Models of the spatial pattern of egg population of Ranunculus leaf mining fly,Phytomyza ranunculi (Diptera: Agromyzidae), in host leaves

This paper considers two kinds of model of the spatial pattern of egg distribution of the Ranunculus leaf mining fly, Phytomyza ranunculiSchrank , as a step to determining the effect of the distribution upon the parasitism of this species by the eulophid parasite, Kratochviliana sp.. Each model incorporates submodels in several important stages of both the processes of visiting and subsequent oviposition by the fly. Model 2 is more general than model 1, because the former also includes the effect of oviposition restraint. Both models fitted well the egg distribution on fresh plants and on exploited plants. The fitting similarity on exploited plants is due to the fact that there were not so many heavily exploited leaves which lead to oviposition restraint, owing to the low density of mature larvae contained in the leaves. These models will be applicable to the distribution of larvae as well as eggs, because most larvae remain in the leaf where they occurred as eggs, until emerging just before pupation. This paper also discusses by use of these models the fact that this fly tends to effectively avoid excessive oviposition in leaves by laying fewer eggs per visit and visiting leaves more sparsely and also by refraining from further oviposition on leaves exploited heavily by mature larvae.     

The importance of non-linearity: A comment on the views of Taylor

Taylor's (1984) view that his power law is better measurement of the distribution pattern of animals than 1/k, I_ρ and relation because almost all the data on means and variances of given species could be fitted by the power low, was critisized. Changes in values of 1/k, I_ρ and suggest the change of distribution pattern of the species, but the data can still be fitted by the power law because of the great linearizing power of log-log plots, and, using the power law only, we shall overlook the information on the meaningful changes in the distribution pattern.     

Studies on the interspecies competition between the azuki bean weevil and the southern cowpea weevil IV. Competition between strains

This study analyzes results of interspecies competition between the azuki bean weevil, Callosobruchus chinensis and the southern cowpea weevil, C. maculatus using the four geographical strains of each species.

1. Fifteen combinations of one strain from each species were set up to compete. The strains of C. chinensis, rather than of C. maculatus, characteristically determine the eventual outcomes of competition. Some strains of C. chinensis (jC and kC) invariably won every encounter with C. maculatus. Another strain (nC) always lost its encounters, while one other strain (iC) won some encounters (:cQ and :cQ) and lost others (:tQ and :bQ). For any combination the competition results were deterministic and no reversal in outcome was observed among the replicates.
2. The weakness of strain nC in competition is explained by its characteristics in single species populations, different greatly from other strains of C. chinensis, although it had the similar primary (individual) characteristics as other strains of C. chinensis. Strain iC had the shortest adult longevity in the four strains of C. chinensis although it behaved similar to strain jC at the single species population level. Especially under the food supply schedule of the present experiment the shortness of adult longevity might be the important factor determining the outcome.
3. The relationship of the eight strains based on the individual and single species population characteristics, and that based on the competition results were very similar. Even when the competition results could not be explained by any one or two of these characteristics alone, the outcome would be largely decided by the overall biotic profile made by several characteristics.

     

Sibling and non-sibling cannibalism by larvae of a lady beetleHarmonia axyridis Pallas (Coleoptera: Coccinellidae) in the field

Sibling (cannibalism among siblings) and non-sibling cannibalism (cannibalism among non-siblings) were studied in a natural population of a lady beetle, Harmonia axyridisPallas . Of all the eggs laid (n=2269), 24.76% (n=562) were killed by sibling cannibalism and 36.10% (n=819) were killed by non-sibling cannibalism. Sibling cannibalism occurred constantly and intensively in most egg batches throughout the entire oviposition period. On the other hand, non-sibling cannibalism was more intense in the middle and late oviposition periods, and when the egg batches were close to an aphid colony. This may be due to the high density of H. axyridis larvae relative to aphid density in the middle and late oviposition periods and also the larvae searching intensively near an aphid colony.     

