Micro‐climate determines oviposition site selection and abundance in the butterfly Pyrgus armoricanus at its northern range margin

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Conditioning of leaf-shape discrimination by chemical cues in the butterfly,Battus philenor

In a large outdoor screened enclosure, female pipevine swallowtail butterflies (Battus philenor) were trained to search selectively for leaves of a shape similar to that of the Aristolochia host species to which they were exposed as adults. Conditioning was reversed by exposure to an alternative host species with a different leaf shape. Results indicated that contact with a host plant without oviposition was sufficient to induce a change in alighting responses to leaves of different shapes. Enclosure assays employing non-host species possessing leaves of different shapes and treated with host extracts demonstrated that females associate the shape of their alighting substrate with host chemicals present on the surface of that substrate. Results suggested that contact with host extracts without oviposition can induce changes in alighting responses to leaves of different shapes. A hypothesis is presented in which the primary host species for which females in an east Texas population learn to search varies seasonally with changes in host leaf chemistry.     

Specialist pollinating seed predator exhibits oviposition strategy consistent with optimal oviposition theory

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INTERPOPULATION DIFFERENCES IN HOST PREFERENCE AND THE EVOLUTION OF LEARNING IN THE BUTTERFLY,BATTUS PHILENOR

The host-discrimination behavior of the adult female pipevine swallowtail butterfly (Battus philenor) was investigated for two populations, an east Texas population that uses two host species with different leaf shapes and a Virginia montane population that uses one host species with a single leaf shape. While Texas and Virginia females exhibited similar chemotactile responses after landing on various host species, butterflies from each population landed more frequently on certain host species used by that particular population. Despite this difference in searching behavior, Texas and Virginia populations were equally capable of learning to search for the leaf shape of a particular host species in artificial enclosure arrays. In addition, learning of leaf-shape preference was confounded equally when each population was introduced into arrays containing all the host species found in both populations. The lack of differentiation in learning of leaf-shape preference between populations that differ in host breadth and host preference argues against the specific hypothesis that learning of leaf-shape preference represents a local adaptation that permits foraging butterflies in the east Texas population to respond to seasonal changes in the relative quality or abundance of host species that differ in leaf shape. Three hypotheses are proposed to explain the apparent absence of interpopulation genetic variation in learning traits. One hypothesis supposes that learning of leaf-shape discrimination is mediated by the same physiological mechanisms that permit females to learn to discriminate among suitable and unsuitable conspecific plants. Selection for restriction of learning of leaf-shape preference in the Virginia montane population may therefore be constrained by selection for learning of other types of discrimination behavior.     

Anatomical inferences on aerial bud protection of three Eugenia shrub species from the Cerrado

• Location and degree of protection of aerial buds are important functional traits in disturbance- or stress-prone environments since aerial buds ensure the development of new organs under favourable growing conditions. This study was carried out in a Brazilian Cerrado area under regeneration after long-term Pinus cultivation, where the trees were clear-cut in 2012 and the remaining material was burned in 2014.
• After the fire treatment, several species resprouted from belowground organs and their aboveground organs were directly exposed to full sunlight. We collected 15 terminal branches with fully expanded leaves from three individuals of each of three Eugenia species to investigate if those with well-developed belowground organs invest in bark for aboveground bud protection. The samples were analysed using light and electron microscopy.
• In addition to terminal and axillary buds, all species presented accessory buds, and the number varied according to the node analysed. None of the aerial buds were protected by bark, but all were well protected by cataphylls and densely pubescent leaf primordia. There were also inter- and intra-petiolar colleters that released a mucilaginous protein exudate. The distance between the shoot apical meristem and the outer surface was longer in the terminal bud than in axillary buds. The bud leaf primordia covering the shoot apical meristem had a thick cuticle, unicellular non-glandular trichomes that accumulate phenolic and lipophilic compounds, and secretory cavities.
• Our study shows that all three Eugenia species studied here had highly protected aerial buds allocated from belowground organs. These morphological traits may improve the chances of the species' persistence in areas subjected to frost events, low relative humidity, high irradiance and harmful UV levels.

