Asian chestnut gall wasp in Tuscany: gall characteristics,egg distribution and chestnut cultivar susceptibility

• 1 Preliminary investigations were carried out on Dryocosmus kuriphilus Yasumatsu on Castanea sativa Miller in Tuscany to assess variations in gall characteristics in coppice and high forest at two crown heights (height < 2 or 2–6 m), influence of bud size and bud position on oviposition rates and susceptibility of three cultivars.
• 2 Gall size may depend on various factors, including wasp population density. In the present study area, small galls (with one or two cells) were the most numerous in 2008, whereas larger galls (with more than three cells) prevailed in 2009.
• 3 Dryocosmus kuriphilus oviposition occurrence was influenced by both bud size and bud position. Buds with eggs tended to be larger in size compared with bud without eggs, suggesting that D. kuriphilus females prefer to lay eggs in larger buds (approximately 6 mm³) compared with smaller buds (approximately 3 mm³). The mean number of eggs per bud tended to decrease from the apical bud toward the basal bud.
• 4 Three C. sativa cultivars, Carpinese, Fusca and Cesurone, were examined. Fusca grafts had significantly more galls compared with Carpinese and Cesurone, whereas Cesurone grafts had more larvae per bud compared with Carpinese and Fusca. Overall, the Carpinese cultivar may be less susceptible to D. kuriphilus galling compared with the Fusca and Cesurone cultivars.

     

Influence of the introduced parasitoid Torymus sinensis (Hymenoptera: Torymidae) on T. koreanus and T. beneficus as indigenous parasitoids of the chestnut gall wasp Dryocosmuskuriphilus (Hymenoptera: Cynipidae) on chestnut trees in Nagano Prefecture, Japan

We describe here the parasitoid wasps Torymus sinensis Kamijo and T. beneficus Yasumatsu & Kamijo (early-spring and late-spring strains), which are introduced and indigenous natural enemies of the chestnut gall wasp Dryocosmus kuriphilus Yasumatsu, an invasive chestnut pest in Japan. We recently discovered specimens of T. koreanus Kamijo, endemic in Korea, among Torymus parasitoids collected from D. kuriphilus galls in a Japanese chestnut orchard. In this study we compare the composition of Torymus parasitoids emerging from D. kuriphilus galls before and after the release of T. sinensis. Before the release of T. sinensis, early-spring and late-spring strains of T. beneficus predominated (58.3 and 20.8% of specimens collected). However, a few years after the release, both T. beneficus strains had been almost completely displaced by T. sinensis. In contrast to the rapid decrease in T. beneficus, T. koreanus did not decrease drastically before and even after the release of T. sinensis (approximately 10–20% of specimens collected). These results suggest that not a few T. koreanus were present in the Japanese chestnut orchard investigated at least several years after the release of T. sinensis, although both the T. beneficus strains were rapidly displaced by T. sinensis during this period.     

Optimal clutch size of the chestnut gall-wasp,Dryocosmus kuriphilus yasumatsu (Hymenoptera: Cynipidae)

Optimal clutch size of the chestnut gall-wasp, Dryocosmus kuriphilus Yasumatsu (Hymenoptera: Cynipidae), was examined in galls on wild and resistant chestnut trees in 1988 and 1989. The rate of escape success of newly-emerged adults from galls was an average of 60%, irrespective of cell numbers per gall. Dry mass per cell of a gall (as an index of nutritive condition) decreased with increasing cell number per gall, but was proportional to the mean number of mature eggs of new adults per gall. The number of cells per gall that occurred most frequently did not agree with that attained by the maximum survival rate from young larva to adult emergence of the gall-wasp. This discrepancy was examined from the viewpoint of three factors: 1) quality of offspring, 2) defensive response of the host plant causing mortality of the gall-wasp before cell formation, and 3) fitness per gall vs. fitness per egg. It is concluded that the third factor is most likely to be the one best in explaining the discrepancy.     

