The function of multiple mating in oviposition and egg maturation in the seed beetle Callosobruchus maculatus

Abstract.  To comprehend the significance of multiple mating in female Callosobruchus maculatus , the material-benefits hypothesis is tested, as well as the potential function and mechanism of additional mating for females. The results show that longevity and lifetime fecundity are significantly higher in doubly-mated females, whereas females subject to an interrupted second copulation (which transfers no ejaculate) show resemblance with singly-mated females in lifetime fecundity and daily fecundity, supporting the material-benefits hypothesis. Female lifetime fecundity increases with ejaculate size in doubly-, but not singly-mated females. Doubly-mated females exhibit an immediate increase in fecundity on the day of remating. Moreover, dissection of ovaries after remating shows that the number of unlaid eggs is lower in doubly-mated females in comparison with singly-mated females, whereas the total number of unlaid and laid eggs shows no significant difference. This suggests that the second mating increases the oviposition rate, but not the egg maturation rate in female C. maculatus . Thus, ejaculate serves as a stimulus for oviposition, at least on the remating day. However, because doubly-mated females lay more eggs in total than singly-mated females, doubly-mated females appear to mature more eggs than the singly-mated counterparts. This is attributed to the 'indirect-driven' hypothesis, which states that the reduction in the number of mature eggs in the oviducts brought about by oviposition stimulates the maturation of oocytes in ovarioles to replenish the number of mature eggs.     

Ability of ovipositing seed beetles to discriminate between seeds with differing egg loads

Abstract. 1. Previous work has shown that ovipositing females of Callosobruchus maculatus (F.) avoid seeds already bearing eggs, and thereby reduce competition among their larval progeny within seeds.
2. This study demonstrates that females also detect small differences in egg density, and prefer to oviposit on seeds with a lower-than-average number of eggs. A nearly uniform dispersion of eggs is thus maintained even after all seeds bear several eggs.
3. In addition, variation in egg load influences oviposition rate. Transfer of females from seeds with few eggs to seeds with many eggs inhibits oviposition; the reverse transfer stimulates it.
4. The upper surface of the egg chorion or egg 'cover' remains intact on the seed surface after the larva has entered the seed and continues to deter egg-laying for at least as long as the period required for larval development. 14-day-old egg covers provide as much deterrence as freshly laid eggs.     

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

Abstract.

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

     

Effects of search experience in a resource-heterogeneous environment on the oviposition decisions of the seed beetle, Callosobruchus maculatus (F.)

Abstract.  1. This study investigates how female seed beetles, Callosobruchus maculatus , distribute their eggs on various-sized seeds when the size of seed was varied during the egg-laying period.
2. Beetles were allowed to lay eggs on one of three arrays of 64 adzuki beans ( Vigna angularis ). Each array contained four size classes of seed, ranging from small (5.0–5.5 mm diameter) to large (6.5–7.0 mm), but differed in how they were distributed within the environment. In the most heterogeneous condition (the 64-patch design), the four sizes were interspersed, while in the least heterogeneous condition (the four-patch design) they were grouped into four separate blocks. Thus, a beetle exploring the 64-patch design would frequently encounter all four seed sizes, whereas a beetle exploring the four-patch design would only rarely encounter a change in bean size.
3. Beetles experiencing greater seed size heterogeneity were more likely to lay eggs on larger seeds, whereas those in the blocked condition were more likely to oviposit on small seeds. Beetle responses to seed size heterogeneity suggest that the degree of preference for large seeds depends on a female's recent experience.
4. Female beetles exhibited size discrimination throughout their egg-laying process; however, there was a trade-off between seed size and egg discrimination (i.e. avoiding those seeds already containing developing eggs) in response to the change in fitness gained from either laying on larger seeds or lower egg-load seeds during the egg-laying process.
5. Our model provides the first evidence that evolving seed size discrimination ability is adaptive for the seed beetle with egg-discrimination ability.     

Two forms of egg defence in a chrysomelid beetle: egg clumping and excrement cover

Abstract.

• 1 Field experiments demonstrated that the faecal covering that female Microrhopala vittata (Fabr.) (Coleoptera: Chrysomelidae) place over their egg masses significantly reduces egg mortality.
• 2 The bottom egg in the egg mass, which lies against the leaf of the host plant, suffers significantly higher mortality than the other eggs in the egg mass.
• 3 The parasite Chrysonotomyia sp. (Hymenoptera: Eulophidae) generally parasitizes only the bottom egg in the egg mass, while predators rarely penetrate the faecal covering.
• 4 No significant relationship was found between mortality and the number of egg masses per leaf.
• 5 By placing eggs in masses, females may ensure that at least the upper eggs in any egg mass are effectively protected against virtually all natural enemies likely to pose a threat.

