The location of landmark leks in the small heath butterfly, Coenonympha pamphilus: evidence against the hot-spot model

Two major theories have been developed to explain the locationand evolution of leks. According to the hot-spot model leksare male initiated and occur because males aggregate at locationsof maximum female home range overlap. The alternative femalepreference model, on the other hand, assumes that leks are femaleinitiated, and that females prefer to mate with males that aggregate.Small heath butterfly leks are situated close to landmarks suchas trees and bushes in open grassland. Censuses of wild populationsand experiments with artificial landmarks showed that theirattractiveness increased with height and width measured at themiddle of tree height. Landmark width at field layer heightwas negatively correlated with attractiveness, which suggeststhat a cornet shape is preferred to a pyramid shape. Togetherthese landmark size variables explained 60% of variation inlek size. Release experiments showed that landmarks were approachedby receptive virgin females, but mated females were indifferentto them. Landmark use was correlated to microclimatic conditions.Males preferred wider landmarks during cooler weather. Theyalso competed for the lee side of landmarks. There was no correlationbetween the location of landmarks and the dispersion of matedfemales or emergence sites of females. Hence, receptive femaledispersion was largely determined by their mate-locating behavior,which in turn appeared to result from male dispersion. Leksmay initially have developed around easily detected visual cuesthat offered a more suitable microclimate for male activity.Females visiting these locations would find a suitable matemore rapidly and save valuable time for oviposition. Althoughnonadaptive evolution cannot be excluded, taken together theresults support the female preference model for lek evolution.     

The effect of host acceptability on oviposition and egg accumulation by the small white butterfly, Pieris rapae

The influence of host‐plant acceptability on oviposition rate, egg load, internal fat storage and longevity was studied in the small white butterfly, Pieris rapae L. (Lepidoptera: Pieridae). Newly emerged females and males were presented with either cabbage (Brassica oleracea L. var. gemmifera), which is a highly acceptable host for the small white, or wallflower (Cheiranthus cheiri L.), which is much less acceptable for oviposition. Individuals were dissected when 3, 6 and 9‐days‐old. Females kept on cabbage contained fewer mature eggs than those kept on wallflower and there was no change in the load of mature eggs over the time course studied. The number of immature eggs carried did not vary with host plant species, but did fall significantly between days 6 and 9. The body fat content of individuals declined with increasing age, but the decline was slower for individuals kept on the host of low acceptability. Individuals that were allowed to spend their natural lifespan on cabbage showed similar oviposition patterns over time, where the oviposition rate started high and gradually reduced until death. However, considerable differences in oviposition pattern were found in individuals kept on wallflower, varying from that found on cabbage to no oviposition at all. The implications of these findings are discussed in the light of existing oviposition theories. This leads to the conclusion that in one species the premises of existing theories on optimization of oviposition are not mutually exclusive but rather play in concert.     

Seasonal colour changes, sexual maturation and oviposition in Psylla peregrina (Homoptera: Psylloidea)

ABSTRACT.

• 1 Colour change is shown to be related to the timing of sexual maturation of P.peregrina Förster. Males become sexually mature and attain their autumnal coloration about 3 weeks before females.
• 2 Upon maturation males migrate down branches into the inner crowns of hawthorn trees. Females show a similar movement as they mature later in the season.
• 3 Seasonal colour changes may serve cryptic functions and are appropriate to the different environments in which adults are found during the season.
• 4 The distribution of overwintering eggs reflects the post maturation distribution of adult psyllids, with eggs being concentrated on old wood towards the base of hawthorn branches.