     

Evidence for an oviposition-deterring pheromone in Tephritis bardanae (Schrank) (Diptera: Tephritidae)

Summary Female Tephritis bardanae (Schrank) exhibit a characteristic ovipositor-dragging behaviour immediately after laying eggs into a flowerbud of Arctium minus (Hill) Bernh. To establish whether this behaviour is associated with an oviposition-deterring pheromone (ODP), female T. bardanae were presented with clean, unattacked flowerbuds and fly activity was monitored using video recording equipment. The distribution of oviposition and fly behaviour were analysed. Avoidance of attacked buds was revealed by the oviposition pattern becoming overdispersed. Spacing out of eggs continued until, on average, each bud contained one egg-batch, after which the distribution became more random or clumped. Analysis of fly behaviour showed that attacked and unattacked buds received similar numbers of visits, but fewer oviposition attempts were made on attacked buds. This behaviour was consistent with use of a contact pheromone deterring repeated oviposition and applied to the bud surface during ovipositor-dragging. Avoidance of attacked buds should increase the efficiency of resource use by T. bardanae populations in the field; however, distributions of egg-batches in flowerhead samples collected from Monks Wood NNR, Cambridgeshire, during 1983–1985, were highly clumped and did not provide supportive evidence. This suggests that the effectiveness of oviposition deterrence in the field is reduced, because the active life of ODP under natural conditions is short, and/or because wild females frequently experience high oviposition drive due to scarcity of suitable flowerbuds.     

Extreme weather change and the dynamics of oviposition behavior in the pipevine swallowtail, <Emphasis Type="Italic">Battus philenor</Emphasis>

Prospects of global increases in extreme weather change provide incentive to examine how such change influences animal behavior, for example, behavior associated with resource use. In this study, we examined how oviposition behavior in a southern Arizona population of pipevine swallowtails (Battus philenor L.) responded to changes in their Aristolochia host resource and vegetative background caused by the North American monsoon system. Summer monsoon rains resulted in a flush of non-host vegetation and a more than doubling in rate of landings by host-searching females on non-host vegetation. Rates of discovery of the host species A. watsoni Woot. Standl. decreased by 50% after monsoon rains. Rains did not alter host density appreciably, but resulted in significant increases in host plant size and new growth, two indicators of host suitability for B. philenor larvae. After the rains, mean clutch size on individual host plants increased by a factor of 2.5; the mean proportion of host plants encountered on which a female laid eggs also increased significantly. Females were discriminating about the host plants on which they laid eggs after alightment; plants accepted for oviposition were larger, bore more new growth, and bore fewer larvae than rejected plants. Contrary to predictions from foraging theory, degree of discrimination did not change seasonally. Finally, the rate at which eggs were laid increased seasonally, suggesting that oviposition rates were limited more before monsoon rains by the relatively low quality of hosts than they were after the rains by the relatively low rate at which hosts were found. This latter result suggests that, while butterflies possess behavioral flexibility to respond to extreme weather change, such flexibility may have limits. In particular, expected increases in the severity and frequency of droughts may result in reduced oviposition rates, reductions that could have adverse demographic consequences.     

Gregarious Oviposition and Clutch Size Adjustment by a Heliconius Butterfly1

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

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.

     

Influence of background on host-plant selection and subsequent oviposition by the cabbage root fly (Delia radicum)

The behaviour of female cabbage root flies during host plant selection was studied in the laboratory using brassica plants growing in backgrounds of bare soil, clover, grass, peas and four non-living materials. Gravid females landed about twice as often on brassica plants growing in bare soil than on comparable plants growing amongst non-host plants. Once a receptive female landed on a brassica plant, the female made, on average, four ‘spiral flights’ and two jumps on and off the plant before laying alongside the plant. Surrounding a brassica plant with a diverse background altered the behaviour of the flies, so that the spiral flights around the host plant were replaced by short hops between nearby vertical objects. The loss of contact and recontact with the host plant then prevented the females from accumulating sufficient contacts with the host plant to be stimulated to lay. Spiral flights around host plants appear to determine whether or not flies will lay alongside host plants. Flies in mixed plantings have a reduced rate of settling on the host plant, and a higher rate of locomotion, because they land frequently on non-host plants. Hence, visual stimuli appeared to have greater effects than, chemical or mechanical barriers in deterring flies from laying alongside brassica plants in diverse backgrounds. In ‘choice’ situations, backgrounds of real plants reduced oviposition alongside brassica plants by at least 50%. In ‘no-choice’ situations, flies laid similar numbers of eggs alongside all brassica plants irrespective of plant background or plant size. If numbers of fly eggs are to be reduced on commercial brassica crops by undersowing the crops with clover, plants growing in bare soil may also have to be included to provide the flies with sites preferred for oviposition.     

