Models of clutch size in insect oviposition

Models for clutch size in species where a female deposits eggs into a larval resource of limited carrying capacity are developed. Previous models of clutch size related mainly to vertebrates (notably birds) where parental care limits clutch size. Our models cover cases where a single female “saturates” a larval food patch with larvae. The main predictions are that (1) extra eggs should be laid to compensate for larval moratility; (2) clutches should generally be smaller than the size that yields the maximum number of surviving larvae/clutch; (3) in species that gain resources for eggs in the adult stage, clutch size will be unaffected by age-independent parental mortality between clutches; (4) clutch size should reduce throughout life in species that gain resources for eggs before the adult stage; (5) similar species, but which are constrained to produce constant-sized clutches, should lay smaller clutches if their total potential egg production is low; (6) clutch size should increase with increasing search costs for oviposition sites. An ESS model of double-oviposition (where two females sometimes lay in the same larval food patch) indicates that the first female should generally lay more eggs than the second female; the difference in clutch size should decrease as the probability of double-oviposition increases, and should decrease as the search costs for larval food plants decreases. Many of the predictions have some support from data on insect oviposition.     

Adaptive decision making or differential mortality: what causes offspring emergence in a gregarious parasitoid?

Hosts represent a limited resource for the developing offspring of parasitic insects laying eggs in or on spatially discrete resources like fruits, seeds, or other insects. The quality of hosts differs with respect to the value and amount of resources they provide for the feeding larvae. Accordingly, the size of a clutch of eggs laid on a given host should be a function of host quality, because severe competition between developing larvae can lead to increased mortality and/or decreased size of the offspring, both causing a fitness loss for the offspring and the mother. Therefore, females should be selected for the ability to estimate host quality and to adjust their clutch size accordingly. Using the parasitic wasp Nasonia vitripennis (Walker) (Hymenoptera: Pteromalidae) this study investigated the respective contribution of developmental mortality of offspring vs. the clutch size decision of the mother as a determinant of final offspring emergence per host. In addition, taking offspring size into account, the study examined the fitness consequences of female oviposition decisions. Developmental mortality was very low in all quality classes of hosts except previously frozen and thus dead host pupae. Females laid reduced clutch sizes on dead, previously parasitized, and smaller hosts. In contrast to offspring number, offspring size did not differ between host qualities. We conclude that females are able to sense the quality of a host and adjust the number of eggs they lay to mitigate larval competition.     

Resource-Dependent Clutch Size Decisions and Size-Fitness Relationships in a Gregarious Ectoparasitoid Wasp, <Emphasis Type="Italic">Bracon brevicornis</Emphasis>

Gregarious parasitic wasps, which lay more than one egg into or onto a host arthropod’s body, are usually assumed to lay an optimal number of eggs per host. If females would lay too few eggs, some resources may be wasted, but if females lay too many eggs, offspring may develop into substantially smaller-sized adults or may not develop successfully and die. The availability of hosts can further influence a female’s clutch size decision, as more eggs should be laid when hosts are scarce. Here, we analyzed clutch size decisions and the fitness consequences thereof in the ectoparasitic wasp Bracon brevicornis (Hymenoptera: Braconidae), a potential biocontrol agent against pest moth species. For experiments, larvae of the Mediterranean flower moth, Ephestia kuehniella (Lepidoptera: Pyralidae) were used. Using artificially created as well as naturally laid clutches of eggs, the effects of clutch size on fitness of first (F1) and second (F2) generation offspring were investigated. Our results revealed that the fitness consequences of large clutches included both increased mortality and smaller adult sizes of the emerging offspring (F1). Smaller F1 females matured fewer eggs during their lifetime and their offspring (F2) had reduced egg-to-adult survival probability. Naturally laid clutches varied with host size up to a maximum, which probably reflects egg limitation. Clutches remained smaller than the calculated optimal (Lack) clutch size and females responded to high host availability with a decreased number of eggs laid. We thus conclude that large clutches may result in significantly smaller offspring with reduced fitness, and that host size as well as host availability influence the clutch size decision made by B. brevicornis females.     

