Does fecundity drive the evolution of insect diet?

We investigate whether egg load (a surrogate for fecundity) drives host specificity in a herbivorous insect. In many insects, including our study organism (Edith's checkerspot butterfly), both egg load and tendency to accept low-ranked hosts increase during each search for an oviposition site. Effects on host acceptance of egg load and passage of time are thereby potentially confounded. We conducted two experiments designed to disentangle these effects. In both experiments, we estimated the times of first acceptance of both a high-ranked and a low-ranked host, without allowing the insects to oviposit. In the first experiment, we measured egg load at the time of first acceptance of the low-ranked host. The later the time of first acceptance, the higher was the fecundity. We therefore reject the hypothesis that all insects accepted the low-ranked host at the same predetermined egg load. In the second experiment, we measured egg load 48 h after the high-ranked host was first accepted. We found no relationship between egg load and timing of acceptance of the low-ranked host. Insects with higher rates of egg accumulation did not accept the low-ranked host sooner. Taken together, these results suggest that acceptance of the low-ranked host is not driven directly by egg load. Rather, this acceptance results from some other process that is influenced by time since last oviposition. We conclude that there is no evidence to support the assumption that females with high rates of egg accumulation are more likely to accept low-ranked hosts.     

Effects of pre-adult and adult experience on host acceptance in choice and non-choice tests in two strains ofTrichogramma

The effect of adult learning through an oviposition experience, and pre-adult learning through development inside a host was investigated in two strains of an Australian egg parasitoid,Trichogramma nrivelae (Hymenoptera: Trichogrammatidae). Host response was measured in two types of laboratory preference tests. In single host tests, females reared on three lepidopteran hosts (Heliothis punctigera (Noctuidae),Papilio aegeus (Papilionidae), andHypolimnas bolina (Nymphalinae)) were presented host eggs individually, and allowed two ovipositions. Pre-adult experience affected host preference in only one strain, while acceptance of a host was increased in both strains when they had previously oviposited in this host species. An oviposition experience had a stronger effect on host preference than pre-adult experience. In choice tests, pairwise combinations of hosts were arranged in an alternating grid. The ratio of host acceptances to host contacts was computed for the whole test and up to the first oviposition. These indicated that effects of rearing host were weak or absent, but the host chosen initially had a strong effect on host preference. Relative size of the hosts had a strong effect on choice of the first host. The implications of learning inTrichogramma are discussed in relation to host preference testing procedures and the selection of candidate strains for mass rearing and inundative release.     

Population differences in host use by a seed-beetle: local adaptation, phenotypic plasticity and maternal effects

For insects that develop inside discrete hosts, both host size and host quality constrain offspring growth, influencing the evolution of body size and life history traits. Using a two-generation common garden experiment, we quantified the contribution of maternal and rearing hosts to differences in growth and life history traits between populations of the seed-feeding beetle Stator limbatus that use a large-seeded host, Acacia greggii, and a small-seeded host, Pseudosamanea guachapele. Populations differed genetically for all traits when beetles were raised in a common garden. Contrary to expectations from the local adaptation hypothesis, beetles from all populations were larger, developed faster and had higher survivorship when reared on seeds of A. greggii (the larger host), irrespective of their native host. We observed two host plant-mediated maternal effects: offspring matured sooner, regardless of their rearing host, when their mothers were reared on P. guachapele (this was not caused by an effect of rearing host on egg size), and females laid larger eggs on P. guachapele. This is the first study to document plasticity by S. limbatus in response to P. guachapele, suggesting that plasticity is an ancestral trait in S. limbatus that likely plays an important role in diet expansion. Although differences between populations in growth and life history traits are likely adaptations to their host plants, host-associated maternal effects, partly mediated by maternal egg size plasticity, influence growth and life history traits and likely play an important role in the evolution of the breadth of S. limbatus’ diet. More generally, phenotypic plasticity mediates the fitness consequences of using novel hosts, likely facilitating colonization of new hosts, but also buffering herbivores from selection post-colonization. Plasticity in response to novel versus normal hosts varied among our study populations such that disentangling the historical role of plasticity in mediating diet evolution requires the consideration of evolutionary history.     