Dispersal as a means of inbreeding avoidance in a wild bird population

The long-term study of animal populations facilitates detailed analysis of processes otherwise difficult to measure, and whose significance may appear only when a large sample size from many years is available for analysis. For example, inbreeding is a rare event in most natural populations, and therefore many years of data are needed to estimate its effect on fitness. A key behaviour hypothesized to play an important role in avoiding inbreeding is natal dispersal. However, the functional significance of natal dispersal with respect to inbreeding has been much debated but subject to very few empirical tests. We analysed 44 years of data from a wild great tit Parus major population involving over 5000 natal dispersal events within Wytham Woods, UK. Individuals breeding with a relative dispersed over several-fold shorter distances than those outbreeding; within the class of inbreeding birds, increased inbreeding was associated with reduced dispersal distance, for both males and females. This led to a 3.4-fold increase (2.3-5, 95% CI) in the likelihood of close (f=0.25) inbreeding relative to the population average when individuals dispersed less than 200m. In the light of our results, and published evidence showing little support for active inbreeding avoidance in vertebrates, we suggest that dispersal should be considered as a mechanism of prime importance for inbreeding avoidance in wild populations.     

Attack behavior and host size selection by Diglyphus begini on Liriomyza trifolii in chrysanthemum

Diglyphus begini (Ashmead) (Hymenoptera: Eulophidae) is a larval ectoparasitoid of the leafminer, Liriomyza trifolii (Burgess) (Diptera: Agromyzidae). Female wasps oviposit on larvae which are significantly larger than larvae utilized for host feeding or hosts rejected for oviposition or feeding. Host size is evaluated on a relative rather than absolute basis. Individual female reproductive success increases with host size because of accompanying increases in offspring survivorship and adult body size. The number and duration of parasitoid stings is significantly greater when host feeding compared to oviposition and host rejection due to extensive probing of the internal viscera of larvae with the female ovipositor when host feeding. Upon host paralysis, 47.5% of parasitoid eggs become displaced from their host. However, eggs experimentally placed a mean distance of 0.8 mm away from a host do not result in a reduction in offspring survivorship compared to eggs attached to a host.

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Résumé La mineuse L. trifolii Burgess attaque de nombreuses cultures à travers le monde. L'eulophide, D. begini Ashmead, est un parasitoïde fréquent du diptère. L'objectif de nombreux praticiens de la lutte biologique est de pouvoir prédire le résultat de lâchers d'ennemis naturels. Cette étude a été entreprise en estimant que la connaissance du comportement de prospection aide á comprendre la dynamique des interactions des populations hôtes et parasites. Une attaque de D. begini se concrétisant par une ponte, est généralement caractérisée par deux piqûres de durée limitée avec émission de l'uf normalement au cours de la seconde piqûre.L'alimentation aux dépens de l'hôte est caractérisée par des piqûres prolongées et répétées. Les hôtes refusés pour la ponte ou l'alimentation sont piqués une fois ou deux, les deux piqûres étant très brèves.L'aptitude de D. begini à percevoir les différences de tailles des larves de L. trifolii augmente la valeur adaptative individuelle des parasites. Les femelles ne pondent que dans les hôtes les plus grands, ce qui augmente le taux de survie des descendants et la taille des adultes. Puisque la taille des hôtes est évaluée sur une base relative, la valeur adaptative du parasite est indépendante des changements de distribution des tailles des hôtes rencontrés. Les larves de L. trifolii utilisées comme hôtes ne deviennent pas immédiatement immobiles après avoir été attaquées. Ceci fait que de nombreux ufs peuvent être délogés de leur hôte. Nous avons été incapables de déceler quelque effet nocif de ces mouvements de l'hôte après la ponte sur la survie des ufs de D. begini.

     

Influence of aphid size,age and behaviour on host choice by the parasitoid wasp Ephedrus californicus: a test of host-size models

Summary When host quality varies, parasitoid wasps are expected to oviposit selectively in high-quality hosts. We tested the assumption underlying host-size models that, for solitary species of wasps, quality is based on host size. Using Ephedrus californicus, a solitary endoparasitoid of the pea aphid, we evaluated the influence of aphid size (= mass), age and defensive behaviours on host selection. Experienced parasitoid females were given a choice among three classes of 5-day-old apterous nymphs: small aphids that had been starved daily for 4 h (S4) and 6 h (S6) respectively, and large aphids permitted to feed (F) normally. Wasps attacked more, and laid more eggs in, small than large aphids (S6>S4>F). This rank-order for attack did not change when females could choose among aphids of the same size that differed in age; however, wasps oviposited in all attacked aphids with equal probability. Host size did not influence parasitoid attack rates when aphids were anaesthetized so that they could not escape or defend themselves. As predicted by host-size models, wasp size increased with host size (F>S4; S6), but large wasps required longer to complete development than their smaller counterparts (S4E. californicus reflects a trade-off between maximization of fitness gains per egg and the economics of search-time allocation. Because large aphids are more likely to escape parasitization, a wasp must balance her potential gain in fitness by ovipositinng in a high-quality (large) aphid against her potential cost in terms of lost opportunity time if the attack fails.     

