Host utilisation by moth and larval survival of pine processionary caterpillar Thaumetopoea pityocampa in relation to food quality in three Pinus species

Abstract 1. The work reported here analysed host utilisation by the pine processionary moth Thaumetopoea pityocampa (Lepidoptera: Thaumetopoeidae), the relationship between moth oviposition patterns and larval performance, the chemical characteristics of the plant in relation to the performance of different larval instars, and the role of these factors in the outbreak capacity of the species. In order to do this, a combination of field and laboratory techniques was used to study three pine species differing in nutritional characteristics.
2. Moths oviposited in the three pine species analysed, although cluster pine received a lower number of batches. Late-instar larvae were able to feed on all three pine species, however first-instar larvae developed on Scots and black pine but died on cluster pine. Consequently, oviposition in cluster pine can be considered an oviposition mistake, and indicates that moths are rather unselective when ovipositing on different pine species.
3. Chemical analysis of needles suggested that the quantity of nitrogen was the main factor responsible for the difference in survival of larvae.
4. The oviposition pattern of the moth and the larval susceptibility to food quality in Thaumetopoea pityocampa agree with the theory that unselective oviposition of the moth is a precondition for eruptive dynamics in phytophagous insects.
5. The success of the larvae depends mainly on the probability of the moth finding a suitable host. This probability is determined strongly by the changes of structure and coverage in Mediterranean pine woodlands, due to human management.     

The relationships between host selection and subsequent larval performance in three free-living graminivorous sawflies

1. Selection of host plants for oviposition by females of three graminivorous sawfly species, Dolerus puncticollis C. G. Thomson, Dolerus picipes Klug. and Pachynematus clitellatus Lepeletier, was investigated experimentally using three grass species, Lolium perenne L., Festuca rubra L. and wheat, Triticum aestivum L. cv. Hunter.
2. Both species of Dolerus showed significant preferences for one grass over the other two, D. puncticollis preferring L. perenne and D. picipes selecting F. rubra. P. clitellatus females used L. perenne and F. rubra equally for oviposition, but avoided wheat.
3. The results correlated closely with larval performance trials, with D. puncticollis larvae having maximal survival and growth rates on L. perenne , and D. picipes larval performance being maximized on F. rubra. P. clitellatus larvae survived well on both grasses, but had a high level of mortality on wheat.
4. P. clitellatus larval growth rates were significantly higher on L. perenne than on F . rubra . Individual P. clitellatus adult females developing from larvae reared on L. perenne reached a significantly greater dry weight than those reared on F. rubra , but there was no significant difference in weight between males reared on the two hosts. There was some evidence that this disproportionate effect of host plant quality on the weight gain of the two sexes was translated into a bias in sex ratio of the eggs laid towards a greater proportion of females on L. perenne than on F. rubra . This manipulation of sex ratio would have a potential benefit for ovipositing females through disproportionate fecundity gains for female offspring.     

Desiccation of Pinus foliage induced by conifer sawfly oviposition: effect on egg viability

Abstract 1. Desiccation of needles following oviposition by Neodiprion lecontei in Pinus resinosa caused high egg mortality. Eight-five per cent of pine needles into which sawflies oviposited subsequently desiccated, compared with 2.5% of needles without eggs. No larval emergence occurred from desiccated needles.
2. Within affected shoots, the probability of desiccation increased with the extent of oviposition. In paired comparisons of needles, 41.2% of needle length was occupied by eggs in desiccated needles, compared with 24.0% of needles without desiccation.
3. Both density-dependent and density-independent factors may contribute to desiccation of egg-laden needles. The likelihood that needle vasculature will be severed by ovipositing females probably increases with population density. Drought, which was high during the observations, probably increases the incidence of needle desiccation following mechanical injury caused by oviposition.     