Superparasitism in the solitary ectoparasitoid Aptesis nigrocincta: the influence of egg load and host encounter rate

Theory predicts that the acceptance of hosts already parasitized by a conspecific will depend both on egg load and the availability of hosts. In the present laboratory study, we tested the effect of egg load and host encounter rate on the propensity of superparasitism in the solitary parasitoid Aptesis nigrocincta Gravenhorst (Hymenoptera, Ichneumonidae), a synovigeneous ectoparasitoid of prepupae of the European Apple Sawfly. Parasitoid females carry few voluminous eggs at a time and the egg maturation rate is less than one egg per day. Egg load was manipulated by giving females access to hosts one week prior to the start of treatments and host availability by giving females access to either one host cocoon every day or every other day. In the first treatment where females had a high egg load of 5.3 egg in their ovaries and encountered host cocoons at low rates, we found that parasitized hosts were accepted to the same degree as healthy hosts. In females with significantly decreased egg load (3.8 eggs) encountering hosts at the same rate we found a slight but non-significant decrease in the acceptance of parasitized hosts compared with healthy hosts. In contrast, A. nigrocincta females accepted significantly fewer parasitized hosts at a high host encounter rate that would lead them to the point of egg limitation in the near future. Within the range of egg loads tested, the host encounter rate appears to be the most important determinant for a females decision to oviposit onto hosts already parasitized by a conspecific.     

Superparasitism in the solitary ectoparasitoid Aptesis nigrocincta: the influence of egg load and host encounter rate

Theory predicts that the acceptance of hosts already parasitized by a conspecific will depend both on egg load and the availability of hosts. In the present laboratory study, we tested the effect of egg load and host encounter rate on the propensity of superparasitism in the solitary parasitoid Aptesis nigrocincta Gravenhorst (Hymenoptera, Ichneumonidae), a synovigeneous ectoparasitoid of prepupae of the European Apple Sawfly. Parasitoid females carry few voluminous eggs at a time and the egg maturation rate is less than one egg per day. Egg load was manipulated by giving females access to hosts one week prior to the start of treatments and host availability by giving females access to either one host cocoon every day or every other day. In the first treatment where females had a high egg load of 5.3 egg in their ovaries and encountered host cocoons at low rates, we found that parasitized hosts were accepted to the same degree as healthy hosts. In females with significantly decreased egg load (3.8 eggs) encountering hosts at the same rate we found a slight but non‐significant decrease in the acceptance of parasitized hosts compared with healthy hosts. In contrast, A. nigrocincta females accepted significantly fewer parasitized hosts at a high host encounter rate that would lead them to the point of egg limitation in the near future. Within the range of egg loads tested, the host encounter rate appears to be the most important determinant for a females decision to oviposit onto hosts already parasitized by a conspecific.     

Multifaceted determinants of host specificity in an aphid parasitoid

The host specificity of insect parasitoids and herbivores is thought to be shaped by a suite of traits that mediate host acceptance and host suitability. We conducted laboratory experiments to identify mechanisms shaping the host specificity of the aphid parasitoid Binodoxys communis. Twenty species of aphids were exposed to B. communis females in microcosms, and detailed observations and rearing studies of 15 of these species were done to determine whether patterns of host use resulted from variation in factors such as host acceptance or variation in host suitability. Six species of aphids exposed to B. communis showed no signs of parasitism. Four of these species were not recognized as hosts and two effectively defended themselves from attack by B. communis. Other aphid species into which parasitoids laid eggs had low suitability as hosts. Parasitoid mortality occurred in the egg or early larval stages for some of these hosts but for others it occurred in late larval stages. Two hypotheses explaining low suitability were investigated in separate experiments: the presence of endosymbiotic bacteria conferring resistance to parasitoids, and aphids feeding on toxic plants. An association between resistance and endosymbiont infection was found in one species (Aphis craccivora), and evidence for the toxic plant hypothesis was found for the milkweed aphids Aphis asclepiadis and Aphis nerii. This research highlights the multifaceted nature of factors determining host specificity in parasitoids.     

