Host Egg Size Research Articles

Reproductive ecology and egg parasitism of the Samoan swallowtail butterfly

AbstractWe investigated the reproductive ecology and effects of egg parasitism on the Samoan swallowtail butterfly (Papilio godeffroyi), which survives only on Tutuila Island, American Samoa, after having disappeared from the much larger islands of Upolu and Savai‘i in independent Samoa. During monthly surveys of its only known host plant, Micromelum minutum, across eight sites in 2013 and 2014, we collected eggs, eggshells, larvae, pupae, and pupal exuviae. Live specimens were reared under laboratory conditions to determine reproductive outcomes, developmental rates, and sex ratios, as well as parasitoid attack frequencies, brood sizes, and sex ratios. Sixty‐six of 448 (14.7%) eggs produced larvae, 47 of which became adults. The sex ratio was approximately even overall and within each developmental stage. Eggs were slightly larger on individual host trees and in host tree stands that yielded more eggs per unit of foliage, indicating that ovipositing females responded to some features of host trees and stands. Eggs hatching female or male larvae were similar in size, and the sexes developed at similar rates. A newly described species of parasitoid wasp, Ooencyrtus pitosina (Encyrtidae), emerged from 73.6% of 382 butterfly eggs that failed to hatch in the laboratory (62.7% of 448 eggs overall). Forty‐one other eggs contained dead parasitoid larvae. An additional, unidentified Ooencyrtus wasp species emerged from a single P. godeffroyi egg. No parasitoids were reared from P. godeffroyi larvae or pupae. Of 656 P. godeffroyi eggshells collected in the field and examined in the laboratory, 62.2% showed signs of having been parasitized by O. pitosina. There was no evidence that parasitism rates were density‐dependent. O. pitosina brood sizes ranged from 1 to 5, with the sex ratio skewed toward females (2.40 F:1.00 M). Larger parasitoid broods were associated with slightly larger host eggs, indicating that female wasps may adjust brood size according to host egg size or that fewer wasp larvae are able to complete development in smaller eggs. Techniques used to rear both P. godeffroyi and O. pitosina in the laboratory could be applied to a captive‐rear, wild‐release program, which may facilitate reestablishment of the species in Samoa.

Variation in parasitoid adult size is related to host egg size, maternal state and developmental time

AbstractBody size is a characteristic of many animal species that is correlated with many fitness‐related traits. Parasitoids are important biological control agents of pests; larger parasitoids often have greater fitness and enhanced performance. Host size is a major influence on parasitoid size, which has been explored in the important egg parasitoid Anastatus disparis (Hymenoptera: Eupelmidae), a potential biological control agent for several Lepidopteran pests. Here, we found that the body size of A. disparis females increased with increasing host egg size, while host egg size did not significantly affect male size. In addition, both female and male offspring sizes significantly increased with increasing maternal size, and female offspring produced by younger mothers were also larger. Furthermore, the body sizes of both females and males appeared to increase when the total development time from egg to adult eclosion decreased. Male offspring produced by larger females have shorter development times, while female offspring produced by older females have longer development times. Consequently, our results suggested that the effect of maternal status on offspring size may be mediated by influencing development time. In summary, our results indicated that the body size of A. disparis is determined by multiple factors with differing effects on females and males, and our results provide guidance for its effective mass rearing and its performance in the field.

Egg rejection based on egg size recognition as a specific strategy against parasitic cuckoos.

In the coevolutionary interactions between avian brood parasites and their hosts, egg recognition based on color and/or pattern is a common and effective defense to counter parasitism. However, for egg recognition based on size, only a few studies have found affirmative results, and they do not provide unambiguous evidence that egg size recognition in hosts has evolved as an important and specific anti-parasite adaptation against parasite eggs. We studied the brood parasite system between the Asian emerald cuckoo Chrysococcyx maculatus and its host, the chestnut-crowned warbler Phylloscopus castaniceps. The cuckoo parasitizes the warbler using non-mimetic and larger eggs at a parasitism rate of 12.9%. The warbler nests used in this experiment were built in a dark environment with the nest illuminance near 0 lux. Experiments with 2 types of model eggs with colors and patterns resembling cuckoo eggs of different sizes (cuckoo egg size or host egg size) showed that the warblers were able to reject 63.6% of cuckoo model eggs under these dim light conditions. However, model eggs with the same color and pattern similar to the warbler egg size were always accepted. This study provides strong evidence supporting the theory that egg size recognition can be evolved in hosts as a specific anti-parasite adaptation against cuckoos. We suggest that the egg size recognition of the warbler is an outcome of the tradeoff between the costs of violating the parental investment rule and suffering cuckoo parasitism.