Assessment of patch quality by ladybirds: role of larval tracks

Gravid females of the two-spot ladybird, Adalia bipunctata (L.), were deterred from ovipositing when kept in petri dishes that had previously contained conspecific larvae but not conspecific adults, or the larvae of another two species of ladybird, Adalia decempunctata (L.) and Coccinella septempunctata L. The deterrent effect was density dependent and mediated via a chloroform-soluble contact pheromone present in the larval tracks. Similarly, gravid females of C. septempunctata were deterred from ovipositing by conspecific larval tracks and chloroform extracts of these tracks, but not by the tracks or extracts of tracks of A. bipunctata larvae. That is, in ladybirds the larvae produce a species-specific oviposition-deterring pheromone. In the field, the incidence of egg cannibalism in ladybirds increases very rapidly with the density of conspecific eggs or larvae per unit area. Thus, in responding to the species specific oviposition deterring pheromone female ladybirds reduce the risk of their eggs being eaten and spread their offspring more equally between patches. Received: 14 March 1997 / Accepted: 26 August 1997     

Diamondback moth females oviposit more on plants infested by non‐parasitised than by parasitised conspecifics

Abstract 1. When offered a choice, female diamondback moths (Plutella xylostella) oviposited more eggs on plants with non‐parasitised conspecific larvae than on plants with parasitised larvae. 2. The leaf area consumed by parasitised larvae was significantly lower than that by non‐parasitised larvae. However, this quantitative difference in larval damage did not explain the female’s ability to discriminate between plants with parasitised and non‐parasitised larvae, as females showed an equal oviposition preference for plants infested by higher or lower densities of non‐parasitised larvae. 3. Pupal weight and duration of the larval stage of P. xylostella were independent of whether larvae were reared on plants that were previously infested by either non‐parasitised or parasitised larvae. 4. The larval parasitoid Cotesia vestalis did not distinguish between plants infested by non‐parasitised larvae and plants infested by larvae that had already been parasitised by conspecific wasps. 5. Based on these data, it can be concluded that the moth oviposition preference for plants infested by non‐parasitised conspecifics relative to plants infested by parasitised conspecifics was not explained by plant quality or by the attractiveness of plants towards wasps. It is hypothesised that one of the reasons for this preference is avoidance of plants where a relatively high risk of parasitism is expected due to the emergence of parasitoids from the parasitised host larvae.     

Gene-for-gene defense of wheat against the Hessian fly lacks a classical oxidative burst

Genetic similarities between plant interactions with microbial pathogens and wheat interactions with Hessian fly larvae prompted us to investigate defense and counterdefense mechanisms. Plant oxidative burst, a rapid increase in the levels of active oxygen species (AOS) within the initial 24 h of an interaction with pathogens, commonly is associated with defenses that are triggered by gene-for-gene recognition events similar to those involving wheat and Hessian fly larvae. RNAs encoded by Hessian fly superoxide dismutase (SOD) and catalase (CAT) genes, involved in detoxification of AOS, increased in first-instar larvae during both compatible and incompatible interactions. However, mRNA levels of a wheat NADPH oxidase (NOX) gene that generates superoxide (O2-) did not increase. In addition, inhibiting wheat NOX enzyme with diphenyleneiodonium did not result in increased survival of avirulent larvae. However, nitro blue tetrazolium staining indicated that basal levels of O2- are present in both uninfested and infested wheat tissue. mRNA encoded by wheat genes involved in detoxification of the cellular environment, SOD, CAT, and glutathione-S-transferase did not increase in abundance. Histochemical staining with 3,3-diaminobenzidine revealed no increases in wheat hydrogen peroxide (H2O2) during infestation that were correlated with the changes in larval SOD and CAT mRNA. However, treatment with 2',7'-dichlorofluorescin demonstrated the presence of basal levels of H2O2 in the elongation zone of both infested and uninfested plants. The accumulation of a wheat flavanone 3-hydroxylase mRNA did show some parallels with larval gene mRNA profiles. These results suggested that larvae encounter stresses imposed by mechanisms other than an oxidative burst in wheat seedlings.     