Wolbachia prevalence patterns: horizontal transmission,recombination, and multiple infections in chestnut gall wasp-parasitoid communities

The Oriental chestnut gall wasp, Dryocosmus kuriphilus Yasumatsu (Hymenoptera: Cynipidae), is a global invasive pest that causes serious damage to almost all chestnut species belonging to the Castanea genus (Fagaceae). Dryocosmus zhuili Liu et Zhu is a recently described sibling species of D. kuriphilus, which induces galls on Castanea henryi (Skan) Rehd. et Wils. There are many indigenous parasitoid species in China which play an important role in the natural regulation of their population dynamics. Wolbachia is a maternally inherited α-proteobacterium widely found in arthropods. This study screened for the presence of Wolbachia in the two chestnut gall wasps and in six parasitoid species from 12 populations, to investigate the prevalence patterns of Wolbachia in the chestnut gall wasp-parasitoid communities. We found that D. zhuili and four parasitoid species were infected with Wolbachia; among them, all individuals of the two populations of Megastigmus sp. had multiple Wolbachia infections. By using multilocus sequence types to characterize bacterial strains, three new sequence types were identified. The Wolbachia strains infecting D. zhuili (ST-507), Torymus sinensis Kamijo (ST-508), and Sycophila variegata (Curtis) (ST-508) belonged to supergroup A, whereas the Wolbachia strain infecting Megastigmus nipponicus Kamijo (ST-503) belonged to supergroup B. Our results also suggested that horizontal transmission of Wolbachia occurs between chestnut gall wasps and their parasitoids. Moreover, multiple Wolbachia infections of Megastigmus sp. may be due to gene recombination and horizontal transmission.     

No loss of genetic divergence in Torymus sinensis following its release for Dryocosmus kuriphilus control in Europe

1. Arrival, establishment, and further dispersal of non-native natural enemies are considered essential for a successful biological control programme, while among the factors that may determine the success of such a programme, genetic diversity of the introduced population plays an important role in the establishment of a non-native species.
2. The Chinese parasitoid wasp Torymus sinensis Kamijo (Hymenoptera: Torymidae) was initially released in Europe in Italy to control biologically the Asian chestnut gall wasp Dryocosmus kuriphilus Yasumatsu (Hymenoptera: Cynipidae), and reduce the damage induced on sweet chestnut (Castanea sativa Miller). In the following years, T. sinensis was then released in numerous other European countries as a biological control agent of D. kuriphilus. Its presence has also been reported beyond the countries of release due to rapid natural dispersal.
3. To assess the post-release genetic diversity of D. kuriphilus, we screened T. sinensis populations from six European countries and tested the possibility of these populations suffering from frequently observed genetic effects that could threaten its successful establishment in Europe.
4. Our results exhibit that T. sinensis populations have suffered neither from the Allee effect nor from genetic bottleneck after their release and establishment in Europe, something that increases the possibility to effectively control D. kuriphilus in Europe.

     

Temperature,size, reproductive allocation,and life‐history evolution in a gregarious caterpillar

The present study aimed to investigate the relationship between growth rate, final mass, and larval development, as well as how this relationship influences reproductive trade‐offs, in the context of a gregarious life‐style and the need to keep an optimal group size. We use as a model two sympatric populations of the pine processionary moth Thaumetopoea pityocampa, which occur in different seasons and thus experience different climatic conditions. Thaumetopoea pityocampa is a strictly gregarious caterpillar throughout the larval period, which occurs during winter in countries all over the Mediterranean Basin. However, in 1997, a population in which larval development occurs during the summer was discovered in Portugal, namely the summer population (SP), as opposed to the normal winter population (WP), which coexists in the same forest feeding on the same host during the winter. Both populations were monitored over 3 years, with an assessment of the length of the larval period and its relationship with different climatic variables, final mass and adult size, egg size and number, colony size, and mortality at different life stages. The SP larval period was reduced as a result of development in the warmer part of the year, although it reached the same final mass and adult size as the WP. Despite an equal size at maturity, a trade‐off between egg size and number was found between the two populations: SP produced less but bigger eggs than WP. This contrasts with the findings obtained in other Lepidoptera species, where development in colder environments leads to larger eggs at the expense of fecundity, but corroborates the trend found at a macro‐geographical scale for T. pityocampa, with females from northern latitudes and a colder environment producing more (and smaller) eggs. The results demonstrate the importance of the number of eggs in cold environments as a result of an advantage of large colonies when gregarious caterpillars develop in such environments, and these findings are discussed in accordance with the major theories regarding size in animals. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 340–349.     

