Analysis of solitariness in a parasite—host system (Muscidifurax raptor,Hymenoptera: Pteromalidae—Ceratitis capitata,Diptera: Tephritidae)*

Abstract. 1. The behaviour of the parasite Muscidifurax raptor Girault and Sanders was studied when searching for hosts, puparia of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann). At low density females tend to avoid encountering parasitized hosts. This tendency decreases as density of searching females increases. 2. The proportional avoidance of superparasitism was calculated and the effect of increasing number of encounters per host on this parameter was analysed. 3. The mechanisms of solitariness were studied. These mechanisms include: outer marking of the hosts by the female parasite and deliberate physical attack of the newly hatched larvae to eliminate as yet unhatched eggs. 4. In cases of intraspecific competition between larvae, young first or second instar larvae usually have the advantage over older larvae.     

Effect of temperature and parasite density on three species ofAphytis (Hymenoptera: Aphelinidae), parasitising California red scale

Summary Three species ofAphytis parasites of California red scale,Aonidiella aurantii (Maskell) were each confined at different densities with approximately equal numbers of scale insects at several constant temperatures to determine the effect of these factors on progeny production and distribution and the search rate. Egg location on the host body by the parasites was unaffected by temperature or parasite density.A. melinus laid its eggs both dorsally and ventrally in equal proportions whileA. lingnanensis andA. chrysomphali laid their eggs ventrally. Progeny production byA. melinus andA. lingnanensis increased at the higher temperature; that ofA. chrysomphali did not. Unlike the other species,A. chrysomphali failed to oviposit at 32°C. Although increasing parasite density reduced progeny production in bothA. melinus andA. lingnanensis, they were able to maintain an almonst constant search rate. This was due to their ability to distribute their eggs among the hosts more regularly at the higher parasite densities. While the mechanism of this process is easy to understand forA. melinus which behaved as a gregarious parasite, it is unclear forA. lingnanensis, which is almost a solitary parasite. The progeny production and the search rate ofA. chrysomphali dropped significantly with increasing parasite density.     

Functional response to host density by the egg parasiteTrichogramma pretiosum

The effect of host density on parasitism byTrichogramma pretiosum Riley was studied by exposing groups of 150, 300, 600 or 1200 eggs of potato tuber moth to 2, 4 or 8 female parasites per group. The parasite exhibited a type 2 functional response. As host density increasedT. pretiosum parasitised more hosts, but at a decreasing rate. The attack coefficient (a′) decreased as parasite density increased, whereas the handling time (T _h ) remained almost constant. The search rate (a) decreased with increasing host density.T. pretiosum responded to increasing host density by increasing the number of its encounters with hosts and the number of hosts it parasitised only up to host density of 300 when the parasite density was 2 and up to host density of 600 when the parasite densities were greater and then remained almost constant. The observed incidence of parasitism was higher than that expected on the assumption that the parasites behaved the same at higher host densities as at the lowest. When parasite density was raised from 2 to 8 females per group the percentage of female progeny fell from about 73 to about 48%. A 2-fold increase in the number of female progeny was observed when parasite density was reduced from 8 to 2 and also when the host density was raised from 150 to 1200 eggs.     

Effect of hosts and parasite density on the egg parasiteTrichogramma pretiosum [Hym.: Trichogrammatidae]

When females ofTrichogramma pretiosum Riley were confined with host eggs at a density of 2/150 eggs, they produced 12 times more female progeny on eggs of potato tuber moth than on eggs ofHeliothis armigera (Hübner) and 13,6 times more on eggs ofSitotroga cerealella (Olivier) than on eggs ofHeliothis. At a density of 4/150 eggs, the correspondent figures were 13 and 8 times. The percentage emergence fromHeliothis eggs was from 0,29 to 0,14 times as great as from tuber moth orSitotroga. From 15 to 140 times more runts were observed amongTrichogramma fromHeliothis eggs than among those from tuber moth eggs and 8 times more thant among those fromSitotroga eggs. This may explain the low recoveries in South Africa ofT. pretiosum in eggs ofH. armigera collected in cotton fields after mass liberation of the parasite. An increase in parasite density from 1/300 eggs to 16/300 eggs resulted in a decrease from 29 to 14 in the hosts parasitised per female, a decrease in the proportion of female progeny from 72 to 39%, a decrease in the female progeny per female from 18 to 4,8, and an increase in the proportion of runts from 2,4 to 12,4%. It is suggested that in mass culture ofTrichogramma unduly high parasite densities should be avoided in order to reduce the effect of mutual interference and raise the output of female progeny.     