Influence of habitat pattern on orientation during host fruit location in the tomato fruit fly, Neoceratitis cyanescens

Fruit flies have evolved mechanisms using olfactory and visual signals to find and recognize suitable host plants. The objective of the present study was to determine how habitat patterns may assist fruit flies in locating host plants and fruit. The tomato fruit fly, Neoceratitis cyanescens (Bezzi), was chosen as an example of a specialized fruit fly, attacking plants of the Solanaceae family. A series of experiments was conducted in an outdoor field cage wherein flies were released and captured on sticky orange and yellow spheres displayed in pairs within or above potted host or non-host plants. Bright orange spheres mimicking host fruit were significantly more attractive than yellow spheres only when placed within the canopy of host plants and not when either within non-host plants or above both types of plants. Additional experiments combining sets of host and non-host plants in the same cage, or spraying leaf extract of host plant (bug weed) on non-host plants showed that volatile cues emitted by the foliage of host plants may influence the visual response of flies in attracting mature females engaged in a searching behaviour for a laying site and in assisting them to find the host fruit. Moreover, the response was specific to mature females with a high oviposition drive because starved mature females, immature females and males showed no significant preference for orange spheres. Olfactory signals emitted by the host foliage could be an indicator of an appropriate habitat, leading flies to engage in searching for a visual image.     

Reduction of oviposition time and enhanced larval feeding: two potential benefits of aggregative oviposition for the viburnum leaf beetle

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Contact chemoreception related to host selection and oviposition behaviour in the monarch butterfly, Danaus plexippus

Abstract. Behavioural events during host selection by ovipositing monarch butterflies (Danaus plexippus (L.), Danainae, Nymphalidae) include tapping the leaf surface with fore-tarsi and touching this surface with mid-tarsi (‘drumming’) and antennae. Flavonoids identified from host plant extracts are known to stimulate oviposition. Scanning electron microscopy revealed the presence of contact-chemoreceptor sensilla on all appendages that contact the leaf surface. This electrophysiological study was conducted to identify the contact chemoreceptors that are sensitive to the known oviposition stimuli and are therefore probably involved in host recognition. Receptor cells of conspicuous sensilla grouped in clusters on fore-tarsi of females were sensitive to the behaviourally active butanol fraction of host plant (Asclepias curassavica) extract. However, these receptors generally had low sensitivity to three oviposition-stimulating flavonoids identified from this fraction, but they were also sensitive to the butanol fraction of a non-host (Brassica oleracea). Chemoreceptors in sensilla of the tarsomers 2–4 of the mid-legs also responded to the behaviourally active fraction of host plant extract and showed some sensitivity to two of the flavonoids that stimulate oviposition. Similar results were obtained from receptor cells in sensilla on the tip of the antennae. Most of these sensilla had cells responding to the butanol fraction of A. curassavica extract but only 25% of them were also sensitive to one of the behaviourally active flavonoids. These electrophysiological results, in combination with behavioural observations, suggest that host selection in monarch butterflies relies on a complex pattern of peripheral sensory information from several types of tarsal and antennal contact chemoreceptors.     

Effects of eucalypt nutritional quality on the Bog gum‐Victorian metapopulation of Ctenarytaina bipartita and implications for host and range expansion

1. Novel hosts present phytophagous insects with nutritional challenges which can cause host‐associated divergence. 2. The performance of the Bog gum‐Victorian metapopulation of Ctenarytaina bipartita Burckhardt et al. (Psylloidea:Aphalaridae), a psyllid whose range is being expanded by tree planting, on five species and genotypes of Eucalyptus endemic to south‐eastern Australia was quantified. Settling of females on two non‐hosts was also tested. 3. Female C. bipartita exhibited significant host‐associated plasticity in proctiger length (the body part used for oviposition into apical buds). Psyllids with longer wings and proctigers arose from a primary host. Fecundity varied significantly among hosts and was highest on a novel host. Hosts did not differ significantly in free amino acids (FAAs) but did differ in concentrations of essential amino acids (EAAs). However, nymphs did not differ significantly in EAAs. Surprisingly, fecundity was not related to total FAAs, availability of EAAs or concentrations of EAAs but was related to concentrations of four non‐EAAs. Mean fecundity per host was also positively related to the relative abundance of galloyl groups (associated with hydrolysable tannins). 4. Leaf age was more important to settling than eucalypt species; females settled on young leaves but this response was not related to leaf water content. 5. Planting the rare Eucalyptus kitsoniana in new habitats will expand the range of Bog gum‐Victorian C. bipartita and provide a bridge for the colonisation of novel eucalypts with buds suitable for oviposition. Host expansion by this metapopulation is not constrained by nutritional quality and may result in morphological divergence.     