The problem of optimal clutch size in a tritrophic system: the oviposition strategy of the thistle gallfly Urophora cardui (Diptera,Tephritidae)

The problem of optimal clutch sizes is a central theme in life history theory. Optimal allocation of eggs is especially complicated for insects in tritrophic systems. In this study we analyze some of the processes determining clutch sizes of the thistle gallfly Urophora cardui, a monophagous tephritid fly associated with Cirsium arvense. U. cardui forms multilocular shoot galls, which vary broadly in their size and number of their gall cells. We investigate various fitness consequences of gall size. An analysis of the number of cells per gall (which is correlated with gall diameter and gall weight) showed that in U. cardui there is mutual facilitation rather than larval competition. Increasing numbers of larvae per gall led to a decreasing mortality and increasing larval weight. Larval weight in turn was positively correlated with the probability of survival to adulthood and with adult weight and fecundity. Thus, all fitness parameters measured favoured large galls. Clutch sizes in oviposition experiments were distinctly larger than the number of gall cells of field populations and in cage experiments, suggesting high mortality of eggs and/or early larval instars. There was a significant relationship between the internal structure (i.e., the size of the growing point) of the bud and clutch size, suggesting that U. cardui females are able to measure bud quality and adapt clutch sizes accordingly. Clutch size was positively correlated with the female's age at first oviposition and negatively with the number of previous ovipositions and previously laid eggs. Since the potential egg capacity per female is higher than the average number of larvae it is likely to produce during its short adult lifespan, U. cardui females tend to be time-limited rather than egglimited, which might favour large clutches once an appropriate oviposition site has been located. As the development of the gall and hence the fate of a clutch depends on a number of unpredictable factors, exclusive concentration of eggs in a few large clusters would involve risks which could be avoided by increasing the number of clutches. Therefore we interpret the high variation of clutch sizes in U. cardui as a mixed strategy of bet hedging and gambling.     

Clutch size manipulations in the chestnut weevil, Curculio elephas: fitness of oviposition strategies

We test the adaptive value of clutch size observed in a natural population of the chestnut weevil Curculio elephas. Clutch size is defined as the number of immatures per infested chestnut. In natural conditions, clutch size averages 1.7 eggs. By manipulating clutch size in the field, we demonstrate that deviations from the theoretical ”Lack clutch size”, estimated as eight immatures, are mainly due to proximate and delayed effects of clutch size on offspring performance. We show the existence of a trade-off between clutch size and larval weight. The latter, a key life-history trait, is highly correlated with fitness because it is a strong determinant of larval survival and potential fecundity of offspring females. The fitness of different potential oviposition strategies characterized by their clutch sizes, ranging from one to nine immatures, was calculated from field- estimated parameters. Chestnut weevil females obtain an evolutionary advantage by laying their eggs singly, since, for instance, fitness of single-egg clutches exceeds fitness of two-egg clutches and four-egg clutches by 8.0% and 15.1% respectively. Received 4 August 1999 / Accepted: 7 October 1999     

Population dynamics of the chestnut gall-wasp,Dryocosmus kuriphilus Yasumatsu (Hymenoptera: Cynipidae)