     

Effect of host deprivation on egg quality,egg load,and oviposition in a solitary parasitoid,Chetogena edwardsii (Diptera: Tachinidae)

Solitary parasitoids are limited to laying one egg per host because larvae compete within hosts. If host encounter rate is low, females should not increase the number of eggs/host in response. The tachinid fly, Chetogena edwardsii,was used to evaluate the effect of host deprivation on egg accumulation, oviposition behavior, and egg quality in a solitary parasitoid. Females deprived of hosts for 2– 7 days accumulate about 1 day's supply of eggs. Egg output of deprived females once hosts are restored does not differ from that of control females. Deprived females retain one egg in the uterus where it undergoes embryogenesis. Maggots emerging from retained eggs are more likely to survive in hosts molting in 40 h or less after receipt of an egg than are maggots emerging from eggs fertilized shortly before oviposition. Egg retention is a consequence of host deprivation that permits females to broaden the range of hosts they can exploit to include soon-to-molt hosts and possibly multiply parasitized hosts.     

Host-feeding and oviposition by parasitoids on hosts of different fitness value: Influences of egg load and encounter rate

A dynamic optimization model is presented for the decision to host feed or oviposit on hosts by female parasitoids. Optimal host utilization decisions are compared between two host types with different fitness payoffs for oviposition. The model predicts that hosts of higher fitness value should always be used for oviposition unless the egg load approaches zero. This general prediction is not influenced by levels of host availability or metabolic reserves, the age of the parasitoid, or the magnitude of the fitness difference. An egg-load threshold is predicted above which lower value hosts should be used for oviposition and below which they are used for host feeding. The position of this egg-load threshold is higher when the difference in fitness between host types is larger. The threshold is also higher when overall host availability is high or metabolic reserves for the production of new eggs are low. The threshold for oviposition on low-value hosts decreases to zero near the end of the parasitoid’s life. Under conditions where high-value hosts are rarely encountered compared to low-value hosts, the model predicts that lower value hosts should be accepted for oviposition at a lower egg-load threshold.     

Egg weight, batch size and fecundity of the spotted stalk borer, Chilo partellus in relation to weight of females and time of oviposition

The egg laying pattern of the spotted stalk borer on sorghum and maize, Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae) was studied during the first three nights of oviposition under laboratory conditions. More than 50% of both eggs and egg batches are laid during the first night of oviposition. Batch size decreases with time, whereas mean egg weight remains constant.Larger females lay both larger eggs and egg batches than smaller ones. They are also more fecund but it is only the second night of oviposition that contributes significantly to this difference.The reproductive effort decreases much with time. Allocation of reproductive reserves to early eggs seems more important than having eggs evenly distributed over time. Larger females use proportionally more resources to the production of late eggs. Large eggs are likely to contain more yolk which could be of importance for the ballooning behaviour of newly hatched larvae.

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Résumé La ponte de C. partellus Swinhoe a été étudiée au laboratoire pendant les trois premières nuits de la ponte. Plus de 50% des ooplaques et des oefs ont été pondus pendant la première nuit. La taille des ooplaques diminue avec le temps, tandis que le poids moyen des oeufs reste constant.Les grosses femelles pondent des ooplaques et des oeufs plus grands que les petites. Elles sont aussi plus fécondes, mais c'est seulement à la seconde nuit de ponte qu'est due cette différence.Le reproduction diminue beaucoup avec le temps. L'affectation aux premiers oeufs des réserves utilizées pour la reprodution semble plus importante que l'émission d'oeufs régulièrement répartis dans le temps. Les grosses femelles utilisent proportionnellement plus de ressources à la production d'oeufstardifs. Les gros oeufs contiennent vraisemblablement plus de vitellus que pourrait être nécessaire pour le comportement aérostatique des chenilles néonates.

     

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.     