Obviation of wheat resistance to the Hessian fly through systemic induced susceptibility

Unlike most documented plant-insect interactions, Hessian fly-resistance [Mayetiola destructor (Say)] in wheat (Triticum aestivum L.) is initiated by a gene-for-gene recognition event in which plants carrying a specific R gene recognize salivary effectors encoded by a corresponding larval avirulence gene. However, dual infestation resulting from oviposition by virulent insects from 5 d before to 3 d after oviposition by avirulent insects on the same host plant, lead to systemic induced susceptibility, obviation of resistance, and ultimately the survival of both virulent and genetically avirulent progeny to adulthood. Simultaneous oviposition allowed greater survival of avirulent progeny than ovipositions separated by larger intervals. Because of the induction of plant resistance, hatch of avirulent larvae before virulent was more detrimental to rate of development than hatch of virulent before avirulent larvae. Obviation of resistance was not localized to the leaf being attacked by the virulent larvae, but also functioned across spatial distance into younger leaves. This research suggests that virulent Hessian fly larvae directly suppress the defense response of wheat, thus providing a refuge for avirulent genotypes, preserving diversity in field populations and increasing durability of deployed resistance genes.     

Preference for plants damaged by conspecific larvae in ovipositing cabbage root flies: influence of stimuli from leaf surface and roots

In laboratory dual-choice assays females of the cabbage root fly, Delia radicum, prefer for oviposition plants with roots damaged by conspecific larvae to undamaged controls. Cauliflower and kale plants were inoculated with root fly eggs (25 per plant) and the hatching larvae were allowed to feed on the roots for various periods of time (1–17 days). After 4 (cauliflower) or 5 (kale) days of larval feeding the oviposition preference was most pronounced and flies laid between 64% and 68% of their eggs near plants with damaged roots. Later, with increasing damage but fewer surviving, and thus actively feeding, larvae, the magnitude of the preference declined. The preference for plants already damaged by conspecific larvae may contribute to the previously observed aggregated distribution of D. radicum eggs in Brassica crop fields.Further experiments revealed that the sensory cues inducing this oviposition preference originate from the complex consisting of the damaged roots, the surrounding substrate (soil) and associated microbes, rather than from the aerial plant parts. In choice assays using the root-substrate complex of damaged and control plants (aerial parts removed), the observed preference for damaged roots was similar to that found for the entire plant but was more pronounced. The damaged roots alone, compared to control roots, received up to 72% (cauliflower) and 75% (kale) of the eggs. By contrast, surrogate leaves sprayed with methanolic leaf surface extracts from the most preferred plants which had been damaged were not discriminated from surrogate leaved sprayed with extracts of the respective control plants. Analysis of glucosinolate levels in methanolic leaf surface extracts revealed that root damage resulted in enhanced concentrations of indole-glucosinolates on the leaf surface in kale but not in cauliflower. Although indole-glucosinolates are oviposition stimulants for the cabbage root fly, the induced changes were apparently too small to influence oviposition behaviour.     

Oviposition decreased in response to enriched water: a field study of the pitcher-plant mosquito, Wyeomyia smithii

Abstract.  1. Environmental cues are known to influence oviposition behaviour in mosquitoes, with important consequences for larval survival and insect population dynamics. Enriched microhabitats have been shown to be preferred oviposition sites.
2. In a field experiment designed to determine whether ovipositing mosquitoes are sensitive to different levels of nutrient enrichment, new pitcher-plant ( Sarracenia purpurea ) leaves were opened and enriched with 0, 2, or 20 dead ants, and the number of pitcher-plant mosquito ( Wyeomyia smithii ) larvae resulting from subsequent oviposition were measured.
3. Oviposition rates were higher in leaves with low levels of enrichment (0 and 2 ants per leaf), although larval development was enhanced at the highest enrichment level.
4. Results suggest that, although these mosquito larvae are nutrient limited, ovipositing females preferentially avoid highly enriched leaves. This counterintuitive result may be due to low oxygen concentrations or a masked cue in enriched leaves, and contrasts with other oviposition studies.     