Summary As a part of serial study on population dynamics of the chestnut gall-wasp,Dryocosmus kuriphilus, analyses of the distribution of eggs, gall-cells and emergent holes were made from the statistical point of view. Many of distributions of the eggs per bud could be described by the truncated Poisson, but some cases showed slight overdispersion than expected by chance. Because of no linear increase of with increasing (expected mean for complete sample), however, the truncated negative binomial seemed to be not so available for whole series. Distributions of the gall-cells and the emergent holes were, on the other hand, well described by the truncated Poisson distribution when the observed frequency was calculated for respective trees. Negative-binomial tendency found in distributions from some stations consisted of a certain number of trees would be resulted from mixture of Poisson populations with different means. Random or slightly concentrated oviposition and random mortality within galls was thus supposed for future study unless the proof favouring other distribution models would appear.     

Effect of changes in resource level on age and size at metamorphosis in Hyla squirella

Recent experiments suggest that timing of metamorphosis is fixed during development in some anurans, insects, and freshwater invertebrates. Yet, these experiments do not exclude a growth rate optimization model for the timing of metamorphosis. I manipulated food resources available to larvae of squirrel treefrogs (Hyla squirella) to determine if there is a loss of plasticity in duration of larval period during development and to critically test growth rate models for the timing of metamorphosis. Size-specific resource levels for individual tadpoles were switched from low to high or high to low at three developmental stages spaced throughout larval development. The effects of changes in resource availability on larval period and mass at metamorphosis were measured. Switching food levels after late limb bud development did not significantly affect larval period in comparison to constant food level treatments. Therefore, developmental rate in H. squirella is better described by a fixed developmental rate model, rather than a growth rate optimization model. The timing of fixation of developmental rate in H. squirella is similar to that found in other anuran species, suggesting a taxonomically widespread developmental constraint on the plasticity of larval period duration. Mass at metamorphosis was not significantly affected by the timing of changes in food levels; the amount of food available later in development determined the size at metamorphosis. Larval period and mass at metamorphosis were negatively correlated in only one of two experiments, which contrasts with the common assumption of a phenotypic trade-off between decreased larval period and increased mass at metamorphosis. Received: 19 August 1996 / Accepted: 20 June 1997     

Egg maturation and oviposition strategy of a capital breeder,Cleorodes lichenaria,feeding on lichens at the larval stage

Abstract 1. Capital breeders rely solely on resources acquired before breeding, whereas income breeders may obtain considerable amounts of resources following the commencement of reproduction. In income breeders oviposition occurs over a longer time period with a small number of eggs ready to be laid at the start of adult life, whereas capital breeders reproduce more rapidly and contain higher numbers of mature eggs at eclosion relative to potential fecundity. 2. This study explored egg maturation and oviposition strategy of a nocturnal geometrid moth, Cleorodes lichenaria. It was predicted, based on the long larval period of C. lichenaria and the known biology of other geometrids, that this lichen‐feeding geometrid moth concentrates egg production at the beginning of its breeding period and that external nutrients have a limited role on its fecundity. 3. Approximately 46% of eggs were ready to be laid in newly hatched females and approximately 40% of their potential fecundity was realised during the first night, after which the number and the weight of eggs decreased steadily. Feeding or drinking did not increase the fecundity of females. Pupal mass correlated positively with realised fecundity and ovigeny index. 4. Reproduction of C. lichenaria is based solely on larval‐derived resources. It is suggested that females are able to resorb thoracic tissues to increase fecundity and that this ability is probably linked to relatively long lifespan and low ovigeny index of this species, characteristics rarely observed in other geometrid moths.     

<Emphasis Type="Italic">Torymus sinensis</Emphasis>: a viable management option for the biological control of <Emphasis Type="Italic">Dryocosmus kuriphilus</Emphasis> in Europe?

