Oviposition Sites of the Cypress Seed Bug <Emphasis Type="Italic">Orsillus maculatus</Emphasis> and Response of the Egg Parasitoid <Emphasis Type="Italic">Telenomus</Emphasis> gr. <Emphasis Type="Italic">Floridanus</Emphasis>

Phytophagous insects have many strategies to escape parasitoids, for example by hiding eggs into plant tissues, but oviposition in holes made by another insect is rather scarce. The cypress seed bug Orsillus maculatus Fieber (Heteroptera: Lygaeidae) is strictly dependent on the availability of cones of Cupressus sempervirens L. to oviposit. Females lay eggs either in exit holes cut through the cone scale by emerging adults of the cypress seed chalcid, Megastigmus wachtli Seitner (Hymenoptera: Torymidae), or on the inner side of scales of partly open cones. A recently discovered egg parasitoid belonging to the genus Telenomus has been shown to attack bug eggs in both oviposition sites. In this paper we investigated the parasitoid performance according to oviposition sites. Field samplings were conducted in two evergreen cypress orchards located in the south of France. The distribution and condition of the egg patches were compared between the two locations and oviposition sites. Seed bugs preferred to oviposit in emergence holes of M. wachtli, and parasitoid performance was higher in eggs laid on cone scales. The chalcid emergence holes seemed to ensure bug eggs with enemy-free space. Oviposition site selection could be an adaptive strategy to escape parasitoid attack.     

Influence of Seed Size on Exploitation by the Rice Weevil, Sitophilus oryzae

Oviposition decisions and their fitness consequences for the seed parasite Sitophilus oryzae (L.) (Coleoptera: Curculionidae) were investigated. Female S. oryzae lay eggs inside seeds such as wheat [Triticum aestivum (L.)]. Because larvae develop to adult within a single seed, the resources available are determined by the behavior of the female parent and characteristics of the seed in which the egg was deposited. Females were demonstrated to lay more eggs in kernels 20 mg. Females initiated the chewing of oviposition holes in shriveled kernels but were less likely to oviposit in them. Progeny size increased with increasing seed size, but the probability of an adult emerging was not affected. Females accepted large kernels more quickly than small kernels and this contributed to increased oviposition in large kernels. The increase in the number of eggs per kernel appears to result from an increase in number of visits resulting in oviposition rather than an increase in the number of eggs laid during a visit.     

Imperfect oviposition decisions by the pitcher plant mosquito (Wyeomyia smithii)

Summary Wyeomyia smithii mosquitoes distribute their eggs across available oviposition sites (water-holding pitcher plant leaves) of varying quality. I experimentally examined responses to three components of site quality: conspecific larval density, larval density of the pitcher plant midge,Metriocnemus knabi, and pitcher size. Responses to larval treatments were complex and apparently suboptimal. Although mosquito larval performance is better in leaves with fewer conspecific and more midge larvae, females did not lay more eggs in such pitchers. Instead, more eggs were laid in experimental pitchers containing either midge or mosquito larvae, but fewer eggs in pitchers with neither or both. More eggs were laid in larger pitchers, which tend to accumulate more resources and dry out less often. Therefore, although the oviposition decisions made were suboptimal, they were better than random.     

Oviposition choice by the Onopordum capitulum weevil Larinus latus (Coleoptera: Curculionidae) and its effect on the survival of immature stages

Female Larinus latus lay eggs into the capitula of their Onopordum spp. host plants from the onset of capitulum development until the completion of flowering. This tight linkage between insect life-history and plant development optimised larval survival, apart from some initial asynchrony between the readiness of the females to oviposit and the suitability of the very small capitula to physically support eggs. Eggs were laid on bracts and stems of capitula or directly in the florets, when these became available. Both the location of the egg and time of oviposition influenced mortality factors such as egg and larval parasitism, egg desiccation and larval establishment. Overall, survival of eggs laid later in the season into florets was higher, although the adults that emerged were smaller. The change in choice of oviposition site that occurs at the onset of flowering, not only favours survival, but ensures more efficient resource use by the larvae. This occurs because sequential flowering of Onopordum spp. drives a sequential oviposition pattern and spreads the egg load more evenly over the available capitula, reversing a trend earlier in the season to clump eggs that were laid directly on the bracts. Other potential constraints, such as capitulum size, absolute egg density and previous egg-laying do not play a major role in determining the oviposition pattern of L. latus. Larval survival was positively correlated with capitulum size and not strongly influenced by egg density. Competition for resources only appeared to play a role in smaller capitula, and manifested itself in a reduction in the size of emerging adults rather than the death of immatures. In the absence of strong interspecific competition, the oviposition behavior of L. latus has become geared to maximising resource use for larvae (i.e. its own potential competitiveness) rather than minimising interactions with other members of the capitulum endophage guild.     