The distribution of eggs per host in a herbivorous insect--intersection of oviposition, dispersal and population dynamics

1. The dynamics of parasitic organisms depend critically upon the frequency distribution of parasite individuals per host. However, the processes giving rise to this frequency distribution have rarely been modelled and tested for organisms with complex host selection behaviour. 2. In this study Microrhopala vittata, a chrysomelid beetle, was used to investigate how oviposition behaviour, movement and density of host plants interact in shaping the frequency distribution of egg clusters per host in the field. 3. Enclosures were stocked with two different host species and different beetle densities and various stochastic process models were fitted to egg cluster count data obtained from these enclosures. The different models were derived considering different scenarios, in particular whether or not plant density limits oviposition rate, whether or not ovipositing females actively seek out the most attractive plant within their perception radius and whether a female's oviposition rate is determined by plant intrinsic factors, the plant's egg cluster load or the surrounding beetle density. 4. The model parameters fitted to cage data were used to describe the frequency distribution of egg cluster counts obtained in a release experiment in the field. A total of 220 beetle pairs were released at five locations in a field where this beetle was not observed previously. Each release point was at a border between the two host species. 5. One model predicted for the preferred host species the egg cluster count frequencies in the field from parameters estimated in the cages. This model assumed that egg clusters present on a plant increased subsequent oviposition on this plant. All other models could not describe the distribution of egg cluster counts for either of the two host species. 6. The results suggest that females seek out attractive hosts actively and the attractiveness of a plant increases with its egg cluster load. This behaviour creates a frequency distribution of egg clusters per host that depends only on beetle density but not on plant density. This conclusion has important implications for modelling insect-plant interactions.     

Estimating cladoceran birth rate: use of the egg age distribution to estimate mortality of ovigerous females and eggs

The birth rate of natural cladoceran populations can change rapidly (during 2–3 days), reflecting rapid changes in their environment. If the egg ratio is calculated on the basis of egg age distribution, the birth rate can be estimated at short sampling intervals (shorter than egg stage duration) by modified Paloheimo's (1974) formula. When female size structure and age of eggs in clutches at the beginning and the end of a sampling interval are known, death rates of ovigerous females and eggs in separate size classes can be determined and incorporated in birth rate estimates. All these methods have been employed using the data on the population of Diaphanosoma brahyurum from the lake Obsterno (North-Western Belarus) in July–August, 1992. The birth rate values computed by the proposed methods and Poloheimo's formula differed significantly in many cases. The accuracy of birth rate estimations from various calculation methods was tested using a computer simulation. The model contains the essential features of cladoceran life history: distinct egg, juvenile and adult stages, development of eggs and reproduction. The population was divided into 25 age classes, each of 1 day duration. Durations of the egg, juvenile and adult stages were set at 3, 6 and 20 days, respectively. The embryogenesis was divided into three egg stages, each of 1 day duration. Survivorship was set from 0.2 up to 1.0 for each age class. The survivorship and brood size were changed through each of five time intervals (days) that allowed to simulate an increase or reduction of population density. Fecundity, survivorship and egg stage duration remained constant during each of 5 days that assumed stability of an environment (this does not occur in nature). Nevertheless, the egg ratio, proportion of juveniles and birth rates were variable even under these circumstances. Computer simulations showed that Poloheimo's formula evaluates birth rate with the relative error of 62% and usually overestimates its values. We propose methods to decrease errors of birth rate estimations by 3.5–5.5 times.     

Floral resources impact longevity and oviposition rate of a parasitoid in the field

1. The use of floral resource subsidies to improve herbivore suppression by parasitoids requires certain trophic interactions and physiological changes to occur. While the longevity and fecundity of parasitoids are positively affected by nectar subsidies in laboratory studies, the impacts of floral subsidies on the fecundity and longevity of freely foraging parasitoids have not been studied. 2. We studied the longevity and per capita fecundity of naturally occurring Diadegma insulare foraging in cabbage plots with and without borders of flowering buckwheat, Fagopyrum esculentum, as well as relationships between longevity, fecundity, sugar feeding and parasitism rates on larvae of the diamondback moth, Plutella xylostella. 3. Relative longevity was estimated by counting broken setae on the fringe of the forewing. Floral borders increased the longevity of males and females in adjacent cabbage plots. 4. The egg maturation rate of D. insulare was estimated by comparing egg loads of females collected early in the day with egg loads of females held without hosts in field cages throughout the day. Females in buckwheat cages matured 2.7 eggs per hour while females in control cages resorbed 0.27 eggs over the same time period. 5. The fecundity of females collected in the afternoon was estimated by comparing their actual egg load to the estimated egg load in the absence of oviposition for females in a given plot. Females foraging in buckwheat plots had marginally fewer eggs remaining in their ovaries, and laid marginally more eggs than females in control plots. Females from both treatments carried 30-60 eggs by the afternoon and therefore were time-limited rather than egg-limited. 6. Plots where a greater proportion of females had fed on sugar had longer-lived females. This suggests that feeding enhanced longevity of D. insulare. However, plots with longer-lived and more fecund females did not exhibit higher parasitism rates, although the power of these tests were low.     