Fine-scale population structure, inbreeding risk and avoidance in a wild insect population

The ecological and evolutionary importance of fine-scale genetic structure within populations is increasingly appreciated. However, available data are largely restricted to wild vertebrates and eusocial insects. In addition, there is the expectation that most insects tend to have such large- and high-density populations and are so mobile that they are unlikely to face inbreeding risks through fine-scale population structuring. This has made the growing body of evidence for inbreeding avoidance in insects and its implication in mating systems evolution somewhat enigmatic. We present a 4-year study of a natural population of field crickets. Using detailed video monitoring combined with genotyping, we track the movement of all adults within the population and investigate genetic structure at a fine scale. We find some evidence for relatives being found in closer proximity, both across generations and within a single breeding season. Whilst incestuous matings are not avoided, population inbreeding is low, suggesting that mating is close to random and the limited fine-scale structure does not create significant inbreeding risk. Hence, there is little evidence for selective pressures associated with the evolution of inbreeding avoidance mechanisms in a closely related species.     

The role of female search behaviour in determining host plant range in plant feeding insects: a test of the information processing hypothesis

Recent theoretical studies have suggested that host range in herbivorous insects may be more restricted by constraints on information processing on the ovipositing females than by trade-offs in larval feeding efficiency. We have investigated if females from polyphagous species have to pay for their ability to localize and evaluate plants from different species with a lower ability to discriminate between conspecific host plants with differences in quality. Females of the monophagous butterflies Polygonia satyrus, Vanessa indica and Inachis io and the polyphagous P. c-album and Cynthia cardui (all in Lepidoptera, Nymphalidae) were given a simultaneous choice of stinging nettles (Urtica dioica) of different quality. In addition, the same choice trial was given to females from two populations of P. c-album with different degrees of specificity. As predicted from the information processing hypothesis, all specialists discriminated significantly against the bad quality nettle, whereas the generalists laid an equal amount of eggs on both types of nettle. There were no corresponding differences between specialist and generalist larvae in their ability to utilize poor quality leaves. Our study therefore suggests that female host-searching behaviour plays an important role in determining host plant range.     

Escaping an evolutionary trap: preference and performance of a native insect on an exotic invasive host

Exotic plants may act as population sinks or evolutionary traps for native herbivores. The native butterfly Pieris oleracea lays eggs on garlic mustard, Alliaria petiolata, but larvae develop very poorly on this exotic invasive plant. We examined oviposition preference of individual females and larval performance of their offspring for individuals from one area where garlic mustard is well established and one where it is absent. These data were used to assess whether garlic mustard is being incorporated into or excluded from the diet. Females from the area without garlic mustard showed a wide range of preference, families had low larval survival on garlic mustard, and larval survivorship showed no correlation with mothers’ preferences. Females from the area with garlic mustard preferred it to the native host, and larval survivorship on garlic mustard was positively correlated with the mother’s preference. Individuals surviving on garlic mustard took longer to pupate and weighed >30% less compared to pupae reared on normal hosts. Our results suggest that where garlic mustard is well established P. oleracea may be adapting to this plant by both improved larval performance and increased adult female oviposition preference for it.     

Costs of mating and egg production in female Callosobruchus chinensis

Costs of reproduction include the costs of mating and egg production. Specific techniques such as irradiation or genetic mutation have been used to divide the expense into costs of mating and egg production in previous studies. We tried to divide the costs in the adzuki bean beetle, Callosobruchus chinensis (Coleoptera: Bruchidae), which needs some kinds of bean as an oviposition substrate. Mated females that were not allowed to lay eggs had a shorter life span than virgin females, but they had a longer life span than mated females that were allowed to lay eggs. The results showed two independent significant costs, mating and egg production, on the life span in C. chinensis. Costs of mating, however, include the costs of sexual harassment by males and copulation itself, and we need further studies to divide the costs. The present method for dividing the cost of reproduction into costs of mating and egg production can be applied to a broad taxonomic range of insect species, and thus it will be a useful model system for inter-specific comparisons of costs of mating and egg production.     

