Lepidoptera: Tortricidae) first instar larvae was studied in the laboratory. The objectives were to investigate the proximal factors influencing larval dispersal and to establish whether a correspondence exists between larval host acceptance and performance. A dispersal bioassay was validated by demonstrating the presence of a positive correlation between larval host acceptance in the laboratory and in the field. Larval age and family origin, as well as host species attributes were shown to influence larval dispersal rates. Seasonal changes in host plants slightly changed the rank order of larval host acceptance. Leaf texture and the availability of refuges on host plants seemed to be important factors influencing the rate of larval dispersal. Plant odor appeared to be used by the larvae to locate leaves. Nitrogen content of plant species corresponded to larval dispersal rates, but the cause of this association is unclear. Larval dispersal did not match host suitabilities as measured by larval performance. The relationship between host preference and suitability in the obliquebanded leafroller is discussed in an ecological and evolutionary perspective.     

Selectivity mechanism of Anoplophora glabripennis on four different species of maples

Anoplophora glabripennis (Motsch.) is a woodboring beetle that is native to China. For a long time, it caused great losses in the economy and ecology of northwest China. Attractants are often used to control insects. The volatiles emitted from the host plant play an important role for insects in finding their target. To explore the mechanism of selectivity to different host plants, the response of Anoplophora glabripennis to four different host plants was investigated, which included Acer negundo L., Acer mono Maxim., Acer truncatum Bunge. and Acer platanoides L., and the compounds in the profiles of volatiles were identified from these species. The olfactory responses of Anoplophora glabripennis to the odors of different plants showed preference for certain host plants: Acer negundo, Acer mono and Acer truncatum. The attraction of Acer negundo and Acer mono was significantly different (p<0.05). The attraction of Acer negundo to the insects was stronger than to Acer mono. Acer platanoides neither attracted nor repelled the insects. Compounds in the profiles of volatiles from the above four species were identified and quantified by gas chromatography-mass spectrometry (GC-MS) equipped with a CP-4020 termodesorption and cold trap (TCT) device. The constituents of volatiles and the relative concentrations were different in the four host species. The amount of ketones, alcohols and aldehydes in the four plants showed the same order: Acer negundo<Acer mono<Acer truncatum<Acer platanoides, while that of alkanes and esters was quiet different: Acer negundo L.>Acer mono Maxim.>Acer truncatum Bunge.>Acer platanoides L.. 1-penten-3-ol, ocimene and trans-Germanylacetone were repellent to Anoplophora glabripennis. 1-penten-3-ol and trans-gerranylacetone were identified in Acer platanoides, and Ocimene was the most attractive to Anoplophora glabripennis among these species. The extent of feeding damage caused by Anoplophora glabripennis differed among four species. The sequences was Acer negundo>Acer mono>Acer truncatum>Acer platanoides. The epidermal hairs of the four host plants revealed that the extent of damage was related to the physical characteristics of the host plants. __________ Translated from Acta Ecologica Sinica, 2006, 26(3): 870–877 [译自:生态学报]     

Comparative responses of two sympatric parasitoid cynipids to the genetic and epigenetic variations of the larvae of their host, Drosophila melanogaster

Infestation of larvae of Drosophila melanogaster by both Leptopilina boulardi and L. heterotoma (Hymenoptera, Cynipidae: Eucoilidae) varies according to within-population genetic variations in the hosts. L. heterotoma larvae thrive better than L. boulardi and developmental success of both parasitoids varies according to the host's genotype. Crowding in hosts improves success rate of both species, that of L. boulardi then being equal to that of L. heterotoma.

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Résumé Les résultats de l'infestation des larves de D. melanogaster par les Cynipides Leptopilina boulardi et L. heterotoma varient selon le génotype des hôtes et leur état nutritionnel. L'analyse génétique de la population hôte par la méthode des lignées isofemelles montre que le degré d'infestation (pourcentage de larves effectivement parasitées dans des tests standidardisés) varie significativement entre lignées. Le taux de succès du développement parasitaire (pourcentage d'hôtes parasités fournissant un parasite adulte) est plus élevé chez L. heterotoma que chez L. boulardi et varie fortement entre lignées d'hôtes. Les variations chez les deux parasites sont corrélées.La sous-alimentation des larves parasitées augmente le succès du développement des deux parasites et celui de L. boulardi devient alors égal à celui de L. heterotoma.La réponse à l'infestation par les deux Cynipides n'est pas uniforme au sein de la population hôte et varie en fonction de l'abondance des ressources nutritionnelles de ce dernier.