Population dynamics ofTelenomus fariai (Hymenoptera: Scelionidae), a parasite of Chagas' disease vectors IX. Larval competition and population size regulation under laboratory conditions

A series of experiments were carried out with the endophagous egg parasite Telenomus fariai on its host Triatoma phyllosoma pallidipennis to determine the possible role of intraspecific competition by the parasite progeny in population regulation of the parasite. Eight parasite densities (1, 3, 5, 10, 20, 30, 40, and 50 individuals per vial) were used, and the design of sequentially sacrificed replicates applied. Survivorship curves for each density indicated smaller number of progeny per host at higher densities, and the shapes of the curves suggested a relatively early mortality process.Morris' linear regression technique for determining within-generation density-dependence was used, and the results showed that only larval mortality could be identified as density dependent. The same technique applied within the larval stage proved that only mortality of larvae in their second, third, and fourth day of development were responsible for population regulation. The applicability of the technique, as well as the relevance of the results for natural population, is discussed.     

Competition and host size mediate larval anuran interactions with trematode parasites

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Effects of parasite density and host availability on progeny production byBiosteres (Opius) longicaudatus, [Hym.: Braconidae], a parasite ofAnastrepha suspensa [Dip.: Tephritidae]

Progeny production ofBiosteres (Opius) longicaudatus Ashmead, a larvalpupal parasite of the Caribbean fruit fly,Anastrepha suspensa (Loew) was affected by host availability, previous ovipositional experience, and parasite density and age. Parasitization rates were evaluated in 24.5 cm³ ovipositional cages at parasite densities of 25, 125, and 250 male-female pairs by exposingB. longicaudatus adults to (a) 500A. suspensa larvae for a 24 h period or (b)ad libitum host larvae for each of the 14 days following eclosion. The mean numbers of parasite progeny produced at the 25, 125, and 250 densities were 1076, 1896, and 2038, respectively. The number of progeny produced per surviving female parasite was inversely proportional to the adult parasite density and relatively more female progeny were produced as the adult parasites aged. Host mortality was significantly higher among parasitized larvae. Maximum rearing efficiency was achieved at the 125 density.     

Host-attacking behavior of a eulophid parasite,Kratochviliana sp., to the leaf mining host,Phytomyza ranunculi (Diptera: Agromyzidae) during its stay on the leaf

The present paper studies how the female parasite of Kratochviliana sp. visits and attacks its host larvae of Ranunculus leaf mining fly, P. ranunculi at a single leaf visit. The parasite visited its hosts at random on the leaf. The frequency of host visits was independent of the host density and the proportion of hosts survived from the parasite attack, in a leaf and its distribution was expressed as a single straight line. It almost always attacked living hosts at the first host visit after isolated from them for one day but with the rate of about 0.5 at the subsequent visits. In consequence, the relationships of the number of host attacks and killed hosts to the host density drew satulated curves in each. A model of host attack by this parasite at its single leaf visit was formulated by modifyingBakker et al.'s model (1972) basing upon these observations and the attack avoidance by the parasite to already attacked hosts previously reported.     

Taking a chance on moths: oviposition by Delia flavifrons (Diptera: Anthomyiidae) on the flowers of bladder campion, Silene vulgaris (Caryophyllaceae)

Abstract.