Oviposition patterns of the pine weevil Hylobius abietis

Spatial and temporal distributions of eggs laid by the pine weevil Hylobius abietis (L.) (Coleoptera: Curculionidae) were studied by taking root and soil samples around pine stumps on a clear-cutting in central Sweden. In addition, first-instar larvae migrating in the soil were sampled using traps baited with host-odour. Eggs were found in the soil rather than in the bark of stump roots, which previously has been regarded as the usual oviposition site. Based on an oviposition experiment and additional field observations we conclude that eggs are laid in the bark of roots only when the surrounding material is likely to dry out. We suggest two explanations for why weevils oviposit mainly in the soil, although they are known to show stereotypic behaviour when inserting eggs in stump roots: (1) egg predation by other arthropods or by conspecifics is avoided, and (2) newly hatched pine weevil larvae are better than ovipositing females at locating suitable sites for larval feeding.     

Leaf ties as colonization sites for forest arthropods: an experimental study

Abstract.  1. Secondary colonization of leaf shelters constructed by caterpillars has been reported from a number of systems. Both the mechanism (larval or adult movement vs. oviposition) and the cues used by arthropods in locating leaf shelters, however, have received little attention.
2. Artificial leaf shelters (i.e. leaf ties or pairs of leaves clipped together to form sandwiches) were constructed on understorey white oak ( Quercus alba L.) trees and the abundance and species composition of arthropods colonizing and ovipositing on leaf pairs was examined in three treatments: occupied leaf ties (containing a leaf-tying caterpillar), unoccupied leaf ties, and non-tied control leaves.
3. The density of arthropods present in the occupied and unoccupied leaf ties after two weeks was seven and four times greater respectively, than non-tied controls. The guild composition of these early colonists differed among treatments, with the highest densities of leaf chewers, scavengers, and predators in occupied ties and the lowest densities in non-tied controls.
4. The densities of all arthropods ovipositing on leaf pairs in the occupied and unoccupied leaf tie treatments were four and three times greater than non-tied controls. Leaf-chewing insects (including leaf-tiers and non-tying inquiline species) and scavengers showed strong oviposition preferences for tied leaves. However, most species of leaf-tying caterpillars and the psocids (Psocoptera) did not distinguish between occupied and unoccupied ties, suggesting that these groups do not use occupancy-related cues in selecting oviposition sites.     

Particle films for suppression of the codling moth (Lepidoptera: Tortricidae) in apple and pear orchards

Studies were conducted in 1997 and 1998 to evaluate the effects of three particle film formulations consisting of kaolin and adjuvants on neonate larvae, ovipositing adult females, and eggs of the codling moth, Cydia pomonella (L.). Neonate larval walking speed, fruit discovery rate, and fruit penetration rate on apple host plants coated with particle films were significantly lower than on host plants without particle films in laboratory assays. Females oviposited less on host plants covered with a particle film residue than on untreated plants in laboratory choice and no-choice tests. Hatch rate of codling moth neonate larvae was unaffected by particle films sprayed on host plants either before or after oviposition. Fruit infestation rates were significantly reduced on particle film-treated trees compared with untreated trees for both first- and second-generation codling moth in field trials in both apple and pear orchards. Particle films appear to be a promising supplemental control approach for codling moth in orchards where moth density is high, and may represent a stand-alone method where moth densities are lower.     

The influence of host plant variation and intraspecific competition on oviposition preference and offspring performance in the host races of Eurosta solidaginis

1. A series of experiments was conducted to measure the impact of plant genotype, plant growth rate, and intraspecific competition on the oviposition preference and offspring performance of the host races of Eurosta solidaginis (Diptera: Tephritidae), a fly that forms galls on Solidago altissima and Solidago gigantea (Asteraceae). Previous research has shown that both host races prefer to oviposit on their own host plant where survival is much higher than on the alternate host plant. In this study, neither host race showed any relationship between oviposition preference and offspring performance in choosing among plants of their natal host species. 2. The larval survival of both host races differed among plant genotypes when each host race oviposited on its natal host species. In one experiment, altissima host race females showed a preference among plant genotypes that was not correlated with offspring performance on those genotypes. In all other experiments, neither the altissima nor gigantea host race demonstrated a preference for specific host plant genotypes. 3. Eurosta solidaginis had a preference for ovipositing on rapidly growing ramets in all experiments, however larval survival was not correlated with ramet growth rate at the time of oviposition. 4. Eurosta solidaginis suffered high mortality from intraspecific competition in the early larval stage. There was little evidence, however, that females avoided ovipositing on ramets that had been attacked previously. This led to an aggregated distribution of eggs among ramets and strong intraspecific competition. 5. There was no interaction among plant genotype, plant growth rate, or intraspecific competition in determining oviposition preference or offspring performance.     