The influence of competition between foragers on clutch size decisions in an insect parasitoid with scramble larval competition

The effect of competition between ovipositing females on theirclutch size decisions is studied in animals that lay their eggsin discrete units of larval food (hosts). In such species theeffect of competition depends on the form of the larval competitionwithin such units. In insect parasitoids, there might eitherbe contest (solitary parasitoids) or scramble competition (gregariousparasitoids) between larvae within a host For gregarious parasitoids,a decreasing clutch size with increasing competition betweenforagers is predicted. This prediction is tested in experimentsusing the parasitoid Aphaertta minuta. Parasitoids were eitherkept alone or in groups of four before the experiment, in whichthey were introduced singly in a patch containing unparasitizedhosts. Animals kept together laid on average clutches of 0.74eggs smaller than females kept alone (average clutch is 5.3),thereby confirming the prediction. Clutch size decreased withencounter number, which might be due to the adjustment of thefemale's estimate of the encounter rate with hosts. Finally,the results are compared with those reported for solitary parasitoids(that have scramble larval competition), for which it is predictedthat the clutch size will increase with increasing levels ofcompetition between females.     

Influence of Conspecific Presence, Experience, and Host Quality on Oviposition Behavior and Clutch Size Determination in Anastrepha ludens (Diptera: Tephritidae)

Females of some insect species adjust the number of ovipositions and clutch size adaptively depending on conspecific density and probably experience. In a series of three experiments, we examined the effect of the presence of conspecifics, host quality, and oviposition experience on oviposition behavior and clutch size determination by females of the polyphagous fruit fly Anastrepha ludens (Diptera: Tephritidae). In the first experiment, we determined that grouped (eight females per cage) A. ludens females tended to visit and oviposit in more hosts than did solitary females probably as a result of stimulation by the presence of conspecifics. We also determined that females with previous oviposition experience visited and oviposited in more hosts than inexperienced ones. Importantly, when females were grouped, we observed significantly more landings on unoccupied hosts (i.e., devoid of flies) than on occupied ones (i.e., with at least one fly on it). However, oviposition experience, and not female density, was the most important factor affecting clutch size. Naive females deposited larger egg clutches than experienced ones. In the second experiment, we found that oviposition experience and host quality (i.e., clean fruit or fruit covered with a host marking pheromone [HMP] extract), influenced clutch size and the decision of females to defend or not defend the host. Clutch size and number of fights were greater on clean than on HMP-marked hosts. In the third experiment, we observed that host quality (i.e., size) played a significant role with regard to the number of female fights, host marking behavior, and clutch size. Specifically, females fought and dragged their aculeus longer on small- and medium-sized hosts than on large ones. But this behavior varied according to whether females were kept alone or grouped. Clutch size was greatest in the largest hosts. Considering all the above, we believe that the observed increase in ovipositional activity by grouped A. ludens females can be attributed to competition through mutual interference and not social facilitation as has been reported in other tephritid species.     

Superparasitism strategies by a native and an exotic parasitoid species attacking the Mexican fruit fly,Anastrepha ludens (Diptera: Tephritidae)

Superparasitism refers to the action of parasitoids ovipositing eggs in hosts that are already parasitized; this inevitably results in the elimination of supernumerary larvae in solitary parasitoids. Here, we investigated superparasitism performed by two species of solitary parasitoids on the larvae of Anastrepha ludens (Loew; Diptera: Tephritidae): a native species, Doryctobracon crawfordi (Viereck; Hymenoptera: Braconidae), and an exotic species, Diachasmimorpha tryoni (Cameron; Hymenoptera: Braconidae). Tests were conducted under laboratory conditions evaluating the behaviour of females acting alone (self-superparasitism) or in groups (conspecific superparasitism). Parasitism strategies were different between these two species. In D. crawfordi, the number of first instar larvae found in each dissected host pupa was never greater than two, regardless of the number of oviposition scars observed per pupa. In contrast, there was a positive correlation between the number of oviposition scars and the number of first instar larvae in D. tryoni. The survival and fecundity of D. crawfordi females emerging from pupae with one scar was higher than in females emerging from pupae with more scars. In D. tryoni, the number of oviposition scars did not show deleterious effects on life history traits and was positively correlated with the proportion of emerging females. An understanding of the superparasitism strategy adopted by parasitoid species could be of great interest to augmentative biological control programmes because the mass rearing of natural enemies could be negatively or positively affected by this condition.     