Phenotypic plasticity in host plant preference of the willow leaf beetle Phratora vulgatissima: the impact of experience made by adults

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Flexible patch time allocation by the leafminer parasitoid, Opius dimidiatus

Abstract.

• 1 The ability to use flexible decision rules can be an advantage to parasitoid females searching for patchily-distributed hosts. In a series of laboratory experiments the hypothesis that Opius dimidiatus, a solitary parasitoid of the chrysanthemum leafminer (Liriomyza trifolii), adjusts the time she allocates to searching for her larval hosts in response to both patch qualities and experiences with hosts was tested by varying such patch parameters as area, presence of host mines and density of host mines, and by allowing ovipositions and encounters with parasitized hosts.
• 2 Though leaf area was not a factor, the presence of host mines in a leaf did increase the time a female O.dimidiatus spent searching, over time spent on unmined leaves.
• 3 When host mine density was increased, females responded by increasing their search period in a density-dependent manner, suggesting a perception of patch quality.
• 4 Ovipositions in hosts caused females to reset their‘giving-up time’(GUT), or increase search intensity, by adding an amount of search time that increased with each successive oviposition. Conversely, encounters with parasitized (unsuitable) hosts incremented the GUT, but by an amount that decreased with each successive encounter.

     

Larval food affects oviposition preference,female fecundity and offspring survival in Yponomeuta evonymellus

1. Yponomeuta evonymellus is a monophagous moth that feeds on Prunus padus which is native to Europe. In recent years, larval feeding and egg clusters have also been observed on non‐native Prunus serotina plants; however, survival of larvae on this new host is very low. 2. The objective of the present study was to determine how the feeding of larvae on each of the two host plants impacts oviposition, offspring survival and fecundity in Y. evonymellus. Our hypothesis was that, under controlled conditions, females will lay eggs on the host on which they fed as larvae. We also hypothesised that the lower survival of young larvae feeding on P. serotina was due to the smaller buds and leaves present in this species, relative to those of P. padus. 3. A dual‐choice experiment conducted under laboratory conditions demonstrated that females preferentially chose to oviposit on the plant species on which they fed as larvae. In the experiment, potential fecundity and offspring survival were significantly higher on P. padus than on P. serotina. The reduced performance of Y. evonymellus on P. serotina was correlated with a smaller bud mass and volume, lower leaf mass and surface area, and difficulty in constructing a protective tent against unfavourable weather conditions. 4. In summary, the identity of the host plant species during larval feeding determines adult oviposition preference for that host species. The survival of larvae on P. serotina growing in the nature is low, but for phenology‐related reasons.     

Experience-induced preference for oviposition repellents derived from a non-host plant by a specialist herbivore

Foraging adults of phytophagous insects are attracted by host‐plant volatiles and supposedly repelled by volatiles from non‐host plants. In behavioural control of pest insects, chemicals derived from non‐host plants applied to crops are expected to repel searching adults and thereby reduce egg laying. How experience by searching adults of non‐host volatiles affects their subsequent searching and oviposition behaviour has been rarely tested. In laboratory experiments, we examined the effect of experience of a non‐host‐plant extract on the oviposition behaviour of the diamondback moth (DBM), Plutella xylostella, a specialist herbivore of cruciferous plants. Naive ovipositing DBM females were repelled by an extract of dried leaves of Chrysanthemum morifolium, a non‐host plant of DBM, but experienced females were not repelled. Instead they were attracted by host plants treated with the non‐host‐plant extract and laid a higher proportion of eggs on treated than on untreated host plants. Such behavioural changes induced by experience could lead to host‐plant range expansion in phytophagous insects and play an important role in determining outcome for pest management of some behavioural manipulation methods.     

Host selection,oviposition behaviour and leaf traits in a specialist willow sawfly on species of Salix (Salicaceae)

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