     

寄主植物对桃蛀螟生长发育及产卵选择行为的影响

为明确寄主植物对桃蛀螟生长发育及产卵选择行为的影响,利用实验种群生命表和二项产卵选择试验,研究了玉米、大豆、棉花和桃等4种寄主植物对桃蛀螟种群生长发育及产卵选择性的影响。结果表明:取食棉花的桃蛀螟幼虫存活率最低、幼虫历期最长,取食玉米的幼虫存活率最高、幼虫历期最短,取食桃和大豆的幼虫存活率和历期居于棉花处理组和玉米处理组之间;玉米处理组的桃蛀螟化蛹率、蛹重和蛹历期均为最高,棉花处理组为最低,大豆和桃处理组的这些参数均显著小于玉米处理组而大于棉花处理组;发育至成虫后,取食玉米的桃蛀螟羽化率显著高于其他3个处理组;取食桃的桃蛀螟成虫寿命(雌虫和雄虫)及个体发育历期均显著高于其他3种处理组;同时取食桃的桃蛀螟单雌产卵量最高,其次是玉米处理组,两者均显著高于大豆和棉花处理组。二项产卵选择试验结果显示,桃蛀螟雌蛾在棉花和玉米处理组、玉米和大豆处理组或棉花和大豆处理组间的落卵量差异不显著;但在包含桃的处理组中,桃蛀螟在棉花、玉米或大豆处理区的落卵量均显著高于桃处理区。上述结果表明,供试4种寄主植物中,桃蛀螟偏好在棉花、玉米和大豆上产卵,其中玉米对桃蛀螟的适合度相对较高,棉花对桃蛀螟的适合度相对较低...     

Host population density influence on host acceptance inTrichogramma

In 7Trichogramma species (Hymenoptera, Trichogrammatidae) the percentage of females, parasitizing at least one host, directly depends on the number of host eggs.Trichogramma females that refusedSitotroga eggs will still oviposit in natural hosts. These refusing females were yet active, moved in test tubes and sometimes contacted the host. It seems that the sequence of behavioural reactions resulting in parasitization is interrupted at the stage of arrestment and host recognition. Host density within a habitat proved to be an important factor in host acceptance. Possible mechanisms that formed the basis of the observed effect (behavioural response to host kairomones, the learning ability, endocrine processes) are discussed.

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Résumé En utilisant l'hôte de laboratoire (Sitotroga cerealella Oliv.) nous avons démontré qu'une partie des femelles refuse la parasitation. L'analyse de la succession des actes constitutifs de la parasitation montre que celle-ci est interrompue au moment de l'acceptation. Le pourcentage des femelles parasitante est en dépendance directe du nombre des ufs de l'hôte. Les résultats de cette étude suggèrent que l'acceptation de l'hôte par le parasitoid est finction de la densité de population de celui-là. Les mécanismes possibles de cette dépendance (la réaction aux kairomones, l'apprentissage, les modification endocrines) sont discutés.

     

Host location and discrimination mediated through olfactory stimuli in two species of Encyrtidae