Visual and Chemical Cues Used in Host Location and Acceptance by a Dipteran Parasitoid

Locating potential hosts for egg laying is a critical challenge in the life history of many insects. Female insects in several orders have evolved mechanisms to find hosts by using olfactory and visual signals derived from their hosts. We describe visual and chemical cues used by the dipteran parasitoid Apocephalus paraponerae (Diptera: Phoridae) in the location and acceptance of its host ant Paraponera clavata (Hymenoptera: Formicidae: Ponerinae). Our results show that A. paraponerae uses the visual cue of ant body size when locating hosts at short range and that these flies lay more eggs in ants that retain their surface chemicals than in ants with these chemicals removed. We compare the cues used by A. paraponerae with cues used by tephritid fruit flies in location and acceptance of their hosts, and we suggest further avenues for the study of host location, acceptance, and host discrimination of A. paraponerae and other parasitoids of ants.     

Comparison of Foraging Behavior, Interspecific Host Discrimination, and Competition of Encarsia formosa and Amitus fuscipennis

The foraging behavior of Amitus fuscipennis MacGown & Nebeker and Encarsia formosa Gahan was studied on tomato leaflets with 20 Trialeurodes vaporariorum (Westwood) larvae in the first or third stage. Ten of the whitefly larvae were previously parasitized and contained a conspecific or a heterospecific parasitoid egg or larva. The host type (host stage and/or previous parasitization) did not influence the foraging behavior of either parasitoid species. The residence time on these tomato leaflets was about 0.9 h for A. fuscipennis and 1.9 h for E. formosa. Amitus fuscipennis hardly stood still and fed little, while E. formosa showed extensive standing still and feeding. As a result, the time walking while drumming was similar for both parasitoid species. The numbers of host encounters and ovipositions per leaflet were similar for both parasitoid species. However, the residence time of A. fuscipennis was half as long as that of E. formosa so the rate of encounters and ovipositions was higher for A. fuscipennis. Amitus fuscipennis is more efficient in finding and parasitizing hosts under these conditions. The walking activity and host acceptance of the synovigenic E. formosa diminished with the number of ovipositions, but not those of the proovigenic A. fuscipennis. Encarsia formosa is egg limited, while A. fuscipennis is time limited because of its short life span and high egg load. Both parasitoid species discriminated well between unparasitized larvae and self-parasitized larvae, but discriminated poorly those larvae parasitized by a conspecific and did not discriminate larvae parasitized by a heterospecific. Self-superparasitism, conspecific superparasitism, and multiparasitism were observed for both parasitoid species. Superparasitism always resulted in the emergence of one parasitoid and multiparasitism resulted in a higher emergence of one parasitoid of the species that had parasitized first. The data suggest that A. fuscipennis is a good candidate for use in biological control of high-density spots of T. vaporariorum when we consider its high encounter and oviposition rate.     

Effect of larval host food substrate on egg load dynamics, egg size and adult female size in four species of braconid fruit fly (Diptera: Tephritidae) parasitoids

Life history theory predicts that individuals will allocate resources to different traits so as to maximize overall fitness. Because conditions experienced during early development can have strong downstream effects on adult phenotype and fitness, we investigated how four species of synovigenic, larval-pupal parasitoids that vary sharply in their degree of specialization (niche breadth) and life history (Diachasmimorpha longicaudata, Doryctobracon crawfordi, Opius hirtus and Utetes anastrephae), allocate resources acquired during the larval stage towards adult reproduction. Parasitoid larvae developed in a single host species reared on four different substrates that differed in quality. We measured parasitoid egg load at the moment of emergence and at 24 h, egg numbers over time, egg size, and also adult size. We predicted that across species the most specialized would have a lower capacity to respond to changes in host substrate quality than wasps with a broad host range, and that within species, females that emerged from hosts that developed in better quality substrates would have the most resources to invest in reproduction. Consistent with our predictions, the more specialized parasitoids were less plastic in some responses to host diet than the more generalist. However, patterns of egg load and size were variable across species. In general, there was a remarkable degree of reproductive effort-allocation constancy within parasitoid species. This may reflect more “time-limited” rather than “egg-limited” foraging strategies where the most expensive component of reproductive success is to locate and handle patchily-distributed and fruit-sequestered hosts. If so, egg costs, independent of degree of specialization, are relatively trivial and sufficient resources are available in fly larvae stemming from all of the substrates tested.     