Oviposition preference of Lygocoris pabulinus (Het., Miridae) in relation to plants and conspecifics

Abstract: To predict possible locations of Lygocoris pabulinus (L) in the field during the summer, we determined their oviposition preference under summer conditions. With L. pabulinus reared on potato, oviposition preference was determined for potato, tomato or green bean. As preference may depend on larval or early adult experience, the oviposition preference of bugs reared on green bean for three generations, and of bugs captured from the field 12 h prior to the experiment was also determined. All females showed a strong preference for potato plants, on which fecundity was higher. Hence, although L. pabulinus is a generalist in its feeding habits, the summer generation seems to be an oviposition specialist. Aggregation of ovipositing females does not seem to occur; similar amounts of eggs were oviposited in plants with clip cages containing conspecifics as in plants without conspecifics. More eggs were oviposited in damaged plants than in undamaged plants. Plant volatiles released upon damage may aid L. pabulinus females in finding suitable oviposition sites.     

Oviposition preference and larval performance and behavior of <Emphasis Type="Italic">Trichoplusia ni</Emphasis> (Lepidoptera: Noctuidae) on host and nonhost plants

We investigated the female oviposition preference and larval performance and behavior of Trichoplusia ni (Hubner) on cabbage, tomato, soybean (host plants), and wormseed (nonhost plant) in laboratory experiments. In addition, we investigated the role of trichomes in the oviposition of females. Females oviposited more often on cabbage than on tomato, soybean, or wormseed plants. Tomato was the second most preferred plant, followed by soybean and wormseed. Neonate larvae gained more weight on cabbage and tomato than on soybean or wormseed, while second-instar larvae grew better on cabbage than on tomato, soybean, or wormseed. The least growth of neonate larvae occurred on wormseed plants. The orientation of neonate and second-instar larvae to cabbage, tomato, soybean, and wormseed did not differ significantly. Neonate larvae settled equally on leaf discs of cabbage, tomato, soybean, and wormseed, while most second-instar larvae settled on leaf discs of cabbage in comparison with the other plants after 24 h of release. The foliar area consumed by neonate larvae was quite similar among plants, but second-instar larvae consumed more cabbage than tomato, soybean, or wormseed. Comparing different types of leaves, females oviposited more often on mature than young leaves of tomato, soybean, and wormseed. In contrast, females did not show any preference for ovipositing on young or mature leaves of cabbage. In general, we found that the density or length of nonglandular and glandular trichomes of tomato, soybean, and wormseed plants negatively affected oviposition of T. ni females.     

Behavioral cues associated with oviposition by Trioza eugeniae

Trioza eugeniae oviposited significantly more eggs on Syzygium paniculatum leaves free of eggs compared to leaves with pre-existing eggs in a choice experiment, suggesting that females modify oviposition based on cues associated with the presence of eggs. In separate experiments, females avoided ovipositing on parts of leaves where eggs were present, but readily oviposited on areas of the same leaf without eggs. Epideictic pheromones are apparently not used by this species because females readily oviposited on areas of a leaf from which eggs had previously been removed. Females laid 57% of all their eggs along the margins of normal leaves, but also oviposited on artificial margins produced by cutting the leaves. The preference for natural margins over artificial margins was eliminated when the entire margin was coated with an antitranspirant compound to mask the damaged edge. These studies show that ovipositing psyllids respond both to the presence of eggs and to the suitability of the substrate.     

