Searching at different spatial scales: the foraging behaviour of the aphid parasitoid Aphidius rosae in rose bushes

The searching patterns of the aphid parasitoid Aphidius rosae were analysed at three different spatial scales: leaves, shoots and bushes. Parasitoid females searched aphid-infested leaves and shoots intensively and remained on average more than twice as long on infested than on uninfested shoots. Patch times and oviposition numbers per shoot were highly variable both between females and for different shoot visits within females. However, at the shoot and bush level low oviposition numbers were generally found. The time spent on different behavioural patterns (searching, resting, feeding, host handling) changed significantly during subsequent shoot visits of individual females but oviposition success was not influenced by this change. Parasitoids searched individual leaves and shoots mainly by walking, while moving between shoots occurred exclusively by flight. The travel time between shoots (i.e. flight time) accounted for less than 1% of the residence time in a bush. At the bush level foraging was characterized by a high ability to localize infested shoots and consequently little time was wasted in searching on uninfested shoots. The pattern of resource exploitation of individual females was consistent with the distribution of A. rosae larvae in field samples taken from individual rose bushes.     

Nocturnal activity and resource utilization in the aphid hyperparasitoid, Dendrocerus carpenteri

Abstract.

• 1 Females of the aphid hyperparasitoid Dendrocerus carpenteri (Curtis) search successfully for hosts during both day and night. Oviposition numbers per host patch did not differ significantly between day and night.
• 2 D.carpenteri females also displayed a nocturnal flight activity, showing that they are not only capable of searching on a given host plant but also of dispersing between host plants.
• 3 Nocturnal oviposition activity was mainly influenced by egg load. Females with a high egg load laid more eggs at night than females with a comparatively low egg load. Thus, D.carpenteri females may use nocturnal foraging to compensate for the lack of oviposition opportunities during day.
• 4 D.carpenteri females which foraged continuously for hosts both day and night (= for 24 h per day) benefitted from an 1.4-fold increase in lifetime reproductive success when compared to females which foraged only by day (= for 16 h per day).
• 5 The benefit of night foraging for this species is a significantly increased reproductive success.

     

Oviposition Site Selection by the Regal Fritillary, Speyeria idalia, as Affected by Proximity of Violet Host Plants

Selection of oviposition sites by female regal fritillary butterflies, Speyeria idalia (Drury), in relation to the location and abundance of their larval food plant, Viola pedatifida G. Don, was studied in Kansas tallgrass prairie. To identify potential cues that females use to select oviposition microsites, we compared plots in which eggs were laid with paired control plots in terms of violet abundance, distance from plot center to the nearest violet plant, plant species composition and relative abundance, plant diversity (Shannon's index), and average plant canopy height. No significant differences occurred between control and oviposition sites for any of these variables (P > 0.15). Violets were present in only 30% of the 1-m-diameter oviposition plots, compared with 24% of the corresponding controls. Furthermore, eggs were never laid directly on violets even when they were present nearby. These data imply that S. idalia females do not preferentially orient to or oviposit on their larval food plant. Nevertheless, female S. idalia did not oviposit randomly, for they invariably chose microsites near the ground that were shaded by the grass/forb overstory and usually deposited eggs on the underside of dead vegetation. We speculate that environmental stresses such as high temperatures and intense solar insolation during the egg stage or harsh overwintering conditions experienced by first-instar larvae impact survival and influence choice of oviposition sites. High fecundity (more than 2000 eggs in some individuals) may allow this species to use a conditional, sweepstakes strategy, i.e., producing and spreading many eggs over prairie that harbors host plants to compensate for low egg and larval survivorship.     