Innate and Learned Cues: Scale Cover Selection by Aphytis melinus (Hymenoptera: Aphelinidae)

Aphytis melinus recognizes and accepts covers of its host, California red scale, Aonidiella aurantii (Maskell) (Homoptera: Diaspididae), before assessing the size or quality of the scale body beneath. We evaluated the role of a non-volatile kairomone, O-caffeoyltyrosine, and prior experience with hosts on the recognition (antennal drumming) and acceptance (ovipositor probing) of scale covers differing in age and, therefore, size. We tested several hypotheses concerning the role of experience with hosts on host recognition and acceptance. The first predicts that experience with a particular host size leads to increased selection of that host size in the future. The second predicts that the quality of the experience with hosts sets a threshold of quality for future acceptance. We manipulated the quality of wasp experience with hosts by exposing some wasps to high-quality hosts (large scale insects under large covers) and other wasps to low-quality hosts (small scale insects under small covers and small scale insects under large covers). Control (naive) wasps were held without experience with hosts. Wasps were then offered five size classes of covers directly after removal from the scale insects (unmanipulated) or after removing the kairomone from the covers (kairomone-free). For covers with natural levels of kairomone, no effect of experience with hosts on host recognition was observed. When the kairomone was removed, however, any experience with hosts increased recognition compared to naive wasps. Moreover, experienced wasps preferentially recognized covers of the size to which they had experience. Results for host acceptance differed from those for host recognition. Wasps given experience with large hosts accepted more covers with kairomone than wasps in other treatments, but the size preference did not vary among treatments. When the kairomone was removed, however, wasps given experience with large hosts under large covers preferred larger covers. Host recognition and acceptance are controlled by different behavioral mechanisms. Prior experience with hosts does not alter host recognition but does affect the rate of acceptance. The quality of the experience does not affect the acceptance of covers containing natural levels of kairomone but does affect host acceptance when the kairomone is removed. Experience with hosts alters the motivation of wasps to accept covers, and the direction of this effect is determined by the size (quality) of body the wasps were given during the experience.     

Functional response and egg distribution among hosts by Pseudapanteles dignus,a larval endoparasitoid of Tuta absoluta

The functional response of a biocontrol agent has been classically pointed out as a quantitative evaluation criterion to understand its killing capacity to an arthropod pest. In this paper, we revisited the functional response of the internal larval parasitoid Pseudapanteles dignus (Muesebeck) (Hymenoptera: Braconidae), a candidate for biocontrol of the South American tomato leafminer, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), measured as the daily egg oviposition of single parasitoid females at increasing densities of T. absoluta larvae through dissection of hosts. The functional response curve of the number of parasitized hosts was fitted out taking into account the number of eggs laid and their distribution among hosts at each T. absoluta larval density. The data also allowed us to discuss the self-superparasitism strategy of this parasitoid as an adaptive trait. Pseudapanteles dignus showed a sigmoid shape functional response and a contagious distribution of eggs among hosts, favouring self-superparasitism and laying a similar number of eggs in each superparasitized host at each T. absoluta density. This research is firstly intended to ascertain about the oviposition behaviour of P. dignus and additionally to provide information on its reproduction to be applied in mass rearing procedures and augmentative releases against T. absoluta.     

Influence of initial egg density and host size on the development of the gregarious parasitoid <Emphasis Type="Italic">Bracon hebetor</Emphasis> on three different host species

Bracon hebetor (Say) (Hymenoptera : Braconidae) is a gregarious parasitoid that attacks a variety of important lepidopterous pests of stored product and in the field. In this study the effect of host species, size and larval competition on parasitoid size, survival and development were investigated. In laboratory studies, wasp eggs at a range of densities, were placed on larvae of different weight of three Lepidoptera host species namely Adoxophyes orana (Fischer von Röslerstamm, Tortricidae), Plodia interpunctella (Hubner, Pyralidae) and, Lobesia botrana(Dennis & Schiffermueller, Tortricidae). On A. orana survival of immature parasitoids was very low at all densities and different host weights. On L. botrana survival progressively reduced as egg density increased at both host weights examined for this host. Survival on P. interpunctella was significantly affected by egg density but not by host weight. Initial egg density had a significant effect on the size of emerging adults from each rearing host. Smaller adult parasitoids emerged as egg density per larva increased. Larval host weight of P. interpunctella and A. orana had a significant effect on the size of emerging adult parasitoids mainly at the higher egg densities used in these experiments. The above results of host quality on fitness of parasitoid are discussed.     