Relations of intraspecific variations in fecundity, clutch size, and oviposition frequency to the body size in three species of stoneflies, Sweltsa sp., Isoperla aizuana, and Stavsolus japonicus

Most stoneflies oviposit several times during their adult stage. In this study, the relations among oviposition frequency, the number of eggs per egg mass, and body size were examined in the chloroperlid stonefly Sweltsa sp. and two perlodid stoneflies, Isoperla aizuana and Stavsolus japonicus. It was found that larger individuals tended to oviposit more frequently than smaller ones, but the relation was significant only in Isoperla aizuana. In Sweltsa sp. and Isoperla aizuana, the number of eggs per egg mass was higher for the less-frequently ovipositing individuals than for those ovipositing more frequently, and the number of eggs per egg mass decreased with successive oviposition events. Stavsolus japonicus showed the same tendency but it was not statistically significant.     

Choices and Consequences of Oviposition by Hylemya (Delia) Sp. (Diptera: Anthomyiidae)

Hylema sp. ⁵ females oviposit on the undersides of sepals of developing buds of both Ipomopsis aggregata and Polemonium foliosissimum. Eggs deposited on the latter are significantly more likely to be fully protected by the sepal than are eggs deposited on the former. Unexposed eggs have a significantly greater likelihood of successfully developing to the larval stage than do exposed eggs. The difference in frequency of egg exposure on the two plant species can be attributed to differences in sepal morphology: I. aggregata sepals are significantly narrower than those of P. foliosissimum. The hypothesis that females preferentially oviposit on larger flowers was unconfirmed by a manipulative choice experiment. Plants differing in the size of their flowers were potted together and presented to Hylemya in arrays in the field. Flowers of the larger-flowered pair were no more likely to be oviposited on than flowers of the smaller-flowered pair. However, there were significant negative correlations between the corolla length and the percentage of flowers laid on per day at each of two sites. There was also a significant positive correlation between the corolla width and the percentage of flowers laid on at one site. Thus females appear to be using some measure of flower morphology, or a correlated trait, in making oviposition decisions. The degree to which Hylemya is making suboptimal choices between host plant species is discussed and requires further examination.     

Are gardens effective in butterfly conservation? A case study with the pipevine swallowtail, <Emphasis Type="Italic">Battus philenor</Emphasis>

Gardens with nectar sources and larval host plants have been proposed to stem the decline in butterfly abundance caused by habitat loss. However, no study has provided evidence that gardens benefit butterflies. We examined the use of natural sites and gardens in the San Francisco bay area by the butterfly, Battus philenor. We found that natural sites were more likely to attract adult B. philenor, received more oviposition, and had higher juvenile survival than gardens sites. Butterflies were more likely to be present in gardens with established populations of the host plant, Aristolochia californica, growing in the sun. Battus philenor are unlikely to visit gardens with host plants planted within the past 7 years. Gardens between the ages of 8–40 years received oviposition, but did not always support completion of larval development of B. philenor. In gardens with host plants over 40 years of age, B. philenor consistently survived from egg to the adult stage. Natural enemy induced mortality of eggs did not differ between garden and natural sites, but overall egg survival was lower in gardens than at natural sites. It is unlikely that gardens serve as 'refugia' for B. philenor in years when populations in natural sites experience low survival or low fecundity. Even in gardens capable of supporting larvae to maturity, the density of eggs and survival rates were lower than in natural populations of the host plant suggesting that gardens were not optimal habitats. Therefore, without evidence that juvenile abundance and survival rates in gardens matches or exceeds that in natural sites, it is most likely that gardens act as population sinks for B. philenor.     