Studies on ticks of veterinary importance in Nigeria XII. Oviposition and eclosion in five species of IXODID ticks in contrasting habitats

The preoviposition and oviposition periods, the eclosion periods and numbers of eggs laid by adult ticks of five species, namelyAmblyomma variegatum, Boophilus decoloratus, B. geigyi, Hyalomma rufipes andH. truncatum, maintained in a natural habitat were compared with those maintained in semi-natural and artificial habitats. Within the natural habitats, open and shady sites were distinguished.Maximum oviposition occurred during the peak of the rains in engorgedA. variegatum andB. decoloratus, and the numbers of eggs laid by those kept in the natural and semi-natural habitats were significantly lower in the dry season than in the rainy season. Maximum oviposition in engorgedH. rufipes kept in the natural habitat occurred during the early rains while minimum oviposition took place during the peak of the rains.Oviposition in engorgedH. truncatum was poor among those kept in the natural habitat during the peak and end of the rains. EngorgedA. variegatum andB. decoloratus kept in shady sites of the natural habitat laid significantly more eggs than in all other habitats at all seasons, while forH. truncatum andH. rufipes, numbers of eggs laid in the open site were significantly higher than those laid in other habitats at all seasons.In all species investigated, success in oviposition was aided by moisture provided by light to moderate rainfall, while excessive moisture in terms of heavy rainfall adversely affected oviposition.     

Host-searching behavior ofVenturia canescens (Grav.) (Hymenoptera: Ichneumonidae): Interference—the effect of mature egg load and prior behavior

The foraging behavior ofVenturia canescens, a solitary endoparasitoid of lepidopteran larvae, was investigated in the laboratory. Females with a greater number of mature eggs in their ovarioles and oviducts parasitized a greater number of hosts and won a greater proportion of encounters with other searching females. Wasps which had been exposed to hosts prior to an experimental trial lost a higher proportion ofagonistic encounters with conspecifics than wasps which had no prior exposure to hosts. The behavior of a wasp at the time of the encounter influenced the outcome of the encounter. Wasps involved in active search of the host medium with the ovipositor (probing) were more likely to win encounters than wasps in any other behavioral category. In a situation where the agonistic encounter was between two probing wasps, both contestants were equally likely to win. Results are discussed in the light of the idea that mutual interference arises, in this species, as a result of agonistic encounters between searching females and recent dynamic-programming models which suggest that parasitoid oviposition should be influenced by mature egg load.     

The Predatory Mite Phytoseiulus persimilis Adjusts Patch-leaving to Own and Progeny Prey Needs

Integration of optimal foraging and optimal oviposition theories suggests that predator females should adjust patch leaving to own and progeny prey needs to maximize current and future reproductive success. We tested this hypothesis in the predatory mite Phytoseiulus persimilis and its patchily distributed prey, the two-spotted spider mite Tetranychus urticae. In three separate experiments we assessed (1) the minimum number of prey needed to complete juvenile development, (2) the minimum number of prey needed to produce an egg, and (3) the ratio between eggs laid and spider mites left when a gravid P. persimilis female leaves a patch. Experiments (1) and (2) were the pre-requirements to assess the fitness costs associated with staying or leaving a prey patch. Immature P. persimilis needed at least 7 and on average 14±3.6 (SD) T. urticae eggs to reach adulthood. Gravid females needed at least 5 and on average 8.5±3.1 (SD) T. urticae eggs to produce an egg. Most females left the initial patch before spider mite extinction, leaving prey for progeny to develop to adulthood. Females placed in a low density patch left 5.6±6.1 (SD) eggs per egg laid, whereas those placed in a high density patch left 15.8±13.7 (SD) eggs per egg laid. The three experiments in concert suggest that gravid P. persimilis females are able to balance the trade off between optimal foraging and optimal oviposition and adjust patch-leaving to own and progeny prey needs.     

Helicoverpa armigera (Hübner): can wheat stubble protect cotton plants against attack?

Abstract  When investigating strategies for Helicoverpa armigera (Hübner) control, it is important to understand oviposition behaviour. Cotton ( Gossypium hirsutum ) was sown into standing wheat ( Triticum astivum L.) stubble in a closed arena to investigate the effect of stubble on H. armigera moth behaviour and oviposition. Infrared cameras were used to track moths and determine whether stubble acted as a physical barrier or provided camouflage to cotton plants, thereby reducing oviposition. Searching activity was observed to peak shortly before dawn (03:00 and 04:00 h) and remained high until just after dawn (4 h window). Moths spent more time resting on cotton plants than spiralling above them, and the least time flying across the arena. While female moths spent more time searching for cotton plants growing in wheat stubble, the difference in oviposition was not significant. As similar numbers of eggs were laid on cotton plants with stubble (3.5/plant SE ±0.87) and without stubble (2.5/plant SE ±0.91), wheat stubble does not appear to provide camouflage to cotton plants. There was no significant difference in the location of eggs deposited on cotton plants with and without stubble, although more eggs were laid on the tops of cotton leaves in wheat stubble. As the spatial and temporal distribution of eggs laid on the cotton plant is a crucial component of population stability, eggs laid on the upper side of leaves on cotton plants may be more prone to fatalities caused by environmental factors such as wind and rain. Therefore, although stubble did not influence the number of eggs laid, it did affect their distribution on the plant, which may result in increased mortality of eggs on cotton plants sown into standing wheat stubble.     