Influence of host age and host deprivation on longevity, egg load dynamics and oviposition rate in Microplitis rufiventris

Adult size, longevity, egg load dynamics and oviposition ofMicroplitis rufiventris Kok. which began their development in the first, second, third （preferred hosts） or fourth （non-preferred hosts） instar larvae of Spodoptera littoralis （Boisd.） were studied. The parasitoid size was largely determined by the initial host size at parasitism. Non-ovipositing females derived from older hosts lived for longer periods than those derived from younger ones. However, the ovipositing females, irrespective of their size, lived for almost the same periods. At emergence, the oviducts of adult females contain a significant amount of mature eggs available for oviposition for a few hours on eclosion day. Egg load increases during the early phase of adult life. The amount of additional mature eggs and rate of egg maturation per hour was greater for wasps derived from preferred hosts compared with those in females derived from non-preferred hosts. The pattern of egg production in M. rufiventris females depended on the availability of hosts for parasitization. Host-deprived females depleted the egg complement with aging; the longer the host deprivation, the lower the oviduct egg load. Marked reduction in both realized or potential fecundity of host-deprived females was observed following host availability. Host privation for more than 3 days induced a marked deficit fecundity pattern through the female＇ s life. The realized fecundity was determined by the interaction among host availability, the number of eggs that are matured over the female＇ s life span, oviposition rate and host size from which the female was derived. These results suggest that： （i） M. rufiventris wasp is a weak synovigenic species; （ii） the maturation of additional eggs is inhibited once the maximum oviduct egg load is reached; （iii） the egg load of the newly emerged female is significantly less than the realized fecundity; and （iv） because M. rufiventris females oviposit fewer eggs when they begin depleting their egg supply at 3 days, augmentative releases will require release immediately following emergence to ensure the highest parasitization rate in the field.     

Influence of egg load and host size on host-feeding behaviour of the parasitoid Aphytis lingnanensis

Abstract.

• 1 Direct behavioural assays were used to investigate the influences of host size and parasitoid egg load on the decision to host feed versus oviposit made by the parasitoid Aphytis lingnanensis Compere. Egg load was manipulated without concurrent influences on the history of host contact by exploiting size-related variation in fecundity and by holding parasitoids at different temperatures to vary the rate of oocyte maturation.
• 2 Host feeding comprised a series of feeding bouts, separated by renewed probing of the scale insect body. Successive feeding bouts were progressively shorter, suggesting that hosts represent ‘patches’ yielding resources at a decelerating rate.
• 3 Parasitoids were significantly more likely to host feed on smaller hosts and oviposit on larger hosts.
• 4 Neither egg load nor the treatment variables (parasitoid size and holding temperature) exerted significant influences on the decision to host feed versus oviposit on second instar (low quality) hosts.
• 5 The failure to observe an effect of egg load on host-feeding decisions was not simply a reflection of the parasitoids being entirely insensitive to egg load; significant effects of egg load on parasitoid search intensity and clutch size decisions were observed.
• 6 Parasitoids developing on second instar (low quality) hosts experienced high levels of mortality late during development and yielded very small adults.
• 7 The discord between these experimental results and predictions regarding the importance of egg load underscores the need for additional work on the proximate basis for host-feeding decisions and the nutritional ecology of insect parasitoids.

     

Determinants of egg load in the soybean aphid parasitoid Binodoxys communis

We used a series of laboratory studies to investigate factors contributing to variability in egg load of the parasitoid Binodoxys communis (Gahan) (Hymenoptera: Braconidae), a biological control agent of the soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae). The change in egg load in newly emerged females over time was determined in response to three treatments: post‐eclosion temperature, sugar meals, and host density. Binodoxys communis females emerge with an average egg load of approximately 40 mature eggs that increases to approximately 200 eggs within 24 h of emergence. The egg maturation rate over this time period is higher when females are held at 26 °C than at 18 °C. And although the egg load of sugar‐fed females was slightly higher than that of starved females, this difference was not statistically significant. Binodoxys communis females that were held with 150 hosts for 8 h laid more eggs than those that were held with 30 hosts, and they also matured more eggs over the subsequent 16 h than those held with 30 hosts or no hosts at all. However, we detected no difference in the egg maturation pattern between B. communis females held with the low host density and that of control females held with no hosts at all. Thus, we conclude that enhanced egg maturation in the higher host‐density treatment is more likely explained by a rapid replenishing of partially depleted ovaries than a host‐induced stimulus of egg maturation per se. Taken together, these results suggest a strategy of maintaining a high egg load and thus avoiding or mitigating the negative effects of egg limitation.     