• 1 Delia flavifrons Zetterstedt (Diptera: Anthomyiidae) visits flowers of Silene vulgaris (Moench) Garcke (Caryophyllaceae), where the adults feed, mate, lay their eggs, and the larvae feed on developing seeds. The objective of the study was to examine how an ovipositing female fly assures a food resource for her progeny.
• 2 Ovipositing females preferred young, non-pollinated flowers over older pollinated ones. The flies did not pollinate the flowers and survival of the larvae depended on the flowers being pollinated by moths.
• 3 Flowers containing fly eggs were pollinated more often than expected from chance, probably as a result of both flies and moths visiting particular flowers.
• 4 Eggs were laid singly, and multiple oviposition occurred randomly. Although most eggs hatched, only about half produced larvae that made their way into the fruits. As a result, the probability of competition arising from multiple oviposition may be reduced to such an extent that selection does not favour females that avoid flowers with conspecific eggs.
• 5 Moth larvae of the noctuid genus Hadena also feed on the seed pods of S. vulgaris and will kill any fly larvae they encounter. However, there was no deviation from random oviposition by the flies in relation to eggs laid by the moths, but the competitively weaker fly usually started to lay eggs towards the end of the moth's egg-laying period.
• 6 The relationship between Delia flavifrons and Silene vulgaris superficially parallels that for known pollinator/predator systems, but floral adaptations to hypothetically pollinating flies seems not to have taken place.

     

Local diversity reduces infection risk across multiple freshwater host‐parasite associations

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Asymmetric larval competition between two species of solitary parasitoid wasps: the influence of superparasitism

Abstract.

• 1 We test the hypothesis that a solitary parasitoid wasp may gain in fitness if she lays more eggs in a host.
• 2 Using heterospecific superparasitism (=multiparasitism) between the solitary aphid parasitoids, Aphidius smithi Sharma & Subba Rao and Ephedrus californicus Baker, we show that (i) a superparasitizing female's chance that her offspring will survive competition is an increasing function of egg density, and (ii) survival among same-aged larvae is independent of the oviposition sequence.
• 3 These findings on asymmetric larval competition provide indirect evidence that supports two fundamental, but untested, assumptions underlying models of adaptive superparasitism between conspecific wasps.

     

Egg size affects larval performance in a coleopteran parasitoid

Abstract 1. Optimal progeny size models assume that the more eggs a female produces, the lower the amount of resource allocated per egg. As egg size generally correlates with the fitness of the emerging immature, this trade‐off can be expressed as a choice between the production of numerous low quality or fewer high quality progeny. 2. The first‐instar larvae of the coleopteran parasitoid Aleochara bilineata have to search for and parasitise dipteran pupae. The present study found a positive correlation between egg size and larval weight, but not between egg size and development time. Larger first‐instar larvae survived longer, were more active, and found and parasitised their host more rapidly. 3. Female A. bilineata may invest smaller larvae in conditions of high host density and low intraspecific competition, but investing fewer, larger larvae would bring them more fitness when hosts are scarce and competition high.     

Age‐specific maternal effects interact with larval food supply to modulate life history in Coleomegilla maculata

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Superparasitism and mutual interference in the egg parasitoid Anagrus delicatus (Hymenoptera: Mymaridae)

Abstract.

• 1 In nature, interference among Anagrus delicatus (Hymenoptera: Mymaridae) parasitoids reduced the per-capita number of hosts parasitized. Interference increased with parasitoid density.
• 2 Anagrus delicatus did not avoid parasitizing hosts that had recently been parasitized by conspecific wasps. Evidence indicated that this superparasitism was largely a random process, increasing with the ratio of parasitized to unparasitized hosts.
• 3 Individual parasitoid efficiency, the number of hosts killed per wasp per unit time, decreased with increasing wasp density. This occurred whether wasps searched the patch together (simultaneously) or one by one (sequentially), and was the result of an increase in time spent superparasitizing hosts at higher wasp density. This is known as indirect mutual interference.
• 4 Increasing numbers of parasitoids together on the same patch caused a significant decline in the rate and per-capita number of hosts parasitized. However, there was not a correspondent decline in searching efficiency with increasing wasp density (i.e. no direct mutual interference).
• 5 These forms of parasitoid density dependence should contribute to the stability of the host—parasitoid interaction.