Oviposition behaviour and response of Monochamus scutellatus (Coleoptera: Cerambycidae) to conspecific eggs and larvae

• 1 The oviposition behaviour of white‐spotted sawyer beetle Monochamus scutellatus (Say) (Coleoptera: Cerambycidae) females was studied under laboratory and field conditions.
• 2 Females walked over the bark surface and stopped to palpate it with their labial and maxillary palpi. Once a potential oviposition site was located, the female excavated a scar in the bark with her mandibles, deposited an egg and brown plug in the scar and inserted her mandibles again into the scar prior to leaving the area.
• 3 Female M. scutellatus preferred to lay eggs on bolts containing no eggs (control) to those containing eggs from other females, but did not show this preference when provided with control bolts and those containing their own eggs. When females were provided with bolts containing their own eggs and bolts containing eggs from other females, they laid more eggs on bolts containing their own eggs. Females laid more eggs on control bolts than on bolts containing their own larvae or larvae from other females.
• 4 The brown plug in the oviposition scar may provide a protective barrier to the egg, a chemical message that the site is occupied, or both.

     

Temporal change in the location of egg-laying by a bud-galling sawfly,Euura mucronata,on growing shoots of Salix cinerea

Summary Temporal change in the egg-laying behaviour of Euura mucronata was studied on growing shoots of Salix cinerea. Many new shoots arise from each previous year's shoot of S. cinerea; they grow very rapidly at the beginning of the oviposition period of E. mucronata, but their growth pattern changes dramatically during the 3 weeks of oviposition. When oviposition commences, all new shoots are equally long, and E. mucronata females lay eggs on them randomly; but toward the end of oviposition, eggs are laid on the longest of the new shoots, which originate on the distal part of the previous year's shoot. By the end of oviposition, the mean proportion of ovipositor borings that had resulted in egg-laying was 65.8% on distal shoots and declined linearly to 25% on shoots arising from the base of the previous year's shoot. The proportion of attacked buds from which larvae emerged declined non-linearly from 13.8% on the distal shoot to 3.5% on the basal shoots. The position of the shoot accounted for 67% and 73% of the variance in success of egg-laying and larval development, respectively.     

Sex differences in foraging behaviour and oviposition site preference in an insect predator, Orius sauteri

The effects of patch quality on the foraging behaviour of an anthocorid predator Orius sauteri (Poppius) were compared between sexes. Prior experience in patches was also studied to determine whether this was a factor affecting oviposition decisions. Patch quality affected patch residence time differently for the two sexes; females stayed much longer in a patch with prey (60 Thrips palmi larvae) than a patch without prey, while males did not remain in any patch for extended periods. Most of the females remained in or moved to patches with prey, whereas males dispersed, irrespective of patch quality. Both females released in patches with prey and females released in patches without prey deposited more eggs per hour in patches with prey than in patches without prey. Females released in patches without prey laid eggs in patches with prey at higher rates than did females released in patches with prey. Causes for the sex difference in patch residence time and allocation are discussed in relation to optimal foraging theory. The significance of selective oviposition and the role of experience in oviposition decisions within heterogeneous environments are also discussed.     