繁育寄主对三种赤眼蜂个体大小及抱卵量的影响

【目的】繁育寄主及成蜂日龄均会影响赤眼蜂体内的抱卵量,为了解繁育寄主及育出赤眼蜂个体大小与赤眼蜂抱卵量的关系,我们在室内研究了米蛾 Corcyra cephalonica（Stainton）卵和亚洲玉米螟 Ostrinia furnacalis （Güenée）卵作为繁育寄主对3种赤眼蜂雌蜂大小、抱卵量的影响。【方法】在光周期14L:10D、温度25±1℃的室内条件下,以米蛾卵、亚洲玉米螟卵作为繁育寄主,解剖不同日龄（羽化后12-72 h）松毛虫赤眼蜂 Trichogramma dendrolimi Matsumura、玉米螟赤眼蜂Trichogramma ostriniae Pang et Chen以及稻螟赤眼蜂Trichogramma japonicum Ashmead,观察雌蜂抱卵量,测量成蜂的大小,分析雌蜂抱卵量与其日龄、个体大小以及繁育寄主的关系【结果】在羽化后48 h以内,3种蜂的抱卵量随雌蜂日龄的增长而增加。羽化后72 h,除米蛾卵繁育的玉米螟赤眼蜂及玉米螟卵繁育的松毛虫赤眼蜂的抱卵量比羽化后48 h时略高外,其他组合均出现下降。以亚洲玉米螟卵为繁育寄主时的玉米螟赤眼蜂的抱卵量显著高于对应日龄的以米蛾卵为繁育寄主时的抱卵量,而松毛虫赤眼蜂（除羽化后12和24 h外）和稻螟赤眼蜂则相反;以米蛾卵为繁育寄主时,相同日龄的赤眼蜂中,松毛虫赤眼蜂抱卵量最高,稻螟赤眼蜂的抱卵量最低;以亚洲玉米螟卵为繁育寄主时,玉米螟赤眼蜂抱卵量最高,稻螟赤眼蜂抱卵量最低。雌蜂抱卵量与雌蜂个体大小呈线性正相关,相关程度随雌蜂日龄增加而更加明显。【结论】后足胫节长度可以作为评价松毛虫赤眼蜂、玉米螟赤眼蜂和稻螟赤眼蜂质量的指标。赤眼蜂抱卵量受繁育寄主、赤眼蜂蜂种及雌蜂日龄的显著影响,寄主的适合性也会影响育出赤眼蜂的大小,筛选合适的繁育寄主有助于提高赤眼蜂的质量。     

Body size affects host defensive behavior and progeny fitness in a parasitoid wasp,Lysiphlebus fabarum

This study tested effects of maternal body size on foraging behavior and progeny development in a thelytokous population of Lysiphlebus fabarum (Marshall) (Hymenoptera: Braconidae). Small and large wasps were reared from first and second instar hosts [black bean aphid, Aphis fabae Scopoli (Hemiptera: Aphididae)], respectively, and each was provided with a patch (bean leaf disk) containing either 15 small (second instar) or 15 large (fourth instar) hosts for a 30‐min foraging period. Neither body size nor host size affected time allocation to various behaviors within a patch, but second instar aphids produced significantly more mummies than fourth instars. The preferred attack orientation was from the side of the aphid, suggesting wasps were sensitive to the risk of smearing with cornicle secretions. Few wasps developed in fourth instar hosts, suggesting later host instars were somewhat resistant to parasitism. Second instar hosts, the most suitable stage for L. fabarum development, relied more on defensive behavior, specifically kicking and secreting cornicle droplets. Large wasps were more likely to elicit a double cornicle secretion, indicating that aphids graded their response to the size of the attacker. Larger wasps were also more likely to be smeared with cornicle secretion, suggesting they were more vulnerable than small wasps. Although small wasps had smaller eggs than large wasps, there was no effect of maternal egg size on the size of progeny. However, daughters of small females emerged with larger egg loads than daughters of large mothers, and their eggs tended to be slightly smaller, although not significantly. Regression analysis revealed a positive correlation between maternal egg size and progeny developmental time for small and large wasps, and between maternal egg size and progeny egg load for small wasps. These results confirm maternal effects of body size in an aphid parasitoid, and reveal that vulnerability to host behavioral defenses is also body size dependent.     