Egg and larval load assessment and its influence on oviposition behaviour of the leaf beetle Galerucella nymphaeae

The oviposition behaviour of the water-lily beetle Galerucella nymphaeae was examined. This species is a specialist herbivore on the floating leaves of nymphaeids Nymphaeaceae and especially on the yellow water-lily, Nuphar lutea. Females lay their eggs in clutches on the leaves, and after hatching, the larvae feed on the leaves. The quality of the leaves decreases quickly after the larvae hatch, and eventually the leaves will sink below the water surface, whereupon the eggs, 1st-instar larvae and pupae are killed by drowning. The influence of conspecific eggs, larvae and feeding tracks on the oviposition preferences of the beetles was tested. Females were allowed to choose between fresh leaves and leaves with conspecific eggs and larvae as well as between leaves with larvae and leaves with feeding tracks but no larvae. An attempt was also made to determine whether eggs and larvae affect the oviposition rate of females when they are not given the opportunity to oviposit on untouched leaves. The results indicate that females tended to avoid leaves with conspecific larvae or to exhibit a decreased oviposition rate on such leaves. Females also avoided conspecific eggs, although the oviposition rate was not influenced by the presence of conspecific eggs. When females were allowed to choose between leaves with larvae and leaves with feeding tracks, possible discrimination against leaves with larvae just fails to reach the 5% level.     

Field superparasitism by Diachasmimorpha longicaudata attacking Anastrepha spp. larvae on mango fruits

The incidence of superparasitism in field populations of Diachasmimorpha longicaudata (Ashmead), a solitary larval–pupal endoparasitoid, attacking Anastrepha fruit fly species was determined. From 14,550 fruit fly larvae infesting mango fruits in the field, 68.9% (10,038) survived to the pupal stage. Of these pupae, 3780 (37.7%) were parasitized, of which 2075 (54.9%) were superparasitized. The number of oviposition scars per pupa ranged between 1 and 29, although high numbers were rare. The presence of one or two scars per host was frequent, but only 8.6% of pupae had more than three scars. Fruit size was positively related to the level of infestation by Anastrepha spp. and was significantly correlated with the numbers of parasitized and superparasitized pupae by D. longicaudata. The length and width of host pupae were positively related to superparasitism, and superparasitism was positively correlated with a sex ratio biased toward females. Our data show that superparasitism is present in natural populations of D. longicaudata at remarkable rates and confers some advantageous features such as a female-biased sex ratio. These findings favor the election of this species as a viable biocontrol agent for augmentative releases because the favorable proportion of adult females emerging from superparasitized pupa should contribute to better pest control.     

Manipulation of laying effort reveals habitat-specific variation in egg production constraints in Great Tits (Parus major)

It has been suggested that a bird's clutch size is not limited by the amount of resources available at the time of laying but that differences in the availability of food for nestlings is the ultimate underlying factor determining spatio-temporal variations in clutch size. However, habitat-related variations in egg production ability has yet to be investigated explicitly. We studied the breeding of Great Tits Parus major in deciduous and coniferous forests in the same area. The sizes of both the clutches and the eggs were, on average, larger in the former habitat than in the latter. A number of females were induced to lay more eggs than usual by removing four eggs from designated experimental clutches early in the laying period. These manipulated females laid approximately one egg more than control females, with the number of additional eggs laid not differing between the habitats. However, in both study years the relative size of the extra eggs – relative to the mean size of earlier laid eggs of the same clutch – was smaller in the coniferous habitat than in the deciduous habitat, while there was no habitat-related difference in the relative size of the last-laid eggs of control clutches. This result indicates that some form of proximate limitation during egg-laying period can contribute to the relatively small clutches and eggs in the coniferous habitat. Our results emphasize the need to take egg production costs into account when attempting to account for spatial variation in the reproductive behaviour of birds.     

The avoidance of superparasitism in four species of parasitic wasp—Mathematical models and experimental results

Experimental results, and interpretation, are presented which relate to oviposition behaviour in four species of parasitic wasp (Hymenoptera: Chalcidoidea). All lay their eggs in pupae of the common house fly (Musca domestica) and of other flies associated with man. Probability models suggested byD. J. Daley for describing the avoidance of superparasitism are used to analyse the data. Certain of the models considered by previous authors appear as specieal cases. A satisfactory fit was obtained either by assuming a fixed probability of oviposition in an already parasitised pupa, or by using a model motivated by supposing that a female will tolerate without oviposition some fixed number of visits to already parasitised pupae. A third model was considered which makes the probability depend on the number of previous ovipositions in the pupae now visited. In all four species the presence of other females (with parasite: host ratio unchanged) increased the probability of oviposition upon encountering an already parasitised pupa. In the presence of other females Spalangia endius laid an increased number of eggs, whereas the other three species laid fewer eggs.     