Maternal effect determines drought resistance of eggs in the predatory mite Phytoseiulus persimilis

The ability of an organism to adapt to short-term environmental changes within its lifetime is of fundamental importance. This adaptation may occur through phenotypic plasticity. Insects and mites, in particular, are sensitive to changes in temperature and humidity, especially during the juvenile stages. We studied the role of phenotypic plasticity in the adaptation of eggs to different relative humidity conditions, in the predatory mite Phytoseiulus persimilis, used worldwide as a biological control agent of the spider mite Tetranychus urticae. The biocontrol efficacy of P. persimilis decreases under dry conditions, partly because P. persimilis eggs are sensitive to drought. We exposed P. persimilis adult females from two different strains to constant and variable humidity regimes and evaluated the hatching rate of their eggs in dry conditions, as well as the survival and oviposition rates of these females. Whereas the eggs laid by P. persimilis females exposed to constant high humidity did not survive in dry conditions, females exposed to constant low humidity started laying drought-resistant eggs after 24 h of exposure. Survival and oviposition rates of the females were affected by humidity: females laid fewer eggs under constant low humidity and had a shorter lifespan under constant high and constant low humidity. The humidity regimes tested had similar effects across the two P. persimilis strains. Our results demonstrate that transgenerational phenotypic plasticity, called maternal effect, allows P. persimilis females to prepare their offspring for dry conditions.     

Field oviposition rates and egg load dynamics of pollen beetles (Meligethes aeneus Fab.) (Colepotera: Nitidulidae)

Abstract 1 Egg loads from field collected pollen beetles (Meligethes aeneus Fab., Coleoptera: Nitidulidae) were determined by dissecting beetles caught at the beginning and end of the putative daily oviposition period. Field collected beetles were offered Brassica napus (L.) plants in cages for 8 (morning and early afternoon), 16 (overnight), and 24 h to ascertain the number of eggs laid during these time periods. 2 Most eggs were laid in the morning and early afternoon. The proportion of gravid females was higher at the beginning of the oviposition period than at the end. Most females in the morning carried two eggs, whereas one egg was more common in the afternoon. 3 We hypothesized that the number of eggs laid during the oviposition period would be equivalent to the difference between egg loads at the beginning and end of oviposition. This was not the case; differences in egg loads were significantly lower than number of eggs laid. However, the number of eggs laid was equivalent to the egg load at the beginning of the oviposition period, suggesting that eggs available in the morning are laid during the following day. 4 Population estimates of daily oviposition rates, approximately 0.7 eggs per beetle and day, were close to estimates from laboratory studies when the proportion of gravid females was taken into consideration.     

Mixed oviposition in individual females of Gryllus firmus: Graded proportions of fast-developing and diapause eggs

Summary Eggs of field crickets (Gryllus spp.) held at 25±1°C hatch in 2–4 weeks (fast-developing eggs) or 5–28 weeks (diapause eggs). Most species lay but one type: at least 10 species lay only fast-developing eggs, and pennsylvanicus and ovisopis lay only diapause eggs. Gryllus firmus from Gainesville, Florida, lays both types, and individual females do so for as long as 8 weeks. The proportion of diapause eggs laid weekly by captive females exposed to outdoor photoperiods and temperatures varies seasonally from <5% (March–June) to ca. 50% (November–December). At outdoor temperatures in late fall some eggs that are presumptively fast-developing (at 25° C) enter diapause.Some firmus from Carolina Beach, North Carolina, lay both diapause and fast-developing eggs. Outdoor rearing experiments established that spring adults could result from fast-developing eggs of fall adults, refuting the hypothesis that spring and fall adults at that locality represent temporally isolated demes.High variance in hatching times for eggs laid by one female is appropriate to the unpredictable extremes of moisture and temperature that occur in the open, sandy habitats of G. firmus. Physiological mechanisms of the mixed oviposition and specific environmental determinants of the varying proportions are unknown.     

Quantitative studies on the eggs of Simulium (Simulium) ornatum Meigen and Simulium (Wilhelmia) equinum L. in a chalk stream in southern England

Abstract.