Density-dependent habitat selection by brown-headed cowbirds (<Emphasis Type="Italic">Molothrus ater</Emphasis>) in tallgrass prairie

Local distributions of avian brood parasites among their host habitats may depend upon conspecific parasite density. We used isodar analysis to test for density-dependent habitat selection in brown-headed cowbirds (Molothrus ater) among tallgrass prairie adjacent to wooded edges, and prairie interior habitat (>100 m from wooded edges) with and without experimental perches. Eight study sites containing these three habitat treatments were established along a geographical gradient in cowbird abundance within the Flint Hills region of Eastern Kansas and Oklahoma, USA. The focal host species of our study, the dickcissel (Spiza americana), is the most abundant and preferred cowbird host in the prairie of this region. Cowbird relative abundance and cowbird:host abundance ratios were used as estimates of female cowbird density, whereas cowbird egg density was measured as parasitism frequency (percent of dickcissel nests parasitized), and parasitism intensity (number of cowbird eggs per parasitized nest). Geographical variation in cowbird abundance was independent of host abundance. Within study sites, host abundance was highest in wooded edge plots, intermediate in the experimental perch plots, and lowest in prairie interior. Cowbirds exhibited a pattern of density-dependent selection of prairie edge versus experimental perch and interior habitats. On sites where measures of cowbird density were lowest, all cowbird density estimates (female cowbirds and their eggs) were highest near (100 m) wooded edges, where host and perch availability are highest. However, as overall cowbird density increased geographically, these density estimates increased more rapidly in experimental perch plots and prairie interiors. Variation in cowbird abundance and cowbird:host ratios suggested density-dependent cowbird selection of experimental perch over prairie interior habitat, but parasitism levels on dickcissel nests were similar among these two habitats at all levels of local cowbird parasitism. The density-dependent pattern of cowbird distribution among prairie edge and interior suggested that density effects on perceived cowbird fitness are greatest at wooded edges. A positive relationship between daily nest mortality rates of parasitized nests during the nestling period with parasitism intensity levels per nest suggested a density-dependent effect on cowbird reproductive success. However, this relationship was similar among habitats, such that all habitats should have been perceived as being equally suitable to cowbirds at all densities. Other unmeasured effects on cowbird habitat suitability (e.g., reduced cowbird success in edge-dwelling host nests, cowbird despotism at edges) might have affected cowbird habitat selection. Managers attempting to minimize cowbird parasitism on sensitive cowbird hosts should consider that hosts in otherwise less-preferred cowbird habitats (e.g., habitat interiors) are at greater risk of being parasitized where cowbirds become particularly abundant.     

Population responses by <Emphasis Type="Italic">Orius insidiosus</Emphasis> to vegetational diversity

The abundance of different life stages of Orius insidiosus (Say) (Heteroptera: Anthocoridae) and its prey were recorded in vegetationally diverse (soybean and agronomic weeds) and monoculture (soybean only) fields. Orius insidiosus adults and nymphs were more abundant in diversified plots than in monocultures. A similar number of O. insidiosus eggs were found in the two treatments, but twice as many eggs were laid on non-crop plants than on soybeans within the vegetationally diverse plots. Prey densities were equivalent in the two treatments. In olfactometer assays, naïve O. insidiosus females were unresponsive to odors from three weed species (morning glory, redroot pigweed and velvetleaf). The current results, coupled with previous experimental observations, lead us to believe that higher abundance of O. insidiosus in vegetationally diverse habitats could be related to improved fitness of the predator, which in turn is related to certain plant qualities (e.g., nutrition, plant architecture, etc.). Proximal cues are likely more influential to oviposition decisions by O. insidiosus females than volatile signals.     

The Oviposition Behavior of the Predator Orius insidiosus: Acceptability and Preference for Different Plants

The ability of natural enemies to reproduce within cropland and effectively suppress pests depends on the presence of plants on which to oviposit within the agroecosystems. Our research investigates the acceptability and preferences of a range of plants for oviposition by the predatory bug Orius insidiosus (Say) (Hemiptera: Anthocoridae) in the laboratory. Within-plant preferences on pole beans as oviposition sites were evaluated in laboratory choice tests. The acceptability and preference of O. insidiosus females for pole bean, soybean, redroot pigweed, and velvetleaf were evaluated in choice and no-choice tests (respectively) in the laboratory. Observations on the acceptability of green foxtail, orchardgrass, buffalograss, smooth brome, redtop grass, blue grama, and tall fescue for oviposition were also conducted. O. insidiosus preferred to lay its eggs on the petiole and leaflet petioles of pole beans, and did not distinguish among nodes or petioles of different lengths. Although all broadleaved plants were suitable for egg development, the acceptability of these plants differed significantly, with pole beans being most acceptable and almost no eggs being laid on velvetleaf. Preference tests supported the results of the no-choice tests, with pole bean being the most preferred, and no eggs being laid on the velvetleaf. Green foxtail and orchardgrass were the only grass species found to be acceptable to O. insidiosus. The implications of soybean monocultures on the reproductive capacity of and biological control by O. insidiosus are discussed, as are possible mechanisms underlying the decision-making process for oviposition.     