     

Gender polymorphism in flowers of Silene vulgaris (Moench) Garcke (Caryophyllaceae)

Silene vulgaris occurs in Israel as a stolonifcrous tetraploid which forms mostly sexually polymorphic populations. Fully hermaphrodite and fully male-sterile plants are linked by a range of intermediate forms which are gynomonoecious and bear hermaphrodite, male-sterile, and partially male-sterile flowers. Male-sterile flowers differ from hermaphrodite ones by having a narrower calyx, a shorter corolla, a thicker style, and a considerably larger stigmatic area with longer papillae which are more markedly bulbous basally. In individual anthers of hermaphrodite flowers, diameters of stained pollen grains showed a continuous variation from 36 to 80 μm with a modal value of 56. About 30% of pollen was found to be non-stainable. Reduction in male fertility occurs at different levels, from small or inviable pollen grains through abortion of single anthers, abortion of entire androecia, and through different degrees of gynomonoecy to totally male-sterile individuals. The proportion of stainable pollen to ovules in hermaphrodite flowers alone was found to be less than 100. From the data presented, less than a third of all ovules produced in the different kinds of flower develop into seeds. This may reflect an inadequacy of pollen, which the local population of S. vulgaris can tolerate because of its stoloniferous habit.     

Effects of predation on clutch size and egg dispersion in the codling moth Laspeyresia pomonella

ABSTRACT.

• 1 The effects of predation on clutch size and egg dispersion in the codling moth Laspeyresia pomonella (L.) were experimentally studied in an orchard by recording survival of eggs glued onto different substrates.
• 2 Egg mortality due to sucking insects was readily distinguishable from that due to chewing insects.
• 3 In both the field and laboratory, females preferred to deposit eggs singly on the uppersides of leaves.
• 4 Eggs on the uppersides of leaves and on fruit survived significantly better than did those on the undersides of leaves or on twigs.
• 5 Egg losses were highest during the early part of the flight season.
• 6 The smallest (one egg) and largest (nine eggs) clutches, associated with one egg-bearing leaf per twig, both suffered the lowest rates of predation. Factors selecting against oviposition on fruits and production of large clutch sizes are presented and discussed.

     

Deterred oviposition response of Monochamus alternatus (Coleoptera: Cerambycidae) to oviposition scars occupied by eggs

1 The oviposition behaviour and response of Monochamus alternatus females to oviposition scars were investigated in the laboratory. 2 Prior to oviposition, females gnawed at the bark surface of Pinus densiflora bolts to make a wound. Then females turned their bodies 180° to position their ovipositors over the wounds and inserted them under the bark through the wounds. After an oviposition, a jelly was deposited while the ovipositor was still inserted. The females then withdrew their ovipositors and rubbed the oviposition scars with the tips of their abdomens. 3 When searching females encountered oviposition scars, they stopped walking and drummed the surface and inside of the oviposition scars with their maxillary and labial palpi. 4 Eighty-six percent of females left oviposition scars containing single eggs after the palpation. By contrast, when females encountered oviposition scars containing no eggs, 76% of them began to gnaw at the scars and 64% deposited single eggs. The response to artificial oviposition scars was similar to that to vacant oviposition scars made by the females. 5 The results of various observations and experiments showed that the females could recognize oviposition scars and discriminate the scars occupied by single eggs from vacant ones, and suggested that the palpation of oviposition scars was the critical discrimination behaviour, indicating mediation by chemical cues.     

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.     

Plasticity in the egg-spacing behavior of a seed beetle: Effects of host deprivation and seed patchiness (Coleoptera: Bruchidae)

Egg-laying females of the seed beetle Callosobruchus maculatusdiscriminate between egg-free and egg-laden seeds and produce a nearly uniform distribution of eggs among seeds. We examined plasticity in this trait in response to both an internal factor (level of host deprivation) and an environmental one (the spatial configuration of available seeds). Responses to each factor were measured in genetically divergent strains that show a relatively strong (S strain) or weak (B strain) tendency to spread eggs evenly among seeds. Following a modest (10-h) period of host deprivation, S-strain females distributed their eggs less uniformly among seeds; the proportion of females committing at least one oviposition mistake increased from 20 to 50%. Similarly, S-strain females distributed their eggs less uniformly if seeds were presented in multiple, discrete patches instead of in a single, large patch. The higher frequency of oviposition mistakes in the multiple-patch arena was caused in part by females maintaining a uniform distribution of eggs within patches but not among patches. In contrast, females from the sloppier B strain were unaffected by either host deprivation or resource dispersion. Responses to seed patchiness are discussed in relation to the role of learning in the egg-spacing behavior of C. maculatus.     