     

Larval cannibalism during the late developmental stages of a facultatively gregarious encyrtid endoparasitoid

• 1 The larvae of many gregarious parasitoid species are usually non‐aggressive when they develop in or on a host, but those of Metaphycus flavus are one of the few exceptions known. Herein we describe their aggressive behaviour and the conditions under which it occurs, using observations in which larval development and physical conflict within parasitised and superparasitised hosts were mapped daily.
• 2 Metaphycus flavus larvae often engaged in physical conflict that resulted in consumption of the losing larvae (= cannibalism ) in superparasitised hosts, whereas such conflict and consumption occurred rarely when a single brood developed in a host.
• 3 Cannibalism among M. flavus larvae only occurred after the host resources had become scarce. Typically it occurred after the sixth day of development (fourth‐instar larvae) when the larvae in a clutch had separated from their aeroscopic plate and were freed of their attachment to the host's cuticle.
• 4 Female larvae in the initial clutch appeared more aggressive than male larvae when a second clutch was allocated 4 h after the first clutch. The probability of a larva being attacked and consumed by a brood mate increased as the number of larvae increased in the host. This partial tolerance might allow the members of the initial brood to defend themselves from offspring of a superparasitising female (= competitors ). Such post‐ovipositional regulation of brood size might be interpreted as high‐density intolerance among female offspring.

     

The effect of superparasitism on development of the solitary parasitoid wasp, Venturia canescens (Hymenoptera: Ichneumonidae)

Abstract.

• 1 The effects of superparasitism on the rate of development, adult size and mortality of Venturia canescens (Hymenoptera: Ichneumonidae) were investigated. Parasitoids were reared from third (L3) and fifth (L5) instars of one of its hosts, Plodia interpunctella (Lepidoptera: Pyralidae) containing one, two or four parasitoid eggs.
• 2 Superparasitism increased the development time of Venturia reared from both instars, but the developmental delay was more evident in wasps from L5 hosts.
• 3 The size of parasitoids from L3 hosts was unaffected by egg number, but wasps from both superparasitized L5 treatments were significantly smaller than those from singly parasitized hosts.
• 4 Parasitoid mortality was significantly higher in L5 than L3, but within instars did not differ significantly with egg number.
• 5 The results confirm that superparasitism may affect the fitness of both the adult female wasp and her progeny, and should therefore be incorporated into models of superparasitism as an adaptive foraging strategy.

     

Regulatory processes and population cyclicity in laboratory populations ofAnagasta Kühniella (Zeller) (Lepidoptera: Phycitidae). III. The development of population models

1. Life table data for interactions between Anagasta kühniella and its ichneumon parasite Venturia canescens in two room ecosystems (A & B) have been analyzed in an attempt to explain and model each room situation. The life table data have been presented in the form of a graphical key-factor analysis, and have been further analyzed by an investigation of the density relationships between the different mortalities and the Angasta densities upon which the mortalities act.
2. In room A (1.2 gm food per container), the parasites were present throughout the interaction. Egg and early larval mortality (k₁) appeared to be directly density-dependent and was the sole stabilizing influence when introduced into the model for room A. The area of discovery of the parasite was relatively constant and its mean value was used to calculate parasitism (k₃) in the model. All other mortalities were density-independent and treated as being constant at their mean values. The model predicts a series of oscillations of decreasing amplitude which are somewhat similar to those observed in the Anagasta population during the early stages of the interaction. The observed mean densities of host and parasite were very close to those predicted.
3. In room B, the parasites were absent for the first 8 generations (1- 2gm food per container). Model B₁ covers this period and includes a direct density-dependent component describing changes in k₁, the remaining mortalities being constant. The observed mean densities approximate to the calculated densities. The parasites were present from the ninth generation and after the eleventh generation the food per container was increased to 7.2 gm. Model B₂ covers the period in room B from generation 11. The most important component of k₁ after the parasites were established is a delayed density-dependent one which appeared to be due to wounding of very small larvae by the probing activities of the parasites. Since the changes in k₁ could not be suitably predicted, the observed values were used in model B₂. This delayed component was not detected in room A due to the relatively small range of parasite densities in room A compared with the 600-fold change in densities in room B. The calculated area of discovery for the parasite population in each generation was found to vary inversely with searching parasite density, and this ‘interference relationship’ was used in the submodel for parasitism. Again, this relationship was not detected in room A due to the much smaller range of parasite densities there. Model B₂ gives oscillations in host and parasite populations arising from parasitism being a delayed density-dependent mortality. The correspondence with the observed oscillations is partly due to the actual k₁-values being used and partly because the submodel for parasitism adequately describes the observed changes in k₃. The tendency for these oscillations to decrease in amplitude is due to both the damping effect of parasite interference and the direct density-dependent component of k₁.