Larval Competition, Adult Fitness, and Reproductive Strategies in the Acoustically Orienting Ormiine Homotrixa alleni (Diptera: Tachinidae)

Homotrixa alleni is a gregarious endoparasitoid fly that attacks adult male Sciarasaga quadrata (Orthoptera: Tettigoniidae) in southwestern Western Australia. Gravid female flies acoustically orient to their host's call and deposit live first-instar larvae upon or near their calling host. Up to 16 larvae may be found developing in the one host, and since only calling adult male S. quadrata are parasitized, host size and hence larval resources are essentially fixed at parasitism. This study examines parasitism by H. alleni in relation to intraspecific larval competition and adult fitness. The mean number of larvae emerging per host failed to increase significantly beyond a clutch size of four. Mean pupal weight and survival to the adult stage decreased linearly with increasing clutch size across the entire range of clutch sizes examined. Within a clutch, heavier pupae successfully completed pupal development significantly more often than lighter pupae. Pupal weight was directly related to adult size, with adult males being significantly larger than adult females at any given pupal weight. Female body size was positively correlated with fecundity. The size distribution of emerging females was normally distributed, while the distribution of searching gravid females collected at acoustic traps in the field was significantly skewed toward larger flies, suggesting yet another fitness benefit associated with large size. Using fecundity and survival to adulthood as our measure of fitness we calculated the optimal clutch size maximizing fitness per host to be seven, which exceeds the majority of observed clutch sizes in the field. Uncertainties associated with larvae successfully entering the host following larviposition are likely to reduce clutch sizes of H. alleni below this optimum in the field.     

Host size,superparasitism and sex ratio in mass-reared <Emphasis Type="Italic">Diachasmimorpha longicaudata</Emphasis>, a fruit fly parasitoid

We analyzed the relationship among host size, superparasitism and sex-ratio in mass reared Diachasmimorpha longicaudata (Hymenoptera: Braconidae). Individual host pupae of Anastrepha ludens (Diptera: Tephritidae) were measured (length and width), and the number of oviposition scars per pupa was used as a reliable indicator of superparasitism. The probability of an emerging parasitoid being a female was positively associated with the number of oviposition scars on the host cuticle, but not with the host size. The number of scars per host pupae from which females emerged was slightly but significantly higher than in those pupae giving raise to males. In D. longicaudata, the influence of host size on sex allocation decisions of individual females seems to be overridden by the level of superparasitism, which itself was positively correlated with pupa length. This suggests that larger pupae could experience a higher number of ovipositions than their smaller counterparts, and that a high level of superparasitism may conduct to a female biased sex ratio. We discuss the relevance of these findings which could provide new elements (e.g., the manipulation of superparasitism) for optimizing the mass rearing of this parasitoid.     

FACTORS AFFECTING THE EGG SIZE OF RED-BILLED GULLS LARUS NOVAEHOLLANDIAE SCOPULINUS

The factors influencing the egg size of the Red-billed Gull Larus novaehollandiae scopulinus were studied at Kaikoura, New Zealand, between 1964 and 1972. In two- and three-egg clutches there was a trend for the eggs to become smaller in the sequence of laying. Length, breadth and volume of eggs of one-, two- and three-egg clutches declined significantly as the season progressed. The size of eggs from single-egg clutches tended to be smaller than eggs from two-egg clutches laid at the same time. There were correlations between the proportions of one-egg and of three-egg clutches being laid at a given period and the mean egg volume of two-egg clutches. When the mean egg volume of two-egg clutches increased there was a corresponding increase in the proportion of two- and three-egg clutches laid. When the mean egg volume of two-egg clutches decreased there was an increase in the proportion of single-egg clutches laid. The egg size of the Red-billed Gull showed no direct correlation with the abundance or availability of food; the largest eggs were produced early in the season when food was in short supply. In spite of an increase in the food supply in the middle of the breeding season, birds laying at this time produced smaller eggs than birds which laid earlier in the season. However, early breeders which relayed at the peak in food abundance on average produced a larger replacement clutch than originals laid early in the season. It is suggested that the birds nesting early in the season are able to produce the largest eggs because they are the most efficient foragers for food, and those which nest later in the season produce smaller eggs, even at peak food abundance, because of their inefficiency or inexperience. Early breeders laying replacement clutches tended to lay larger eggs and larger clutches than birds which are producing their first clutches at the same time. Two-year-old females laid eggs which were significantly shorter than older aged birds while the breadth and volume of the egg increased with the age of the female up to the fifth year. There was a trend for females to lay larger eggs when mated with older rather than younger males. No statistical differences in egg size were detected between females changing or retaining the partner of the previous season. Female body weight and egg volume were positively correlated in females weighing less than 275 g but not for heavier females. It is suggested that the seasonal decline in egg size and clutch size results from a decrease in the availability of food and the ability of the individual to exploit the resource.     