Incidence of Anagrus obscurus (Hymenoptera: Mymaridae) egg parasitism on Calopteryx haemorrhoidalis and Platycnemis pennipes (Odonata: Calopterygidae: Platycnemididae) in Italy

Very little is known about the incidence of egg parasitoids in odonates, perhaps because Odonata eggs are well protected by stems or leaves, sometimes below water. In Central Italy (Pontecorvo, Frosinone Province) two damselflies, Calopteryx haemorrhoidalis and Platycnemis pennipes, occur in high densities. In August 2007 we collected 30 stems of the aquatic plant Potamogeton sp. used as substrate for oviposition and incubated eggs in the laboratory. Most stems (24 for C. haemorrhoidalis and 23 for P. pennipes) contained Odonata eggs. Parasitoids emerged from 12 stems, with a mean parasitism of 2% for C. haemorrhoidalis and 6% for P. pennipes, and a maximum of 14% and 50%, respectively. Furthermore, we observed egg‐laying of 19 females of C. haemorrhoidalis and 11 of P. pennipes, and marked the stems where oviposition was observed. Clutches remained in the river for five days and were then collected and incubated. Parasitoids emerged from 11 of 30 stems, with an average parasitism of 8% for C. haemorrhoidalis and 3% for P. pennipes (maximums of 50% and 29%, respectively). All parasitoids belonged to the family Mymaridae, and were identified as Anagrus (Anagrus) obscurus Förster, 1861, sensu Soyka, 1955 . This is the first time that this species is described as an egg parasitoid of odonates, and that the egg parasitoid of C. haemorrhoidalis and P. pennipes is identified. Our data suggest that egg parasitism might be a significant selective factor for both odonates in the studied locality, affecting female oviposition behavior.     

Changes in egg colour, egg weight and oviposition rate with the number of eggs laid by wild females of the small heath butterfly, Coenonympha pamphilus

ABSTRACT. 1. The colour of eggs laid by individual Coenonympha pamphilus (L.) (Lep., Satyridae) females changed over their lifespan. The first laid eggs were green, but after having laid about 100 eggs, females laid only yellow eggs.
2. By following females in the field, or by capturing wild females, and noting the colour of their eggs, it was established that younger females showed higher oviposition rates and laid heavier eggs than older females.
3. Hence, wild C.pamphilus females are unable to sustain a constant egg production by extracting amino acids or any other nutrients from nectar. We hypothesize that this is a general phenomenon in nectar feeding butterflies.
4. The egg colour did not seem to match the colour of the substrate on which the female chose to deposit the egg.     

Variance in number of eggs per patch: oviposition behaviour and population dispersion in a seed parasitic moth

ABSTRACT. 1. The relationship between oviposition behaviour and population dispersion was analysed for Grey a subalba Braun (Lep., Incurvariidae), a species in which females usually, but not invariably. lay eggs in only a few schizocarps (seed-pairs) on each umbellet they visit on Lomatium dissectum (Umbelliferae). During each of four years females exhibited a constant probability of leaving an umbellet after each egg was laid. Hence, some umbellets received more eggs than others and the behaviour matched a geometric distribution of eggs among umbellets.
2. The variance in number of schizocarps attacked per umbellet by individual females did not result from females choosing schizocarps of particular sizes or avoiding schizocarps that already contained eggs or larvae. A potential, but speculative, explanation of the variance is that females distribute their eggs among umbellets in a way that maximizes unpredictability on larval dispersion to a searching parasitoid, The pattern of oviposition by Greya females fits the truncated geometric distribution that is predicted if information, as indexed by the Shannon-Wiener entropy measure, is minimized. None the less, other measures of unpredictability or minimum information are possible, and the results highlight the problem of how to identify patterns of movement that may result from selection for unpredictability to enemies.
3. In systematic surveys of the L.dissectum population during three consecutive years, virtually all plants had between 10% and 65% of their seeds attacked. Hence, the separation of oviposition bouts between umbellets and the constant probability of leaving an umbellet after each egg was laid resulted in a broad distribution of Greya attack among L.dissectum plants.     

Parasitization by Edovum puttleri (Hymenoptera: Eulophidae) in relation to host density in the field

Abstract.