Identification of amine receptors from a swallowtail butterfly, Papilio xuthus L.: cloning and mRNA localization in foreleg chemosensory organ for recognition of host plants

The swallowtail butterfly, Papilio xuthus L., feeds exclusively on members of the plant family, Rutaceae. Female butterflies lay eggs in response to specific chemicals contained in their host plants. They perceive a variety of polar compounds as oviposition stimulants through the tarsal chemosensilla of the foreleg by drumming upon the leaf surface. Some biogenic amine analogs have been characterized as oviposition stimulants. We have cloned three amine receptors, serotonin, tyramine, and dopamine, from cDNA derived from foreleg tarsus of P. xuthus, and determined structures of both cDNA and genomic genes. The phenylethylamine (tyramine and dopamine) receptors were expressed preferentially in brain and chemosensory organs. Moreover, we observed the localized expression of dopamine receptors at the base of tarsal chemosensilla by in situ hybridization. These results suggest that amine receptors in tarsal chemosensilla have a functional role in chemoreception for host plant recognition.     

Mating behavior and male mating success in wildAnastrepha Ludens (Diptera: Tephritidae) on a field-caged host tree

Mating behavior and factors affecting mating success of males were studied using wild Anastrepha ludens on a fieldcaged host tree. The most common courtship sequence had five components: (1) male calls from the underside of a leaf, (2) female arrives to the maleoccupied leaf, (3) male orients to female and stops calling, (4) one or both approach to a face-to-face position 1–3 cm apart, and (5) male mounts female after 1–2 s. Courtship behavior was almost identical to that of laboratoryculture flies observed previously under laboratory conditions. Most malefemale encounters occurred at a height of 1–2m, well inside the outer canopy of the tree. Differential mating success by males occurred. No male mated more than once per day, owing possibly to a very short sexual activity period. Factors favoring mating success of males were survival ability and tendency to join male aggregations and to fight other males. Thorax length and age (9–11 days difference) had no effects on male copulatory success. Overall win/loss percentage was not related to mating success because the males that were most successful at mating fought mostly among themselves, driving their win/loss percentage down. However, these successful males (at mating) won most of their fights against less successful males. Results confirmed a lek mating system: males aggregated, called, and defended territories; territories did not contain femalerequired resources; and females exercised mate choice, apparently through selection of sites within leks.     

Trade-offs between constitutive and induced resistance in wild crucifers shown by a natural,but not an artificial,elicitor

Constitutive and induced plant resistance against herbivores occurs throughout the plant kingdom, but little is known about the evolutionary relationship between these two types of resistances. We examined the relationships between constitutive and induced resistance to the diamondback moth, Plutella xylostella, in 11 wild species of crucifers, and analyzed the changes in volatiles associated with their expression in two species. We used larvae of P. xylostella and jasmonic acid (JA) as elicitors of the induced response. The level of resistance was estimated as the relative number of eggs laid on the plants by P. xylostella. Substantial variation in constitutive resistance was observed among the 11 crucifer species. When the plants were damaged by larvae, a negative correlation was found between constitutive and induced resistance. However, a positive correlation was detected between constitutive and induced resistance when the plants were treated by JA. The shift in resistance was associated with changes in the emission of volatiles. These results strongly suggest that (1) a trade-off occurs between constitutive and induced resistance in wild crucifers, and that (2) such a trade-off can be observed by treating the plants with a natural, but not an artificial, elicitor.     

Effect of temperature and host tree on cold hardiness of hemlock looper eggs along a latitudinal gradient

The hemlock looper, Lambdina fiscellaria, is an economically important insect pest of Canadian forests which overwinters as eggs. Although the hemlock looper causes extensive damages, no information on the mechanisms related to its cold tolerance is known. The objective of this study was to determine the effect of temperature and exposure duration on hemlock looper winter survival but also to identify seasonal supercooling capacity and cryoprotectant levels of three populations along a latitudinal gradient. As host plant may contribute to offspring overwintering success, cold tolerance of hemlock looper eggs from parents whose larvae were fed on three different tree species was also measured. Mean supercooling point (SCP) of hemlock looper eggs was lower than −30 °C from October through the following spring with values being as low as −47 °C in February. Trehalose was the most abundant sugar found in hemlock looper eggs with a peak concentration of 0.3 μg mg⁻¹ DW⁻¹. Glycerol, a polyol, was more often absent in eggs of the different populations and tree species tested in the study. When exposed to different temperature regimes for various periods of time, significant mortality of hemlock looper eggs occurred at higher temperatures than the mean SCP. Thus, hemlock looper could be considered as a chill tolerant species. No clear pattern of population and host plant effects on SCP and cryoprotectants was detected in this study. However, when exposed to different winter temperatures and exposure duration, hemlock looper from higher latitudes survived better (survival rates ranging between 0 and 89% at −20 °C) than those from lower latitudes (survival rates ranging between 0 and 56% at −20 °C). Our results may contribute to a better understanding of hemlock looper winter biology and thus facilitate predictions of outbreaks and range expansion.     