The influence of leaf age on the oviposition preference of Chrysophtharta bimaculata (Olivier) and the establishment of neonates

1 The degree of discrimination shown by a herbivore when selecting oviposition sites has been suggested as a key factor to understanding herbivore population dynamics. Chrysophtharta bimaculata (Coleoptera: Chrysomelidae) is a primary pest of Tasmanian eucalypt forests and can cause severe defoliation. Previous work suggests that females show discrimination when selecting oviposition sites. Our aim was to test the degree of oviposition discrimination exhibited by C. bimaculata with regards to leaf toughness, a character that is critical to neonate survival. 2 We conducted an experiment examining the leaf toughness critical for neonate survival and found that significant larval mortality occurs above a toughness of 46.9 g. We also determined that the maximum toughness of leaves upon which larvae established in the field was 48.2 g, supporting the laboratory result. 3 Field surveys showed that although the majority of eggs were laid on leaves suitable for larval establishment, many eggs were laid on unsuitable, tougher leaves. However, all eggs were normally placed within 20 cm of suitable leaves and glasshouse trials demonstrated the neonates could move this distance without mortality occurring. 4 We conclude that egg batch distribution and larval performance of C. bimaculata will influence the population dynamics of C. bimaculata in two ways. Firstly, the availability of expanding/newly expanding leaves of eucalypt hosts will determine larval carrying capacity. Secondly, at a more localized level, the deposition of large numbers of egg batches on both suitable and unsuitable leaves followed by successful neonate migration increases the risk of resource depletion and poor larval development.     

Density-dependent egg dispersion in flowers of Silene vulgaris by the seed predator Hadena confusa (Noctuidae)

Abstract.

• 1 Hadena moths drink nectar from, pollinate, and oviposit into the flowers of the genus Silene. In the gynodioecious Silene vulgaris (Moench) Garcke (Caryophyllaceae), eggs were laid by Hadena confusa (Hufn.) females both in male phase flowers, which could not be pollinated by the moth at the time of oviposition, and in female phase and female flowers that allowed pollination.
• 2 Flowers in which an egg had been laid had a lowered probability of receiving a second egg laid by another female during the same night.
• 3 The degree of flower discrimination by the moth with respect to the presence of eggs was positively correlated with the proportion of flowers containing eggs.
• 4 The oviposition behaviour of H.confusa is moulded by four factors: (1) a high probability of chosen male phase flowers later becoming pollinated by other moths, (2) the presence of conspecific eggs and risk for larval competition, (3) probability of presence of conspecific eggs also in neighbouring flowers, (4) capability of larvae to move to adjacent flowers.

     

Nickel hyperaccumulation by Streptanthus polygaloides protects against the folivore Plutella xylostella (Lepidoptera: Plutellidae)

We determined the effectiveness of Ni as an elemental defence of Streptanthus polygaloides (Brassicaceae) against a crucifer specialist folivore, diamondback moth (DBM), Plutella xylostella. An oviposition experiment used arrays of S. polygaloides grown on Ni-amended (high-Ni) soil interspersed with plants grown on unamended (low-Ni) soil and eggs were allowed to hatch and larvae fed freely among plants in the arrays. We also explored oviposition preference by allowing moths to oviposit on foil sheets coated with high- or low-Ni plant extract. This was followed by an experiment using low-Ni plant extract to which varying amounts of Ni had been added and an experiment using sheets coated with sinigrin (allyl glucosinolate) as an oviposition stimulant. Diamondback moths laid 2.5-fold more eggs on low-Ni plants than on high-Ni plants and larval feeding was greater on low-Ni plants. High-Ni plants grew twice as tall, produced more leaves, and produced almost 3.5-fold more flowers. Low-Ni plants contained more allyl glucosinolate than high-Ni plants and moths preferred to oviposit on foil sheets dipped in low-Ni plant extract. Moths showed no preference when Ni concentration of low-Ni extract was varied and overwhelmingly preferred sinigrin coated sheets. We conclude that Ni hyperaccumulation is an effective elemental defence against this herbivore, increasing plant fitness through a combination of toxicity to DBM larvae and decreased oviposition by adults.     