Morphological variation of the parasitic wasp Paracentrobia subflava (Hymenoptera: Trichogrammatidae) emerged from different leafhopper species

The parasitic wasp Paracentrobia subflava (Girault) (Hymenoptera: Trichogrammatidae) develops within the eggs of the corn leafhopper Dalbulus maidis (DeLong) (Hemiptera: Cicadellidae), one of the most important pests in maize throughout the Americas. The aim of the present study was to determine whether variation occurs in female and male body size and male genitalia of P. subflava emerged from eggs of D. maidis and two other host species: Dalbulus elimatus (Ball), and Dalbulus quinquenotatus (DeLong and Nault), representing different species groups within the genus. Body variation of the emerged adult parasitoids was evaluated using traditional morphometrics and male genitalia shape variation was assessed using geometric morphometrics. Female parasitoids emerged from D. elimatus eggs had significantly larger hind tibiae, wings and ovipositor. Most antennal variables also exhibited significant differences in females emerged from D. elimatus. In contrast, little differentiation was found among parasitoid males emerged from the different Dalbulus hosts. Accordingly, shape of male genitalia was similar when P. subflava developed in each of the three Dalbulus host eggs. Egg size differs among the examined Dalbulus species, but does not seem to be associated with patterns of variation in parasitoid size. Implications of this morphological variation for parasitoid identification and its relationship with host egg size and structure are discussed.

Use of time in a decision‐making process by a parasitoid

1. Time perception is seldom studied in invertebrates, with the limited experimental evidence being insufficient to provide a comprehensive pattern of the capacity of invertebrates to measure time and use it in decision‐making processes.2. In this study, it was hypothesized that insect parasitoids have evolved the capacity to measure time precisely and to use it to optimize foraging decisions related to host exploitation. To examine time perception in females of the gregarious egg parasitoid Trichogramma euproctidis, the present study used their ability to adjust their investment (number of eggs laid) in a host to the initial transit duration (interval between the first contact with the host and the following contact with the substrate). Females utilize this method to assess host egg size, as a large egg necessarily requires more time to evaluate than a small host. In this study, the initial transit duration for a given sized egg was artificially extended by suspending it.3. For similar sized hosts, female T. euproctidis significantly increased both oviposition duration and progeny allocation following a longer initial transit duration.4. These results demonstrate the intrinsic capacity of this parasitoid to measure time and to adjust their progeny investment accordingly. This is believed to be one of the few demonstrations of a retrospective measure of time in an invertebrate.

EFFECT OF TEMPERATURE, PHOTOPERIOD, BIOLOGICAL AND CHEMICAL FACTORS OF THREE HOST SPECIES ON THE PERFORMANCE OF THE EGG PARASITOID Trichogramma evanescens WEST.

In order to evaluate the activity of Trichogramma evanescens west due to the effect of temperature, photoperiod egg size, weight, total protein, carbohydrates, and lipids of threehost species Sitotroga cerealella Oliv., Pectinophora gossypiella, Spodoptera littoralis without scales and S. littoralis with scales. The highest percentage of parasitism was obtained in P. gossypiella (66.75%) followed by 57.25, 41.5 and 16.25% in S. cerealella, S. littoralis without scales and S. littoralis with scales, respectively. While, The highest percentage of adult wasps emerged from the parasitized host was occurred in S. cerealella (45%). Results reflected eggs of S. cerealella was more preferredfor T. evanescens wasps than S. littoralis eggs due to larger amount of protein, carbohydrates, lipids and egg weight (13.36, 2.4 and 3.59 mg/gm) respectively. The consequences of these observations led to high percentage of parasitism and adult wasps emergence (57.25 and 45.0%) in case of wasps produced from S. cerealella. Host egg size significantly differed (P= 0.0098) between all tested host eggs. While, no significant difference (P= 0.0956) was recorded for the egg weight between all tested egg host. Effect of light period [light regimes; (A)16:8h L:D, (B)12:12h L:D, (C) 8:16h L:D at 25±1oC and 70±5% RH] on the rate of parasitism and sex ratio of the parasitoid T. evanescens. The highest rate of parasitism (86.75 %) was recorded in the treatment (A), while the lowest rate (77.25%) was found in the treatment (B). Sex ratios in the treatments (A, B and C) were 68.25, 74.25, and 78.5% for Females, respectively. No significant differences was recorded among different photoperiod regimes tested with respect to longevity and life cycle. Positive relationship between temperature and T. evanescens percentage of parasitism and negative relationship between longevity and temperature were recorded.