• 1 The relationship between parasitization by Edovum puttleri Grissell and density of eggs of the Colorado potato beetle, Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae), was studied on two spatial scales (eggs mass and 6 m² cage).
• 2 For both scales, rates of parasitism were generally inversely related to host density for periods ranging from 2 to 8 days after parasitoid release. Thereafter, parasitism became independent of host density.
• 3 The initial inverse-density relationship and subsequent shift to density independence may result from several factors: (1) ambient temperatures, (2) the parasitoid's limited egg production, (3) differential times of exposure of egg masses to parasitoids, and/or (4) the parasitoid's patterns of host feeding and oviposition.
• 4 Although overall levels of parasitism were relatively low, total mortality of L.decemlineata eggs (including nonviable and cannibalized eggs, and those killed by parasitoid feeding) in parasitized egg masses was consistently high (?70–90%).

     

Flexible oviposition behavior in the golden egg bug (Phyllomorpha laciniata) and its implications for offspring survival

Female golden egg bugs show unique flexibility in their oviposition behavior. Females can lay eggs on plants, where they are leftunattended, or on the back of conspecifics, where they remainuntil hatching. In this article we show that eggs have greatersurvival rates when carried by an adult than when laid on plants.The main causes of egg mortality are predators and a parasitoidwasp. Our results suggest that, although predation pressureis similar, fewer eggs are attacked by parasitoid wasps whencarried by an adult than when laid on plants. In addition,we show that, when given a choice, females prefer to lay eggson the backs of conspecifics than on plants. Thus, female ovipositionchoice is adaptive and minimizes individual offspring mortality.The factors that may maintain such behavioral variation in current populations are discussed.     

Mating behavior,egg laying,and embryonic development in the South American apple snail Asolene pulchella (Ampullariidae,Caenogastropoda)

Asolene pulchella is a dioecious freshwater snail from the La Plata basin, belonging to the Ampullariidae family. Our aim was to study the reproductive biology, including mating behavior, egg laying, and embryonic development under laboratory conditions. Copulations occurred underwater and lasted 2.66?h on average. The males produce fusiform paraspermatic cells (with seven to nine flagella) in addition to euspermatic cells with a corkscrew head, straight middle piece and long flagellum. Females stored sperm for up to 169?days. The egg masses (containing 98.1 eggs on average) are deposited underwater and are composed of many gelatinous packs of 1–4 eggs; the jelly matrix presented numerous calcite microcrystals. The spheroidal egg capsules measured 2.25?mm and contained a yellowish perivitellus of rubbery consistence. The embryonic development extends for 10.8?days on average. Hatchlings measured 1.4?mm and remained on the egg mass, feeding on the jelly. They resemble miniature adults but only began to feed on senescent plant material in their third week of age and begin aerial lung respiration after 8–10?weeks. The details of the structure of the egg masses and development constitute a rich source of traits for comparative and taxonomic studies in the Ampullariidae.     

Ants as egg predators of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) in Australian cotton crops

Abstract Helicoverpa armigera is a major pest of Australian cotton crops. To assess the impact of ant predation on H. armigera populations, the behaviour of four common ant taxa was observed in cotton crops in northern New South Wales over the 1999−2000 and 2001−02 seasons. Areas of cotton were artificially stocked with H. armigera eggs prior to observation. Pheidole spp. were the most frequently observed ants within the crop canopy in 1999−2000 and took the most H. armigera eggs. Iridomyrmex spp. were more frequently observed than Pheidole spp. in 2001−02 and also took some H. armigera eggs. Neither Paratrechina spp. nor Rhytidoponera metallica (Smith) took any H. armigera eggs, although both were seen in the crop canopy. Irrigation, cultivation and insecticide application disrupted foraging ants and limited their impact on H. armigera populations.     

Flower herbivory and seed predation in Silene vulgaris (Caryophyllaceae): effects of pollination and phenology

Pollination and seed predation were studied in Silene vulgaris populations during two seasons, one with much lower pollinator abundance than the other. Among the pollinators, noctuid moths of the genus Hadena also acted as seed predators. Nectar-foraging female moths oviposited in flowers, and their larvae consumed flowers and seed capsules.
Despite a lower percentage of pollinated flowers in the year of low pollinator abundance, similar numbers of flowers set fruit in both years, because fewer flower buds and flowers were eaten by Hadena larvae during the year of low pollinator visitation. The number of seed capsules preyed upon was also lower in the year with low pollinator abundance, resulting in a higher seed set. The positive correlation between the percentage of pollinated flowers and the percentage of seed capsules destroyed was also observed when comparing flowers opening in different parts of the season.
Early flowering plant individuals had the same pollination success but suffered higher seed predation than late flowering ones. Selection for maximized pollination success through synchronous flowering, is probably the main reason for the compressed flowering period in 5. vulgaris , but the high level of predation early in the season may further increase the reproductive success of synchronous flowering individuals.