The chestnut gall wasp Dryocosmus kuriphilus is a global pest of chestnut (Castanea spp). Established as a pest in the mid-twentieth century in Japan, Korea and North America, this species was first reported in Europe in 2002. Following the successful release of a biological control agent Torymus sinensis in Japan, this parasitoid species has been released in Italy since 2005. Here we discuss the potential of T. sinensis as a viable management option for the biological control of D. kuriphilus in central Europe. We suggest that more consideration should be given to determining, (i) the conditions under which T. sinensis may attack alternative native gall wasp hosts and (ii) the likelihood of hybridization of this species with native Torymus. Both issues are central to predicting unassisted range expansion by released T. sinensis, and to assess the environmental risks associated with a more widespread release of this species in Europe.     

Population dynamics of the chestnut gall-wasp,Dryocosmus kuriphilus Yasumatsu (Hymenoptera: Cynipidae) IV. Further analysis of the distribution of eggs and young larvae in buds using the truncated negative binomial series

Distribution pattern of eggs and the first instar larvae of the chestnut gall-wasp, Dryocosmus kuriphilus, per bud of the chestnut tree was re-examined using the truncatedPoisson and the truncated negative binomial series. The results are as follows:

1. About sixty percent of the distribution are approximated by the truncated negative binomial and another thirty percent by the truncatedPoisson . When the distribution has been approximated by the truncated negative binomial, the show scattered values, some of which are near thePoisson , but the mean value of is about 4 both in eggs and in the first instar larvae.
2. The number of buds which have not been infested by gall-wasps is resulted from various factors as follows: (a) Buds formed after the laying activity of gall-wasps has ceased; (b) Old and shrunk buds which were avoided in laying; (c) Buds in which eggs have died by the time of sampling; and (d) Buds escaping ovipositions by chance. Most of the gall-wasp-free buds located in the middle part of the shoot are accounted for the zero-class expected by the negative binomial series.
3. Brass (1958) moment method for estimating parameters of the truncated negative binomial give good precision within the range of from 1 to 10 and of from 1 to 6.
4. It is concluded that the truncated distributions used are useful for the purpose of analysis of the distribution pattern of the chestnut gall-wasp.

     

Life-history studies of Lydella jalisco (Diptera: Tachinidae), a parasitoid of Eoreuma loftini (Lepidoptera: Pyralidae)

Lydella jalisco Woodley (Diptera: Tachinidae) is a solitary endoparasitoid of the Mexican rice borer, Eoreuma loftini (Dyar) (Lepidoptera: Pyralidae), the key pest of sugarcane in Texas. This parasitoid was re-introduced into Texas in 1998 as part of a classical biological control program. Information on the biology of L. jalisco is scarce and indispensable for its propagation in captivity and understanding of L. jalisco-E. loftini interactions. Parasitoid longevity, reproductive biology and immature development were studied under laboratory conditions. At 22 °C, honey-fed mated adults lived about two weeks whereas lifespan of unmated individuals averaged three weeks. Females of L. jalisco emerged with a complement of eggs that continued to develop during the first days following emergence. Mating was necessary for embryonic development. After copulation, eggs were fertilized and gradually transferred to an elongated ovisac where they incubated for about one week before hatching. Hatching occurred in the female's reproductive tract, an attribute of true ovoviviparous reproduction. First instar larvae were available for oviposition during the female's entire lifetime. Egg load increased with adult female size; mean lifetime potential fecundity was 400 ± 140 eggs per female. Parasitoids successfully developed on second to sixth instar host larvae. However, host size at parasitization positively influenced the size of resultant adult parasitoids as well as the duration of the larval growth period which was shorter as host size increased. Parasitoid larvae did not complete development below 15 °C, whereas parasitoid larval and pupal mortality respectively reached 14 and 75 percent when temperature exceeded 30 °C. The importance of biological and reproductive attributes of L. jalisco for biological control, as well as for rearing are discussed.     