Parasitism-induced Effects on Host Growth and Metabolic Efficiency in Tobacco Hornworm Larvae Parasitized by Cotesia congregata

Parasitism by the braconid wasp Cotesia congregata affects the growth of Manduca sexta larvae in a parasitoid 'dose-dependent' fashion. Following parasitization of fourth-instar larvae, more heavily parasitized larvae grew larger compared to those containing fewer parasitoids due to an increase in host dry weight. The differences in host mass appeared to arise after oviposition. A 'dose-dependent' enhancement of host dry weight would appear nutritionally beneficial for the parasitoids developing in more 'crowded' hosts. The efficiencies of conversion of ingested and digested food to body mass and the approximate digestibility of the diet ingested by the host caterpillar did not vary significantly with clutch size although parasitoids took slightly longer to develop in the more heavily parasitized hosts. Larval parasitoids developing in the presence of many competitors weighed up to 50% less than those developing in hosts with fewer endoparasitoids, although the weight of adult female parasitoids did not vary significantly with wasp clutch size. The maximum number of emerging wasps was 200 parasitoids, possibly representing the host's 'carrying capacity' for larvae parasitized in the fourth-instar. The ratio of emerging to non-emerging parasitoids decreased as parasitoid clutch size increased, with few or none emerging from very heavily parasitized hosts containing more than 400 parasitoids. Copyright 1997 Elsevier Science Ltd. All right reserved     

The problem of optimal clutch size in a tritrophic system: the oviposition strategy of the thistle gallfly Urophora cardui (Diptera,Tephritidae)

The problem of optimal clutch sizes is a central theme in life history theory. Optimal allocation of eggs is especially complicated for insects in tritrophic systems. In this study we analyze some of the processes determining clutch sizes of the thistle gallfly Urophora cardui, a monophagous tephritid fly associated with Cirsium arvense. U. cardui forms multilocular shoot galls, which vary broadly in their size and number of their gall cells. We investigate various fitness consequences of gall size. An analysis of the number of cells per gall (which is correlated with gall diameter and gall weight) showed that in U. cardui there is mutual facilitation rather than larval competition. Increasing numbers of larvae per gall led to a decreasing mortality and increasing larval weight. Larval weight in turn was positively correlated with the probability of survival to adulthood and with adult weight and fecundity. Thus, all fitness parameters measured favoured large galls. Clutch sizes in oviposition experiments were distinctly larger than the number of gall cells of field populations and in cage experiments, suggesting high mortality of eggs and/or early larval instars. There was a significant relationship between the internal structure (i.e., the size of the growing point) of the bud and clutch size, suggesting that U. cardui females are able to measure bud quality and adapt clutch sizes accordingly. Clutch size was positively correlated with the female's age at first oviposition and negatively with the number of previous ovipositions and previously laid eggs. Since the potential egg capacity per female is higher than the average number of larvae it is likely to produce during its short adult lifespan, U. cardui females tend to be time-limited rather than egglimited, which might favour large clutches once an appropriate oviposition site has been located. As the development of the gall and hence the fate of a clutch depends on a number of unpredictable factors, exclusive concentration of eggs in a few large clusters would involve risks which could be avoided by increasing the number of clutches. Therefore we interpret the high variation of clutch sizes in U. cardui as a mixed strategy of bet hedging and gambling.     

Fecundity and oviposition ofEucelatoria bryani, a gregarious parasitoid ofHelicoverpa zea andHeliothis virescens

We examined longevity, fecundity, and oviposition strategies ofEucelatoria bryani Sabrosky (Diptera: Tachinidae), a gregarious endoparasitoid ofHelicoverpa zea (Boddie) andHeliothis virescens (F.) (Lepidoptera: Noctuidae). Longevity of adult femaleE. bryani was not related to body size. In contrast to longevity, largerE. bryani females had greater potential fecundity than smaller females, as determined by the number of embryonated eggs present in the common oviduct. However, female parasitoid size did not affect primary clutch size (number of eggs deposited in a host). Because embryos in eggs located in the ovisac were larger than those located elsewhere in the common oviduct, maximum primary clutch size may be physiologically limited by the number of fully mature eggs a female has available at one time.E. bryani females adjusted primary clutch size in response to host size, for bothH. zea andH. virescens. This adjustment appears to be adaptive because females did not overexploit hosts by depositing more larvae than a host could support. Adult emergence was not related to host size. Although host weight positively influencedE. bryani progeny weight, increases in progeny size with host size were counterbalanced by increases in primary clutch size with host size.     