• 1 The egg masses of Simulium ornatum, S.equinum and S.vernum are described and information is given on numbers of eggs per egg mass and the size and number of batches laid by individual females.
• 2 The oviposition sites were studied in relation to water velocity, wind speed and direction.
• 3 The incubation periods at different river temperatures and the effects of desiccation on percentage hatch and incubation times were investigated.
• 4 The numbers of eggs laid were assessed for the winter generations of S. ornatum and S.equinum. The relevance of these to the overall production estimates is discussed

     

Impact of mating status on egg-laying and superparasitism behaviour in a parasitoid wasp

Most parasitoid female wasps can distinguish between unparasitized and parasitized hosts and use this information to optimize their progeny and sex allocation. In this study, we explored the impact of mating on oviposition behaviour (parasitism and self‐ and conspecific superparasitism) on both unparasitized and already parasitized hosts in the solitary parasitoid wasp Eupelmus vuilleti (Crw.) (Hymenoptera: Eupelmidae). Virgin and mated females had the same oviposition behaviour and laid eggs preferentially on unparasitized hosts. The sex ratio (as the proportion of females) of eggs laid by mated females in parasitism and conspecific superparasitism was 0.67 ± 0.04 and 0.57 ± 0.09, respectively. Likewise, females laid more eggs in conspecific superparasitism than self‐superparasitism under our experimental conditions. These experiments demonstrate that E. vuilleti females can (i) discriminate between unparasitized and parasitized hosts and adapt the number of eggs they lay accordingly, and (ii) probably discriminate self from conspecific superparasitized hosts. Finally, mating does not appear to influence the host discrimination capacity, the ovarian function, or the oviposition behaviour.     

Reproductive bionomics of the soft tick, Ornithodoros turicata (Acari: Argasidae)

The effects of different temperatures and relative humidities (RHs) were tested on various reproductive parameters of Ornithodoros turicata, an argasid tick that inhabits gopher tortoise burrows in Florida, USA. The pre-oviposition, oviposition and incubation periods of the ticks decreased as temperature increased. These periods were also affected by the RH. The number of eggs oviposited was affected significantly by the combined effect of temperature and RH. Fewer eggs were laid by ticks in the 24°C regimes and the 27°C/95%RH regime compared to those in the other temperature/RH groups. There was an inverse relationship between the number of eggs oviposited and the percentage of hatched larvae that was correlated with the temperature and RH. Ticks reared at 27°C/90%RH and 30°C/90%RH laid more eggs than those reared in the other combinations of temperature and humidity but fewer larvae hatched from these eggs. The reproductive fitness index (RFI) values were highest in females held in the 24°C groups and the 30°C/95%RH group, although significantly more larvae hatched at the lower temperatures. The optimum reproductive conditions for O. turicata under laboratory conditions appear to be 24°C and 90–95%RH. While mating occurred at all temperatures, none of the females laid eggs at 22°C. The ticks may move preferentially to low temperatures when not feeding to remain above the critical equilibrium humidity and/or below the critical metabolic level necessary for prolonged survival. However, most female ticks oviposited after 45 days when moved to 27°C/95%RH. Ornithodoros turicata females may have a limited capability to delay oviposition until an optimal microenvironment for egg deposition can be located in the burrow.     

Oviposition of resistant and susceptible strains of Drosophila melanogaster in the presence of deltamethrin

Oviposition of three strains of Drosophila melanogaster in the presence of deltamethrin was observed. These strains had different levels of physiological susceptibility to deltamethrin. Two-choice tests were conducted with couples of flies in petri-dish arenas containing two oviposition dishes. On the first day of the experiment, females were given a choice between a treated oviposition dish and an untreated control dish. On the second day of the experiment, two control oviposition dishes were given to females. Although individual females showed a tendency to aggregate their eggs in one of the dishes, control experiments demonstrated an overall equal distribution of eggs between the dishes. When one of the two oviposition dishes in the arena was treated with deltamethrin, the percentage of females ovipositing and the mean number of eggs laid by females were reduced, compared with control arenas. Females avoided the treated oviposition dish and laid significantly more eggs on the control dish. Furthermore, when the deltamethrin concentration was increased on the first day, female flies postponed their oviposition and laid significantly more eggs on the second day. The resistant strain, SR, demonstrated the same capacity to select the untreated site for oviposition as the susceptible strain, but it showed a smaller oviposition reduction and egg retention. The relationship between physiological and behavioural susceptibility to deltamethrin is discussed.     