The effects of host plant defoliation and fertilizer application on larval growth and oviposition behaviour in cinnabar moth

Summary Defoliated ragwort plants produced regrowth foliage that was higher in alkaloid, but lower in amino acid concentrations than primary foliage. Total N was not affected. 2) Plants fertilized with nitrogen (as ammonium sulphate) had lower amino acid concentrations than unfertilized control plants, slightly increased alkaloid levels but similar total N concentrations. 3) Ovipositing females laid eggs upon plants with equal probability for controls, regrowth and fertilized foliage (one rosette in 5 received an egg batch). However, the probability of receiving eggs was significantly lower on the primary leaves of cut-back plants that had had their lower leaves removed a few days before egg laying (only one rosette in 13 was selected). 4) Egg batch size was higher on fertilized control foliage than on other treatments. 5) Larvae attained greater final weights when fed a diet of regrowth foliage, despite the higher levels of alkaloid they contained. Larval development rate was not affected by experimental treatment of the foliage. 6) Larval growth was lowest on the leaves of fertilized plants. This was associated with significant reductions in the concentrations of three amino acids (methionine down 29%, tyrosine 33% and lysine 25%).     

Transient host paralysis as a means of reducing self-superparasitism in koinobiont endoparasitoids

The term ‘idiobiont’ refers to those parasitoid species that permanently paralyse their hosts during parasitism, causing the cessation of host growth and development. This is in contrast to koinobiont parasitoids, which allow their hosts to continue developing after being parasitized. While no koinobiont species induce permanent paralysis in their hosts, a minority of koinobionts induce a temporary paralysis that does not interfere with overall host growth and development. We characterized transient paralysis induction in two koinobiont aphid parasitoids in the genus Binodoxys (Hymenoptera: Aphidiinae). Both Binodoxys species induced transient paralysis in Aphis glycines, with paralysis time ranging between 4.5 and 8 min (depending upon parasitoid species and host instar). In a separate experiment, B. communis was capable of inducing transient paralysis in nine aphid species. We addressed two hypotheses potentially explaining the adaptive value of temporary host paralysis in experiments using A. nerii, which is readily accepted but engages in strong defensive behaviour. The first hypothesis is that paralysis increases oviposition success by interfering with host defences and the second is that it aids in the avoidance of self-superparasitism. Paralysed aphids were more likely to be rejected by B. communis than were aphids that had never been stung or that had recovered from paralysis. This result supports the avoidance-of-self-superparasitism hypothesis and is inconsistent with the hypothesis that transient paralysis increases oviposition success of B. communis.     

Fitness consequences of host use in the field: temporal variation in performance and a life history tradeoff in the moth <Emphasis Type="Italic">Rothschildia lebeau</Emphasis> (Saturniidae)

That fitness varies as a function of using different hosts is a basic premise of theory addressing the ecology and evolution of oviposition behavior and host selection. Few data exist demonstrating: (1) the effects of different hosts on fitness in the field, and (2) how these effects vary spatially or temporally. Cohorts of caterpillars were followed from hatching to adulthood to test the hypotheses that: (1) hosts have significant effects on herbivore performance in nature, and (2) host "quality" for performance varies predictably (i.e., the rank order is consistent) across herbivore generations. In total, the fates of >2,000 caterpillars were followed on 238 individual host trees. Host species had significant effects on most, but not all, measured components of caterpillar performance in the field. Variation among generations was mainly quantitative rather than qualitative, with few changes in the rank order of hosts in their effects on performance. There was also a strong seasonal effect on performance such that caterpillar growth and survival were higher in the early wet season compared to the late wet season. Using estimates derived from these data, correlations among larval growth rate, larval survival, total development time, and final adult size were examined at the level of host plant species. Across generations, larval survival was consistently poor, development time was long, but final adult size attained was large on the host Spondias mombin. The converse was true for the host Exostema mexicanum. Relative performance on the host Casearia nitida was variable between the other two hosts. Overall, the data suggest that host use involves a predictable tradeoff between larval survival and final adult size, but argue that which is the "better" host from the female perspective will depend on the fitness consequences of producing a few, relatively large offspring versus producing more, relatively small offspring.