Egg load of lab-cultured <Emphasis Type="Italic">Anaphes iole</Emphasis> and effects of mate presence and exposure time on load depletion

Anaphes iole Girault (Hymenoptera: Mymaridae) is a solitary egg parasitoid of Lygus bugs (Heteroptera: Miridae) in North America. This research considered factors that might impact the egg load of lab-cultured A .iole females, reared from Lygus hesperus Knight egg patches. The following hypotheses were tested: (1) egg load was related to body size and not affected by female age, and (2) egg load depletion was not affected by mate presence and time (in days) that females were exposed to host patches. Initial egg load averaged 48 mature eggs and no immature eggs were detected in the ovarioles of dissected females. Egg load was neither related to body size (hind tibia or forewing length) nor affected significantly by age (0, 1 or 2days old honey-fed females). Mate presence (females with or without males) and exposure time (1, 3 or 5days on the same host patch) had no effect on egg load depletion. Females usually depleted most of their egg load within 24h. From 86 to 92% of females contained less than six mature eggs and no immature eggs after 1, 3 or 5days of exposure to host patches. The results of this study suggest that A. iole females are certainly pro-ovigenic and initial egg load does not correlate with body size or age. Since mated and unmated females deplete most of their egg load in 24h, time-efficient production of progeny may result when ovipositing parasitoids are exposed to suitable hosts for just a few days.The United States Government has the right to retain a non-exclusive, royalty-free license in and to any copyright of this article. This article reports the results of research only. Mention of a commercial or proprietary product does not constitute an endorsement of the product by the United States Department of Agriculture.     

The effect of host size on the sex ratio of Syngaster lepidus, a parasitoid of Eucalyptus longhorned borers (Phoracantha spp.)

The solitary larval ectoparasitoid, Syngaster lepidus Brullé, parasitizes the cryptic larvae of two wood-boring beetles, Phoracantha recurva Newman and Phoracantha semipunctata F. The objective of this study was to determine how the female parasitoids allocated the sex of progeny when presented with larval hosts of uniform size classes. Host size was directly correlated with age of the Phoracantha larval hosts. Groups of Phoracantha larvae of a single age class (2-, 3-, 4-, or 5-week-old) were exposed to parasitoids, and sex ratios of the resulting parasitoid progeny from each host age class were determined. A significant relationship was observed among the sizes of P. recurva and P. semipunctata hosts and the sex ratio of emerging parasitoids. Parasitized 2-week-old beetle larvae of both Phoracantha spp. produced only male S. lepidus progeny, whereas older larval hosts produced increasing proportions of female parasitoids (up to 80% females from 5-week-old hosts). Two-week-old Phoracantha larvae of both species produced fewer parasitoids than host larvae 3–5-week-old. The size of parasitoid progeny consistently increased with host larval age (size), and female parasitoids were larger than males across all host size classes. Male S. lepidus developed in approximately 25 days from 2-week-old hosts, and 19–21 days in 3–5-week-old hosts. Female S. lepidus developed in 22–25 days, with developmental time increasing with host size.     

Egg Load and Body Size of Lab-cultured Cotesia marginiventris

The egg load of lab-cultured Cotesia marginiventris (Cresson) (Hymenoptera: Braconidae), a solitary koinobiont endoparasitoid of noctuid caterpillars, was determined in this study. Information on egg load may provide clues to more efficient in vivo rearing of C. marginiventris. I tested the hypothesis that egg load, defined as the number of mature oöcytes (i.e., fully chorionated eggs) found in adult females, was related to body size. Cotesia marginiventris females possessed two ovaries and two ovarioles per ovary; mature eggs were found in ovaries and oviducts. Newly-emerged females held an average of 149 mature eggs. Immature eggs were slightly visible in the distal portions of the ovarioles; they were not counted. Egg load was marginally related to body size (i.e., hind tibia length). The results of this study suggest that (1) body size can sometimes predict egg load or potential fecundity of lab-cultured C. marginiventris and (2) an efficient rearing system that exploits the potential fecundity of C. marginiventris might involve using young females and allowing them to oviposit in new hosts, each day, for up to a week.