Tapeworm (Hymenolepis diminuta) infection in flour beetles (Tribolium confusum): does it cause a trade-off between host fecundity and egg size?

Inter- and intra-specific comparisons commonly reveal an inverse relationship between fecundity and offspring size. Many animals also vary egg size in response to environmental conditions. Infection of flour beetles Tribolium confusum Jaquelin Du Val, 1868 with the rat tapeworm Hymenolepis diminuta (Rudolphi, 1819) causes a major reduction in host fecundity. This study tested if this fecundity reduction was associated with changes in host egg size. Age-matched beetles were either fasted and then exposed to parasites, fasted only, or neither, and egg production and egg length determined for 5 weeks postexposure. Control beetles that were neither fasted nor exposed to parasites had steady egg production, but produced smaller eggs as they aged. Beetles that were fasted only, produced fewer but larger eggs for 1–2 weeks after the fast ended. Then, fecundity and egg size returned to control levels. Infected beetles also produced fewer, larger eggs for 1–2 weeks, but at levels indistinguishable from beetles that had been fasted only. After 2 weeks, while fecundity of infected beetles remained low, egg size became similar to noninfected hosts. Beetles appeared to trade-off fecundity and egg size in response to reduced feeding, but not to the presumed nutritional stress of parasitic infection.

Host plant cultivar of the grapevine moth Lobesia botrana affects the life history traits of an egg parasitoid

The quality and susceptibility of insect eggs for egg parasitoids may be affected by the diet experienced by the females that produce the host eggs. We tested the hypothesis that the host plant fed upon by an herbivore during the larval stages will determine the quality of the eggs laid by the adult for an egg parasitoid. We used the tritrophic system comprising five grape cultivars, the European grapevine moth, Lobesia botrana and the parasitoid Trichogramma evanescens. Parasitoid performance in host eggs of different sizes and originating from five grape cultivars was determined. Overall, egg parasitism was higher on cultivars on which L. botrana laid larger eggs, which resulted in higher larval survival and faster development time of the wasps. One exception was found for the cultivar Pinot. Trichogramma wasps parasitized fewer eggs originating from females that fed on the Pinot cultivar as larvae despite good progeny performance (high survival and fast development time). The poor motivation of the parasitoid to oviposit in “Pinot” eggs could be a result of deterrence due to plant compounds ingested by the moth as a larva and transferred to the eggs, or lack of plant-derived compounds that stimulate oviposition in the parasitoid. Interestingly, within a cultivar, Trichogramma larval survivorship was higher in younger, smaller eggs than in older, larger ones. This effect however is confounded by the effect of the plant cultivar, since the host egg size varies among grape varieties. Overall, the results of this study support the hypothesis that an herbivore’s host plant can influence the performance of its egg parasitoids.

Blowfly Infestation at the Nestling Stage Affects Egg Size in the Pied FlycatcherFicedula hypoleuca

The long-term effects on the egg size of breeding females that had suffered parasitism when they were nestlings are described for a wild population of Pied Flycatchers naturally parasitized by the blowfly Protocalliphom azurea larvae, a common nest-dwelling, blood-sucking ectoparasite of cavity-nesting birds in the Mediterranean region. As adults, females reared in blowfly-infested nests laid smaller eggs than their counterparts raised in nests not infested by blowflies. This relationship held irrespective of female size, condition and maternal egg size, and was random with respect to female quality and consistent across a female's lifetime. Except for egg size, no long-term effects on host longevity or other fitness components, such as lifetime reproductive success, were detected. Although the mechanisms causing long-term depression of host egg size remain unknown, the recent discovery that Protocalliphora blowflies transmit viruses to nestlings offers new avenues of research on this issue.