Carbohydrate metabolism in one- and two-year-old spruce needles, and stem carbohydrates from three months before until three months after bud break

Starch and sucrose metabolism of one- and two-year-old needles of Norway spruce (Picea abies [L.] Karst., about 30 years old) was investigated from three months before until three months after bud break at a natural site. We distinguish different metabolic states according to the extractable activities of enzymes (α-amylase [EC 3.2.1.1], ADP-glucose pyrophosphorylase [AGP, EC 2.7.7.27], D-enzyme [EC 2.4.1.25], starch phosphorylase [STP. EC 2.4.1.1]), sucrose phosphate synthase [SPS, EC 2.4.1.14], sucrose syntbase [SS, EC 2.4.1.13]. acid invertase [AI, EC 3.2.1.261) and pool sizes of related metabolites (starch, glucose, fructose, sucrose, raffinose, stachyose, fructose 6-phosphate [F6P], glucose 6-phosphate [G6P], fructose 2,6-bisphosphate [F26BP], and inorganic phosphate [P₁]). The period ending with bud break was characterized by high rates of net photosynthesis, a pronounced decrease in the amount of soluble sugars, and a steep rise in starch (from the detection limit to approximately 600 nmol glycosyl units [mg dry weight]_-1). In parallel, the extractable activity of AGP increased, while D-enzyme was on a relative high level when compared with the period after bud break. With respect to sucrose metabolism, F26BP, an inhibitor of sucrose synthesis, decreased from 1 to 0.4 pmol (mg dry weight)_-1. This was complemented by SPS activity, which was due to both increased protein levels shown by immunoblotting and activation under metabolite control (high levels of G6P and a low P_i/G6P ratio). This indicates a high capacity of synthesis of starch and sucrose in the period before bud break. These observations are in accordance with estimates of photosynthetic carbon gain, which indicate that in early spring large amounts of carbon from current photosynthesis are exported out of the needles. In addition, the content of nonstructural carbohydrates (expressed as hexoses) increased in the bark of the stem. This could also be a consequence of an enhanced carbon export from the needles. After the onset of bud break, starch concentration decreased in all tissues under investigation. In contrast, the level of total nonstructural carbohydrates in the outermost sapwood nearly doubled from bud break until the end of sampling. In the needles, net photosynthesis was reduced by about 75% and a decrease in SPS activity and protein level were found together with lower G6P concentration, and an increased P_i/G6P ratio. These results suggest that during that period sucrose synthesis was reduced in the older needles. In addition, under conditions of reduced photosynthesis, carbon demand of current year needles was in part ensured by the mobilization of starch in the older needles. Taken together our data show that before bud break carbon metabolism of mature leaves is related with the sink demands of storage organs. After bud break the accumulated assimilate pools in needles and stem, mainly the bark, are mobilized and support carbon supply to new tissues.     

Early spring defoliation,secondary leaf flush,and leafminer outbreaks on American holly

Summary Adults of Phytomyza ilicicola (Diptera: Agromyzidae), a univoltine specialist leafminer, emerge in close synchrony with leaf flush of American holly and feed on and oviposit in soft, partially expanded leaves. Early spring defoliation, such as commonly results from freezing injury to young shoots, is followed several weeks later by a second flush of young leaves from lateral buds. We simulated this phenomenon by manually defoliating whole small trees and individual shoots of large trees to test the hypothesis that freezing injury can encourage leafminer outbreaks by inducing an abundance of soft, protein rich young leaves late in the adult activity period, when availability of vulnerable leaves becomes limited. Defoliation of small trees one or two weeks after bud break resulted in six- to 13-fold increases in the incidence of feeding punctures and larval mines on second flush leaves as compared with densities on original young leaves of control trees. Similarly, we induced significant increases in feeding punctures and larval mines on second flush leaves of individual defoliated shoots, although leaves that did not open until after the flight period escaped this injury. These observations underscore the capability of adult female P. ilicicola to locate and exploit a small number of phenologically available leaves among many hundreds of older leaves on the same tree. By altering the phenology of leaf flush, certain kinds of environmental stress may predispose perennial plants to outbreaks of early season folivores that restrict their feeding or oviposition to very young leaves.     