Gregarious Oviposition and Clutch Size Adjustment by a Heliconius Butterfly1

Female Heliconius hewitsoni butterflies were found to aggregate during oviposition, producing multi‐parent egg clutches. This behavior occurred when host plants were locally plentiful, indicating that females chose to oviposit gregariously. Collective clutch size correlated with host growth rate and with the number of females contributing to a clutch. Eggs did not positively bias host plant growth. Collective clutch size adjustment may represent a mechanism for facilitating larval aggregation while reducing intraspecific competition.     

Influence of egg size differences within egg clutches on larval parameters in nine libellulid species (Odonata)

Abstract.  1. In libellulids, egg size differs between species and populations. There are also size differences within egg clutches of individual females.
2. Past experiments suggest that there are two different types of egg clutches in libellulids. Egg size decreases significantly during oviposition in species that perform non-contact guarding during oviposition. In contrast, in species ovipositing in tandem, egg size is randomly distributed.
3. This study deals with the possible consequences of egg size variation within the different egg clutch types. The study examined whether there is a correlation between egg development time, offspring sex or larval size and egg size.
4. The current experiments were conducted in Namibia and Germany. Five non-contact guarding and four tandem guarding libellulid species were used.
5. In some species larger eggs needed more time to develop, in some species no correlation between egg size and egg development time could be found, whereas in other species larger eggs developed faster.
6. The sex ratio was biased towards females in Leucorrhinia dubia and in Sympetrum striolatum and egg size was not associated with gender.
7. In both egg clutch types larger eggs resulted in larger larvae. In this study, evidence was found that the effects of egg size diminished with progressing larval development under good conditions. However, it is possible that the effects may have a greater influence under harsh circumstances.     

Postemergence Experience Affects Sex Ratio Allocation in a Gregarious Insect Parasitoid

We tested the hypotheses that postemergence experience with plants (“early adult learning”) modifies sex ratio and clutch size allocations of Cotesia congregata (Say) (Hymenoptera: Braconidae), a gregarious larval endoparasitoid of Manduca sexta L. (Lepidoptera: Sphingidae). Emerging wasps were exposed for 2–3 h to (a) one of two host plants (tomato or tobacco) or no plant, and (b) one of two novel plants (arugula or parsley) or no plant. Each female was permitted a single oviposition in a host offered with one of the two plant species 24 h later. Hosts were reared on laboratory diet before and after parasitization. Wasps exposed to either host plant allocated proportionately more females to hosts offered with the plant species experienced at emergence than wasps with the alternate species, but clutch sizes did not differ. Irrespective of plant species, wasps exposed to novel plants allocated proportionately more females to hosts than wasps without plant experience, and larger clutches to hosts offered with parsley than with arugula. Differential responses to host and novel plants suggest inherent recognition of host foodplants by C. congregata. Results demonstrate a direct effect of learning on reproductive potential.     

Maternal behavior and clutch manipulation in the ring-legged earwig (Dermaptera: Carcinophoridae)

The expression and maintenance of maternal behavior in the earwig,Euborellia annulipes, was examined through manipulation of clutch size, age, and species and through observations of interactions between brooding females. Females underwent discrete gonadotrophic cycles culminating in oviposition of first clutches that were highly variable in size. Neither the head capsule width nor the age of the mother was correlated with clutch size. Maternal care extended through embryogenesis and for the week following hatching. Clutch removal significantly shortened the interclutch interval, indicating that the presence of brood inhibited the onset of the second gonadotrophic cycle. Brooding females readily accepted replacement clutches of the same age. Thus, mothers did not appear to distinguish their own eggs from those of other females. Experimental doubling of clutch size did not significantly reduce the proportion hatching or fledging. In contrast, reducing clutch size diminished the percentage successfully fledging. Manipulation of clutch age resulted in reduced hatching/fledging success. Placing two females, each with newly laid clutches, in the same cage usually resulted in egg transfer from the nest of one female to that of the other within 12 h. Nests of females with larger forceps were significantly more likely to contain both clutches. When mothers with first clutches were paired with mothers with third clutches, eggs were more likely to be transferred to the nest of the older female.E. annulipes females with newly laid clutches appeared to accept as replacement clutches eggs of the earwigDoru taeniatum. Alien clutches were maintained for the typical duration of embryogenesis; however, noD. taeniatum hatchlings were observed.