Role of bacteria in the oviposition behaviour and larval development of stable flies

Stable flies, Stomoxys calcitrans (L.), are the most important pests of cattle in the United States. However, adequate management strategies for stable flies, especially for pastured cattle, are lacking. Microbial/symbiont-based approaches offer novel venues for management of insect pests and/or vector-borne human and animal pathogens. Unfortunately, the fundamental knowledge of stable fly-microbial associations and their effect on stable fly biology is lacking. In this study, stable flies laid greater numbers of eggs on a substrate with an active microbial community (> 95% of total eggs oviposited) than on a sterilized substrate. In addition, stable fly larvae could not develop in a sterilized natural or artificial substrate/medium. Bacteria were isolated and identified from a natural stable fly oviposition/developmental habitat and their individual effect on stable fly oviposition response and larval development was evaluated in laboratory bioassays. Of nine bacterial strains evaluated in the oviposition bioassays, Citrobacter freundii stimulated oviposition to the greatest extent. C. freundii also sustained stable fly development, but to a lesser degree than Serratia fanticola. Serratia marcescens and Aeromonas spp. neither stimulated oviposition nor supported stable fly development. These results demonstrate a stable fly bacterial symbiosis; stable fly larval development depends on a live microbial community in the natural habitat, and stable fly females are capable of selecting an oviposition site based on the microbially derived stimuli that indicate the suitability of the substrate for larval development. This study shows a promising starting point for exploiting stable fly-bacterial associations for development of novel approaches for stable fly management.     

Resource selection by female moths in a heterogeneous environment: what is a poor girl to do?

1. According to the preference-performance hypothesis, female insects select resources that maximize offspring performance. To achieve high fitness, leaf miner females should then adjust their oviposition behaviour in response to leaf attributes signalling high host quality. 2. Here we investigate resource selection in Tischeria ekebladella, a leaf-mining moth of the pedunculate oak (Quercus robur), in relation to two alternative hypotheses: (1) females select their resources with respect to their future quality for developing larvae; or (2) temporal changes in resource quality prevent females from selecting the best larval resources. 3. Specifically, we test whether females show the strongest selection at the levels at which quality varies the most (shoots and leaves); whether they respond to specific leaf attributes (leaf size, phenolic content and conspecific eggs); and whether female preference is reflected in offspring performance. 4. Female choice of leaves was found to be non-random. Within trees, the females preferred certain shoots, but when the shoots were on different trees the degree of discrimination was about four times larger than when they were on the same trees. 5. While females typically lay more eggs on large leaves, this is not a result of active selection of large leaves, but rather a result of females moving at random and ovipositing at regular intervals. 6. The females in our study did not adjust their oviposition behaviour in response to leaf phenolic contents (as measured by the time of larval feeding). Neither did they avoid leaves with conspecific eggs. 7. Female choice of oviposition sites did not match patterns of offspring performance: there was no positive association between offspring survival and counts of eggs. 8. We propose that temporal variation in resource quality may prevent female moths from evaluating resource quality reliably. To compensate for this, females may adopt a risk-spreading strategy when selecting their resources.     

The role of medium conditioning in the population dynamics of the housefly

The role of larval medium conditioning on the behavior of larvae and of ovipositing adults of the housefly, Musca domestica L., was investigated through behavioral preference tests. Larvae were strongly attracted to medium conditioned by themselves or other larvae, while adult females overwhelmingly oviposited in fresh medium. Medium conditioning occurs within a few hours after hatching of an egg cohort and is effective in preventing overcrowding of a single site by shutting off further oviposition within 24 hours after eggs are initially deposited. A model of medium conditioning optimizes density for developing larvae and could also provide for regulation of local larval populations.     

异色瓢虫不同龄期幼虫踪迹对受孕雌虫产卵的影响

本文通过室内试验研究了异色瓢虫Harmonia axyridis (Pallas)不同龄期幼虫踪迹对受孕雌虫在猎物寄主上停留时间和产卵的影响。结果表明:受孕雌虫倾向于在猎物丰富的植株上停留。幼虫踪迹抑制了受孕异色瓢虫雌虫的停留时间,但2龄幼虫踪迹和4龄幼虫踪迹对受孕雌虫停留时间的影响差异不显著。异色瓢虫雌虫将卵产于有蚜虫的植株上,幼虫踪迹对受孕雌虫的产卵抑制作用显著,但2龄和4龄幼虫踪迹的抑制效果差异不明显。