Fertility and hatchability of eggs laid in the pullet-to-breeder transition period and in the initial production period

The initial eggs produced by broiler breeder hens are relatively small compared with later in the production cycle. An evaluation of indices related to hatchability is required when these eggs are to be used for the production of broiler chicks. Two experiments were conducted to evaluate characteristics related to the hatchability of eggs from pullet-to-breeder transition phase, at 25 and 27 weeks of age, and from the peak of production period and five weeks later, at 32 and 37 weeks of age. Eggs from birds 25 weeks had a lesser fertility in Experiment 1. Mortality occurred unevenly in early (1–5 days), middle (6–17 days) and late (18–21 days) incubation, and greater mortality was observed after the internal membrane was ruptured. The younger the hen, the lighter the egg, chick, and shell, and the longer the time required to complete the hatching process. In Experiment 2, greater mortalities were observed at the early period (1–5 days) and after “pipping” of the internal and external membranes. Embryos from heavy eggs of breeder hens 37 weeks of age took less time to complete the hatching process. Results indicated the larger the egg, the heavier the chick and shell, and the lesser the shell percentage. As breeder age advanced, characteristics related to egg fertility and hatchability improved.     

Host plant conspicuousness and the distribution of eggs and larvae in the butterfly,Anthocharis scolymus (Lepidoptera: Pieridae)

We investigated how the distribution pattern of eggs and larval on the host plant, Turritus glabra, was influenced by the oviposition behavior of the pierid butterfly Anthocharis scolymus. Females searched for the host plants visually and they frequently approached taller host plants with sparse surrounding vegetation. After encountering host plants, oviposition behavior of females was independent of host plant characteristics such as height, density, and type of surrounding vegetation. A female laid eggs singly on a host plants. Most females appeared to lay their eggs regardless of the presense of eggs on the host plant. Consequently egg and larva tended to be abundant on conspicuous host plants as measured by height or relative isolation from other plants. However, overcrowding of eggs on an individual host decreased the survival rate of larvae.     

Activity patterns and oviposition rates of Aphytis lingnanensis females,a parasitoid of California red scale Aonidiella aurantii: implications for successful biological control

1. Activity patterns of Aphytis lingnanensis Compere (Hymenoptera: Aphelinidae) females were determined. Females have a preovipositional period of 2–6.5 h and oviposit daily until they die. The average lifetime fecundity was 191 eggs (n = 10 females), with a maximum of 13 eggs per day, but usually far fewer. Females do not lay eggs at night as low light levels reduce the propensity to oviposit. 2. Aphytis lingnanensis females showed a repeatable pattern of activity during the course of the day, ovipositing actively during the first 1.5 h of their 7 h exposure to hosts. Thereafter, activity levels decreased sharply and females spent relatively long intervals resting. Activity occurred in fairly discrete bouts, with long periods of inactivity, ranging from 12 to 231 min between bouts. 3. Each day, females laid most eggs during their first bout of oviposition, with availability of mature eggs in the ovaries dictating the duration and intensity of ovipositional bouts. Once females completed a bout of oviposition in the laboratory, they moved away from the hosts even though many suitable hosts remained. They stood immobile, sheltering, until they matured more eggs. 4. These results suggest how general biological control models and dynamic state variable models of behaviour can be made more realistic. In particular, the behaviour of females does not remain constant over extended periods, particularly because of egg depletion, which suggests that the interaction between the ovipositional history of the individual and its physiological capabilities dictates the response of females to particular circumstances, and thus contributes to patterns of parasitism in the field. 5. It is predicted that A. lingnanensis females in the field are inactive at night and begin ovipositing when it becomes light enough in the morning. Egg depletion is likely if enough hosts are available, but should occur later in the day than was recorded in the laboratory. Egg-depleted females are likely to shelter while they mature more eggs, but may undertake interpatch movement.     