The role of olfactory stimuli in host detection and evaluation was studied in two encyrtid Hymenoptera. The first, Epidinocarsis lopezi De Santis, is a monophagous parasitoid of the cassava mealybug Phenacoccus manihoti Matile-Ferrero, itself feeding exclusively on cassava, Manihot esculenta Crantz. The second, Leptomastix dactylopii Howard, is a monophagous parasitoid of the Citrus mealybug, Planococcus citri Risso, but this latter is highly polyphagous. The behaviour of females of both parasitoids (attaction and locomotion) was compared in a tubular olfactometer for the odours of their respective hosts on cassava and poinsettia. Tests were made using: 1) healthy host-plant alone; 2) host-plant infested with unparasitized mealybugs; 3) unparasitized mealybugs only; 4) host-plant infested with parasitized mealybugs and 5) parasitized mealybugs only. Only E. lopezi was attracted by the odour of the host-plant alone, but both species were attracted by the odour of an infested host-plant and that of unparasitized mealybugs. The odour of parasitized mealybugs, alone or on host-plant, induced an undirected activity. The attraction of E. lopezi to the odour of the host-plant alone could be linked to the monophagous diet of its host, whereas the attraction of the two species of parasitoids to the odours of infested host-plants and unparasitized mealybugs could be due to the fact that both parasitoids are specialists. The behavioural response of both species to the odour of parasitized mealybugs revealed a new aspect in host discrimination: the identification of parasitized hosts could be partly mediated through olfactory stimuli, and not only through gustatory stimuli.     

沙门菌效应蛋白对宿主细胞的影响及分子机制

沙门菌(Salmonella spp.)作为胞内病原菌,通过侵入宿主细胞,导致人类和多种动物感染疾病。在与宿主细胞的长期斗争中,沙门菌进化出多种机制来逃避宿主的监视与防御,从而完成侵入并生存增殖的过程。尽管一些效应蛋白靶向的宿主因子已经被发现,但大多数效应蛋白的靶点尚且未知。本文综述了沙门菌效应蛋白对宿主细胞生理活动的影响,包括对细胞骨架的变化、炎症应答、胞膜修饰和滤泡的胞内移动现象及其分子机制进行阐述。     

Host examination walk and oviposition site selection ofTrichogramma minutum: Studies on spherical hosts

The host examination behavior of the parasitoid wasp Trichogramma minutumon spherical Manduca sextahosts is described. The mean walking speed during host examination was 0.64 ± 0.03 mm s ^–1 and is independent of wasp size. The paths taken by the wasps are not evenly distributed over the host surface; the majority of time is spent below 45 ° latitude. The distribution of oviposition sites is also nonrandom with respect to latitude and is not influenced by phototaxic and geotaxic responses. The initial transit made by the wasps over the host surface is a straight path which frequently passes across the highest point on the host. The length and duration of the initial transit are independent of wasp body length. However, stride length and stepping rates are proportional to wasp body length, and small wasps take more steps to complete their initial transit. The roles of the examination walk in host recognition and host volume measurement by Trichogrammaare also discussed.     

Host nest preference and nest choice in the cuckoo paper wasppolistes sulcifer (Hymenoptera: Vespidae)

Polistes sulcifer is a cuckoo paper wasps, an obligate social parasite which must usurp a colony of another species in order to reproduce. Field data show thatP. sulcifer females usurp exclusively nests belonging to one species only (P. dominulus). Moreover, they are more frequently found on large and puparich nests. A series of laboratory trials, in which parasite females were offered a binary choice of nests with different characteristics, confirm both the species specificity betweenP. sulcifer andP. dominulus and the parasite's preference to usurp larger nests containing pupae. The data support the hypothesis thatP. sulcifer females choose between available nests. The biological meaning of these findings is discussed.     

Response ofChelonus blackburni [Hym.: Braconidae] to different ages and densities of potato tuber moth eggs

The response of an efficient egg-larval parasitoidChelonus blackburni Cameron to different ages and densities of potato tuber mothPhthorimaea operculella (Zeller) eggs was studied in a laboratory system. The parasitoid accepted 0–1, 1–2 and 2–3 day old eggs for parasitization. However, the eggs belonging to the first two age groups were significantly more acceptable when compared to the last age group. At low host density levels of 2 and 5 eggs per parasitoid, parasitoid emergence was zero. On increasing the host density, percent progeny production increased till a plateau was reached at a parasitoid-host ratio of 1∶50. This ratio thus proves to be ideal for obtaining maximum percent progeny production in the case of 0–1 and 1–2 day old eggs. Further increase in host density did not result in any significant increase in percent progeny production.