Counterstrategy to Egg Dumping in a Coreid Bug: Recipient Individuals Discard Eggs from Their Backs

The golden egg bug, Phyllomorpha laciniata Vill. (Heteroptera: Coreidae), is the only terrestrial insect in which females oviposit on the backs of female and male conspecifics. Eggs do not survive unless carried by a bug. Herein, I report laboratory observations that egg-carrying individuals actively brush their backs against the host plant seemingly in an effort to rub off eggs. Egg scraping is more common among individuals carrying many eggs than among those carrying only a few eggs. The most recently received eggs were rubbed off first. Females did not avoid laying eggs on the backs of egg-loaded individuals, nor did bugs carrying several eggs resist oviposition attempts more often than unloaded ones. Some males were likely to have fertilized the eggs they scraped off their backs. Laboratory results of active egg removal correspond with egg loss in the field, suggesting that egg scraping may explain egg loss in nature. The data indicate a cost of egg carrying to an individual and an evolutionary arms race between oviposition and discarding behavior.     

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.     

Maternal behaviours may explain riffle‐scale variations in some stream insect populations

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The effect of prey density and host plant characteristics on oviposition and fertility in Anthocoris confusus (Reuter)

• 1 Anthocoris confusus females show the greatest egg production when fed on eight adult Aulacorthum circumflexus per day. Prey densities below six result in a marked fall off in egg production.
• 2 Low prey densities result in reduced egg fertility and a decrease in oviposition period.
• 3 A.confusus females oviposit on those parts of a broad bean plant which support the highest aphid densities. This increases the probability of survival of the emerging nymphs.
• 4 Females are also able to distinguish between young, fully turgid, plants and older, more flaccid, plants and oviposit preferentially in the younger ones. Thus the eggs develop before the plant dies.

     

Oviposition behavior of the cabbage root fly,Delia radicum (L.), influenced by host plant extracts

An ethanolic extract of cabbage leaves (Brassica oleraceavar. capitata,Golden Acre)and derived fractions were tested on natural and surrogate leaves in order to study the oviposition behavior of the cabbage root fly Delia radicum(Diptera: Anthomyiidae). On surrogate plastic leaves coated with a thin layer of paraffin wax and treated with 0.1 gram leaf equivalent (gle) of an ethanolic raw cabbage extract, the females displayed the same sequence of behavioral patterns as on a natural host plant. The quantified oviposition behavior correlated well with the actual number of eggs laid. The extract-treated surrogate leaves received at least as many eggs as natural leaves with a similar surface area. Previous exposure to surrogate or natural leaves seemed not to induce a specific preference. The three fractions (hexane, butanol, and water) of the raw extract stimulated the oviposition behavior. This was taken as evidence for the presence of a multicomponent mixture or a chemical pattern in the cabbage leaves stimulating oviposition. At the tested concentration each fraction alone could stimulate in some individuals the complete behavior. No effect of volatile components of the raw extract could be detected. This is thought to be due to the extraction procedure, which limits the production of attractive, volatile compounds, such as isothiocyanates.     

Egg-laying by the speckled wood butterfly (Pararge aegeria): the role of female behaviour, host plant abundance and temperature

ABSTRACT.

• 1 Egg-laying by Pararge aegeria (L.) was studied in relation to host plant abundance, temperature and behaviour in one woodland site in central England.
• 2 Eggs were laid on the undersides of leaves of fifteen of thirty-one species of grass located in the study site. Most were deposited singly although on several occasions a number of females laid on a single leaf.
• 3 There was no clear relationship between host plant abundance and host plant use, the species used being widespread and abundant.
• 4 Most eggs were laid on plants within the temperature range 24–30°C. In spring and later summer these sites were in sunlit open areas but in midsummer they were in the woodland ground layer.
• 5 Females distributed their eggs over a large area, usually making a dispersal flight after laying an egg.

     

A test of the preference–performance hypothesis with stream insects: selective oviposition affects the hatching success of caddisfly eggs

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