Age- and density-related oviposition behavior of the European corn borer,Ostrinia nubilalis (Lepidoptera: Pyralidae)

Age-related oviposition patterns ofOstrinia nubilalis were studied at three population densities in the laboratory by releasing newly eclosed adults in wire-screened cages and analyzing their oviposition throughout the adult stage with digital analysis. Oviposition sequences of individual females depositing egg masses were documented on the third and seventh nights after eclosion with a video camcorder. During a sequence, a female produced an egg in an average time of 15 or 26 s on the third and seventh nights, respectively, and completed depositing an egg mass the size of 20–39 eggs in an average time of 316 and 525 s, respectively. Females were not easily disturbed during egg mass deposition and pulsated their abdomen before deposition of each egg. Females produced few egg masses the first night after eclosion. Oviposition increased on nights 2 and 3 but declined steadily thereafter as females matured. Females older than 6 nights produced fewer egg masses; the proportion of egg masses with fewer than 20 eggs increased gradually. By the end of the adults' lifetime, nearly 100% of the egg masses had fewer than 20 eggs. The data are fundamental to our research to define the role of phytochemicals in modifying oviposition behavior of the European corn borer.     

Foliar form, colour and surface characteristics influence oviposition behaviour of the carrot fly

Various leaf models made of paper were presented to carrot flies, Psila rosae (F.) (Diptera: Psilidae) in choice assays to investigate the effect of non-chemical plant traits on oviposition behaviour. The surrogate leaves differed in colour, shape, surface coating, size and stem length. In the presence of host-plant extracts, physical factors strongly influenced oviposition. Green, yellow and orange three-dimensional models similar in shape to host-plant leaves (pinnately or ternately compound or dissected) and with a thin cover of paraffin wax were most acceptable to the females. Egg-laying was not affected by leaf size, but was negatively correlated with stem length. The results obtained by testing models with simple leaf silhouettes were confirmed in an experiment using more lifelike imitations of real host and non-host leaves. The findings are discussed by an extensive review of similar studies in three other phytophagous fly species (cabbage root fly, onion fly, Hessian fly).     

Foliar form, colour and surface characteristics influence oviposition behaviour in the cabbage root fly Delia radicum

The effects of foliar form, colour and surface characteristics on the oviposition behaviour of the cabbage fly were investigated by presenting females with various leaf models made of paper. The models differed in shape, size, colour, surface coating, the presence of 3 dimensional folds and a stem. It was shown that in the presence of host leaf surface extracts physical factors can strongly influence oviposition behaviour. Females laid the most eggs around the base of bright green or yellow models having a stem, vertical folds and covered with a thin layer of paraffin. The vertical folds in the surface increased the chance of a behavioural transition from leaf run to stem run.

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Zusammenfassung Mit Hilfe von Papiermodellen von Kohlblättern wurde der Einfluss von visuellen und mechanischen Eigenschaften des Blattes auf das Eiablageverhalten der kleinen Kohlfliege, Delia radicum, untersucht. Die verwendeten Modelle unterschieden sich in Form, Grösse, Farbe, Oberflächen struktur und Stiel des Blattes. Es wurde gezeigt, dass physikalische Reize zusammen mit den chemischen Stoffe auf der Blattoberfläche stimulierend wirken. Ein natürliches Eiablageverhalten und die stärkste Eiablage wurde durch ein Modell ausgelöst, welches sich durch leuchtend grüne Farbe, Stiel und vertikale Falten und einen Paraffinnüberzug auszeichnete.