     

Relationships between larval density, adult size and egg production in the cowpea seed beetle, Callosobruchus maculatus

ABSTRACT.

• 1 The eggs of the cowpea seed bettle Callosobruchus maculatus (Fab.) are attached to cowpeas. On hatching, the larvae penetrate the testa and remain in the seed until development is complete and adult eclosion has occurred. The adults do not need to feed and were not allowed to do so.
• 2 Strains from Brazil and Nigeria can produce more than twelve adults from a seed bearing numerous eggs, whereas a strain from the Yemen Republic rarely produced more than three.
• 3 In all three strains the mean weight of the adults produced from a single cowpea declined with increasing initial larval density in the seed.
• 4 Egg production by females is positively correlated with their weight at the time of mating, shortly after emergence.
• 5 Lifetime egg production by females of the Brazilian and Nigerian strains was lower if they came from cowpeas with higher initial larval densities. No such relationship could be demonstrated in the Yemen strain.
• 6 The fecundity of one generation of these beetles, at least in some geographical strains, is significantly affected by the number of larvae entering the hosts in which the adults of that generation have developed.

     

The area of discovery and searching strategy of a primary parasite and two hyperparasites

• 1 Two hyperparasites, Cheiloneurus paralia (Walker) and Marietta exitiosa Compere, of Microterys flavus (Howard), a primary parasite of the brown soft scale Coccus hesperidum L. have been studied.
• 2 The area of discovery of the hyperparasites for secondary hosts (scale insects) is greater than that of the primary parasite, indicating higher searching efficiency of the secondary parasites.
• 3 Cheiloneurus has a higher searching efficiency measured as its area of discovery for discovering both the secondary (scale insect) and the primary (Microterys) hosts, as compared with Marietta.
• 4 The searching efficiency of Cheiloneurus increased in the presence of its own males.
• 5 In each species there is a non-linear relationship between the searching efficiency and female density.
• 6 Cheiloneurus and Marietta present two differing searching strategies. Cheiloneurus tends to exploit as many primary hosts as possible in each secondary host encountered, whereas Marietta, tends to disperse its progeny more regularly by avoiding, to a certain extent, the exploitation of more than one host in each scale insect encountered.

     

Effect of population density on reproduction of two sympatric dung beetle species,Aphodius haroldianus andA. Elegans (Coleoptera: Scarabaeidae)

The effect of population density on reproduction as well as the oviposition modes of two sympatric dung beetle species, Aphodius haroldianus (a low fecundity/high parental effort species) and A. elegans (a high fecundity/low parental effort species) was studied at a pasture in central Japan from 1982 to 1986.

1. The adult population density of A. haroldianus was high (>40 per dung pat). The density of A. elegans was low (<5 per dung pat). Oviposition of A. haroldianus was suppressed above the density of about 10 adults of conspecifics but not affected by the density of other species. The intra- and interspecific density effects on oviposition were not detected in A. elegans.
2. The number of A. haroldianus adults per pat decreased with dung age, while that of A. elegans increased until sixth day after deposition and then decreased. The number of eggs laid per pat was not different between 1-day-and 3-day-old pats for A. haroldianus. However, more eggs of A. elegans were found in 3-day-old pats than in 1-day-old ones.
3. In the both species, the amplitude of population fluctuations was not remarkable; the maximum/minimum ratio for five years being 2.3 for A. haroldianus and 2.9 for A. elegans. Different density dependent processes were suggested to function for the small fluctuation of population density between the two species, i.e. intraspecific density effect on oviposition for A. haroldianus and contest type competition for food among larvae of A. elegans.