Effect of host quality ofCallosobruchus maculatus(Coleoptera: Bruchidae) on performance of the egg parasitoidUscana lariophaga(Hymenoptera: Trichogrammatidae)

Development and reproductive success of the solitary egg parasitoid Uscana lariophaga Steffan were examined after development in eggs of the bruchid storage pest Callosobruchus maculatus Fabricius reared at either low or high densities on cowpea seeds and laid at day 1 and 4 of maternal life. Both bruchid larval competition and maternal age negatively affected egg size, but the latter more than the former. Uscana lariophaga reared in small hosts developed slower, were smaller and produced fewer eggs compared to parasitoids reared in large hosts. Fecundity of the parasitoid was heavily influenced by host egg size. This was reflected in the values for the intrinsic rate of increase of U. lariophaga, which differed for wasps that developed in host eggs laid by bruchid females of different age. Wasps allocated marginally more female offspring to larger hosts.

REDUCTION OF EGG SIZE IN NATURAL POPULATIONS OF THREESPINE STICKLEBACK INFECTED WITH A CESTODE MACROPARASITE

Manifestations of infectious disease may represent host adaptations to avoid or reduce the effects of infection on host fitness, parasite manipulations that benefit the pathogen's fitness, or nonadaptive side effects of parasitism. Threespine stickleback fish (Gasterosteus aculeatus) from Alaska and the cestode macroparasite Schistocephalus solidus provide an excellent system for study of the effects of parasitism on host egg size because females in populations there are capable of producing clutches of eggs in the face of substantial infection, contrary to the inhibition of reproduction that has been observed in other stickleback populations or other species of fish. A side effect resulting in reduction of mean ovummass among infected females was predicted based on the egg production process in female stickleback, the considerable energy and resource demands of S. solidus, and the chronic and progressive nature of the effects the macroparasite should have on the host fish. In each of 9 populations of G. aculeatus representing replicate natural experiments in lakes scattered across the Matanuska-Susitna Valley and the Kenai Peninsula of south-central Alaska and among all populations combined, the mean ovum mass of infected female fish is significantly reduced in comparison with that of uninfected females taken from the same population at the same time. Reduction in mean female egg mass ranged from 8 to 32% across all populations. To examine whether reduction in mean female ovum mass was a nonadaptive side effect or an adaptation, relatively large data sets from 2 of the populations were used. Mean ovum mass of infected females was predicted to decrease directly in relation to parasite index (PI) if the diminution in mean egg mass were the result of a nonadaptive side effect resulting from host nutrient loss. Alternatively, the absence of a relationship between PI and reduction in ovum mass is predicted if decreases in mean female ovum mass result from host or parasite adaptation (or both) because lightly infected hosts should show a response similar to that of heavily infected ones. In each of the 2 populations, there is a significant, negative relationship between mean female ovum mass and PI, demonstrating a correlation between the decrease in ovum mass and the level of infection. Thus, the results are consistent with the hypothesis that the reductions in mean female egg mass represent side effects of parasitism involving nutrient theft. Moreover, the proportional decline in egg mass with increasing PI apparently differed between the 2 populations, and there was no significant relationship between mean percent decrease in mean female ovum mass and mean PI across populations. These observations suggest that unknown ecological and evolutionary factors influence the degree of reduction in mean ovum mass in a population-specific manner.

Behaviour without function: egg rejection in the absence of parasitism

Avian brood parasites and their hosts provide one of the classical examples of coevolution. One famous aspect of this is the mimicry of host egg size, shape and coloration by some cuckoos. This parasitic tactic is seen as a response to hosts that have evolved the ability to detect and reject odd-looking eggs in their nest. Surprisingly, some passerines that are not currently challenged by brood parasites still show this rejection behaviour when experimenters artificially introduce alien eggs into their nests. This rejection can reach levels of near 100% even when the added eggs are very similar to their own.

Influence of rearing hosts on host size acceptance by Trichogramma australicum

We investigated the acceptance of different sized host models by Trichogramma australicum in the laboratory. We used isoline cultures of T. australicum reared in hosts of different sizes. Helicoverpa armigera represent relatively large hosts, and those of Sitotroga cerealella are small, termed the Ha and Sc biotypes, respectively. Five sizes of glass beads were tested for acceptance: diameter 0.5, 0.75, 1.0, 1.5 and 2.0 mm. The acceptance of a host model was determined by persistent attempted drilling of a glass bead by a female. The relationship between host egg size and number of eggs laid by a female was also investigated. We used three sizes of artificial egg (diameter 0.75, 1.00, and 1.50 mm of hemispherical cupules) each containing artificial diet. Ha biotype wasps accepted host models in the range 0.75-1.50 mm dia. (vol. 0.166-1.325 mu l), whereas those of the Sc biotype accepted host models in the range 0.50-1.00 mm dia. (vol. 0.05-0.393 mu l). This evidence suggests a lineal (possibly genetic) influence to host size acceptance for T. australicum, dependent on the size of the host in which the wasp has been reared. Also T. australicum lay fewer eggs in smaller artificial eggs than in larger ones. The role of host size in host acceptance and number of eggs delivered, and its implications, is discussed.