     

Factors affecting oviposition rate in the flour beetleTribolium castaneum and the origin of the population regulation mechanism

The effects of egg cannibalism, conditioned medium and the presence of quinone secretions on oviposition rate were studied using single pairs of adults to eliminate any direct crowding effects. Most measurements were made on beetles confined to the surface of the flour medium in plastic towers. Oviposition rate was decreased by about 58% when pairs were transferred from fresh to conditioned medium; lowered about 25% when only quinones were present and the medium was still fresh; and enhanced 35% in dry conditions when beetles were provided with eggs to eat. Both the lowered oviposition rate in confined cultures and egg-eating may be explained by natural selection at the individual level. Cannibalizing eggs boosts a female's oviposition rate. The presence of quinones or conditioned medium indicates high population densities and acts as a signal for ceasing oviposition and dispersing to avoid high egg mortality. In confined populations, this results in population regulation, while in open populations, this strategy is a mechanism to avoid competition. It implies that the resource shortages normally experienced by such organisms are relative, not absolute.     

Tyramine from the leaves of wild parsnip: a stimulant and synergist for oviposition by the black swallowtail butterfly

Abstract .Oviposition stimulants from the foliage of wild parsnip, Pastinaca sativa (Apiaceae), were isolated by column chromatography and HPLC and tested in bioassay experiments with hand-held female black swallowtail butterflies, Papilio polyxenes (Lepidoptera: Papilionidae). Two of the stimulants were identified as tyramine and trans -chlorogenic acid. A combination of tyramine, trans -chlorogenic acid and an active neutral fraction was needed to elicit a significant oviposition response. These results are discussed in the context of previous research on the oviposition stimulants of swallowtail butterflies and on the significance of tyramine as a neuromodulator of physiological processes in invertebrates.     

Constituents of host- and non-host plants deterring oviposition by the cabbage butterfly, Pieris rapae

Oviposition by Pieris rapae L. on cabbage was deterred by homogenized cabbage tissue sprayed onto intact plants. Ether extracts of cabbage also were deterrent, but water extracts were not. Hexane extracts of other host plants deterred oviposition and water extracts had little or no effect. Polar as well as non-polar extracts of non-host plants inhibited oviposition. Polar deterrents in the non-host crucifers, Erysimum cheiranthoides and Capsella bursa-pastoris may explain the avoidance of these plants by P. rapae. Chemical deterrents, as well as stimulants, apparently play a major role in the acceptance or rejection of plants as hosts by ovipositing female butterflies.

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Zusammenfassung Die Eiablage von Pieris rapae auf Kohl wurde gehemmt von einem Homogenisat aus Kohlblättern, das auf intakte Pflanzen gesprüht wurde. Ether-Extrakte der Kohlblätter wirkten im Gegensatz zu Wasserextrakten abschreckend. Ebenso zeigten Hexanextrakte anderer Wirtspflanzen eine hemmende Wirkung auf die Eiablage, während Wasserextrakte anderer Wirtspflanzen keine Wirkung aufwiesen. Dagegen aber verhinderten sowohl polare als auch unpolare Extrakte von Nicht-Wirtspflanzen die Eiablagen. Polare, abschreckende Substanzen in den Nicht-Wirtspflanzen Erysimum cheiranthoides und Capsella bursa-pastoris (Cruciferae) könnten Ursache dafür sein, dass P. rapae diese Pflanzen meidet. Chemische Substanzen mit sowohl abschreckender als auch stimulierender Wirkung spielen offensichtlich eine bedeutende Rolle für legebereite Schmetterlingsweibchen bei der Auswahl von Pflanzen als geeigneten Eiablageplatz.