Reproductive Behavior of the Bug <Emphasis Type="Italic">Molipteryx fuliginosa</Emphasis> Uhler (Heteroptera,Coreidae) in the South of the Russian Far East

Reproductive behavior of Molipteryx fuliginosa (Uhler) was investigated in Primorskii Territory of Russia. From 4 to 18 repeated copulations of one female lasting from 2 to 48 hours were recorded in cages. The behavior of ovipositing females and the stages of oviposition are described for the first time. The number of eggs laid between copulations varied from 1 to 13, the number of oviposition acts, from 4 to 11, and the total female fecundity, from 21 to 38 eggs. Caged females laid eggs on plants and also on dead substrates unsuitable for nymphal feeding, such as cloth, dry branches, and a wooden pole. Copulation of M. fuliginosa was also observed under natural conditions. The preferred mating places of M. fuliginosa in anthropogenically modified habitats and in small-leaved riparian forests were plants of Rubus idaeus L., R. caesius L., and Rubus sp. After mating, females migrated in search of places for oviposition. Single eggs were found on the following plants not known previously as hosts of this bug: Solanum lycopersicum L., Carex sp., Elytrigia repens (L.) Nevski, and Taraxacum officinale Wigg. The females seemed to lack selectivity in the choice of place for oviposition, which was not always associated with host plants, despite their abundance and availability.     

Diamondback moth egg susceptibility to rainfall: effects of host plant and oviposition behavior

Oviposition patterns of the diamondback moth (DBM), Plutella xylostella L. (Lepidoptera: Plutellidae), differ between common cabbage (Brassica oleracea L. var. capitata) and Chinese cabbage (Brassica rapa L. var. pekinensis) (Brassicaceae) host plants. This study shows that the moth prefers to oviposit on adaxial rather than abaxial leaf surfaces and petioles of both host plants. More eggs were laid in leaf veins than on leaf laminas of both host plants, especially in Chinese cabbage, where 94.6% of eggs were laid in veins. On Chinese cabbage, very few eggs were laid in clusters (≥2 eggs), whereas on common cabbage approximately 30% of eggs were laid in groups of 2 or more eggs. Removal of wax from common cabbage leaves dramatically increased the number of eggs laid singly on the leaf lamina of treated plants, suggesting that leaf waxes affect how eggs are distributed by ovipositing DBM. Eggs were most susceptible to removal by rainfall from the plant surface immediately (<1 h) after oviposition and when close to hatching (>72h old) whereas they were least susceptible 24 h after oviposition. Eggs laid on common cabbage plants were more susceptible to simulated rainfall than eggs laid on Chinese cabbage plants. On common cabbage plants, egg susceptibility to rainfall on different plant parts ranked adaxial leaf surfaces>petioles = abaxial leaf surfaces>stem, but there was no difference in egg susceptibility to rainfall on the various plant parts of Chinese cabbage. Furthermore, on common cabbage plants, eggs laid on both adaxial and abaxial leaf surfaces were afforded significant protection from the effects of rainfall by leaves higher in the plant canopy. On common cabbage plants, oviposition patterns reduce the potential impact of rainfall on eggs, possibly reducing the effect of this important abiotic mortality factor in the field.     

Do Golden Egg Bugs (Phyllomorpha laciniata: Heteroptera, Coreidae) Require Conspecifics for Oviposition?

Golden egg bug (Phyllomorpha laciniata) females lay eggs on the bodies of conspecifics of both sexes. We investigated to what extent reproduction depended on the availability of conspecifics as oviposition substrate and the acceptability of the host plant as an alternative oviposition substrate in the absence of conspecifics. Mated females were placed in experimental enclosures each containing a sprig of fresh host plant. Each experimental female was subjected to one of three treatments: isolated from conspecifics (solitary), paired with another female, or paired with a male. Solitary females laid a few eggs on the host plant but then stopped laying eggs, and solitary females laid significantly fewer eggs than those enclosed with another female or a male. Females enclosed with a male laid no more eggs than those enclosed with a female. When two previously isolated females were later enclosed together, they soon renewed oviposition. Females in nature contained significantly more oviducal eggs than did females that were enclosed with other females for a short period. Thus the availability of suitable conspecifics as oviposition substrate stimulates the deposition of mature eggs, and reproduction depends on the presence of conspecifics of either sex as oviposition substrate.