Egg Removal by Brown-Headed Cowbirds: A Field Test of the Host Incubation Efficiency Hypothesis

Brown-headed Cowbirds (Molothrus ater) often remove host eggs, usually to the detriment of the host's reproductive success. We tested the hypothesis that host egg size and number influence the incubation efficiency of a parasitic egg. A single House Sparrow (Passer domesticus) or Brown-headed Cowbird egg was placed in each host nest (addition), and in some nests a host egg was removed as well (addition/removal). Hatching success and incubation length were measured to determine whether host-egg removal conferred an advantage in incubation efficiency compared to simple addition of a parasitic egg. Red­ winged Blackbirds (Agelaius phoeniceus) and Chipping Sparrows (Spizella passerina) served as medium-sized and small-sized host species, respectively. In Red-winged Blackbird nests, host-egg removal produced smaller clutches, and parasitic eggs had shorter incubation lengths in smaller clutches. However, the parasitic egg's incubation length and probability of hatching did not differ between the addition and addition/removal treatments. Parasitic eggs in Chipping Sparrow nests had shorter incubation periods than in blackbird nests and frequently caused the inefficient incubation of host eggs. Egg removal again did not reduce incubation lengths or increase hatchability of parasitic eggs. Thus, we found little support for the incubation efficiency hypothesis to explain host-egg removal by Brown-headed Cow­ birds.

Egg Parasitoids (Hymenoptera; Trichogrammatidae) of Diopsis Macrophthalma (Diptera; Diopsidae) in Malawi

In Malawi, during the study period eggs of the rice-borer Diopsis macrophthalma were mainly parasitized by Trichogramma kalkae and Trichogramma pinneyi and further by Trichogrammatoidea simmondsi and a Paracentrobia species. Data are presented on rates of parasitism, locations and sizes of parasitized eggs, fecundity, longevity, development time, number of exit holes, clutch size per host egg, sex-ratio, emergence rate,alternative hosts and super- and multiple parasitism. Relations are discussed between 1) development time and clutch size, 2) number of ♂♂ per host egg and exit holes, 3) oviposition rate and host egg size and 4) sex-ratio and clutch size. In the first three parasitoids mentioned a fertilization/oviposition system is found that favours the presence of one♂ and a certain number of ♀♀ per Diopsis egg. Evidence is put forward that a fixed sex-regulation system exists during oviposition. T. kalkae was the most important egg parasitoid of D. macrophthalma, followed by T. pinneyi. No other hosts were found for T. kalkae, whereas T. pinneyi had one alternative main host and some hosts of lesser importance. In competition for eggs of D. macrophthalma T. kalkae was in various ways superior to T. pinneyi. This latter species seems more adapted to smaller host eggs.

Effects of the copepod Cardiodectes medusaeus on the laternfish Stenobrachius leucopsarus with notes on hypercastration by the hydroid Hydrichthys sp.

Of the laternfish Stenobrachius leucopsarus collected, 2.7% were infected with the copepod Cardiodectes medusaeus. Coincidentally, 2.7% of the copepods were hyperparasitized by a hydroid, Hydrichthys sp. Copepod infection rates increase from Santa Barbara to San Diego, California. This increase may be due to a corresponding increase in the intermediate hosts. A comparison between the size classes of infected and uninfected fish suggests parasite-induced mortality. No relationship between the number of copepods per fish and host length was evident. Copepods were found in multiple infections up to five per host. A gregarious distribution of larval copepods and a nonspecific fibrotic response by the host is suggested. The copepod castrates its host. Multiple infection did not have an additive effect on host egg size nor did the presence of larval nematodes. A comparison of the total caloric content of copepods, infected and uninfected hosts, suggests that the copepod's energy demands on the host are negligible. The copepod appears to promote somatic growth of both female and male hosts.