Testing ecological interactions between Gnomoniopsis castaneae and Dryocosmus kuriphilus

An emerging nut rot of chestnut caused by the fungus Gnomoniopsis castaneae was reported soon after the invasion of the exotic gall wasp Dryocosmus kuriphilus in Italy. The goal of this work was to assess the association between the spread of the fungal pathogen and the infestation of the pest by testing if:I) viable inoculum of G. castaneae can be carried by adults of D. kuriphilus;II) the fungal colonization is related to the number of adults inhabiting the galls;III) the fungal colonization of chestnut buds and the oviposition are associated.Fungal isolations and PCR-based molecular assays were performed on 323 chestnut galls and on their emerging D. kuriphilus adults, whose number was compared between galls colonized and not colonized by G. castaneae. To test the association between fungal colonization and oviposition, Monte Carlo simulations assuming different scenarios of ecological interactions were carried out and validated through isolation trials performed on 597 and 688 chestnut buds collected before and after oviposition, respectively.Although DNA of G. castaneae was detected in a sample of 40% of the adults developed in colonized galls, the fungus could never be isolated from insects, suggesting that the pest is an unlikely vector of viable inoculum.On average, the emerging adults were significantly more abundant from galls colonized by G. castaneae than from not colonized ones (3.76 vs. 2.54, P < 0.05), indicating a possible fungus/pest synergy.The simulations implying no interaction between G. castaneae and D. kuriphilus after fungal colonization were confirmed as the most likely. In fact, G. castaneae was present in 33.8% of the buds before oviposition, while no association was detected between fungal colonization and oviposition (odds ratio 0.98, 0.71–1.33 95% CI). These findings suggest that the fungus/pest synergy is asymmetrically favorable to the pest and occurs after oviposition.     

Population dynamics of the chestnut gall wasp,Dryocosmus kuriphilus Yasumatsu (Hymenoptera: Cynipidae)

Summary During the course of a 10-year investigation on the population dynamics of Dryocosmus kuriphilus, a rapid decrease in the number of individuals was noticed in the adult stage. To detect the role of predation by spiders in causing this high adult mortality, spiders collected from the survey station were tested for their reaction to Drycosmus antiserum. About 2050% of the spiders collected during the emergence period of D. kuriphilus reacted positively, showing that the species of Thomisidae, Argiopidae, Agelenidae and Salticidae were the important predators. The predation ratio for the total adult wasp population was estimated at 8.1% in 1968, 20.2% in 1969 and much higher in 1970, increasing with decreasing population density of the wasps. However, the predation by spiders could not account for all of the adult mortality of D. kuriphilus.     

EVOLUTIONARY LOSS OF LARVAL FEEDING: DEVELOPMENT,FORM AND FUNCTION IN A FACULTATIVELY FEEDING LARVA,BRISASTER LATIFRONS

Species with large eggs and nonfeeding larvae have evolved many times from ancestors with smaller eggs and feeding larvae in numerous groups of aquatic invertebrates and amphibians. This change in reproductive allocation and larval form is often accompanied by dramatic changes in development. Little is known of this transformation because the intermediate form (a facultatively feeding larva) is rare. Knowledge of facultatively feeding larvae may help explain the conditions under which nonfeeding larvae evolve. Two hypotheses concerning the evolutionary loss of larval feeding are as follows: (1) large eggs evolve before modifications in larval development, and (2) the intermediate form (facultatively feeding larva) is evolutionarily short-lived. I show that larvae of a heart urchin, Brisaster latifrons, are capable of feeding but do not require food to complete larval development. Food for larvae appears to have little effect on larval growth and development. The development, form, and suspension feeding mechanism of these larvae are similar to those of obligate-feeding larvae of other echinoids. Feeding rates of Brisaster larvae are similar to cooccurring, obligate-feeding echinoid larvae but are low relative to the large size of Brisaster larvae. The comparison shows that in Brisaster large egg size, independence from larval food, and relatively low feeding rate have evolved before the heterochronies and modified developmental mechanisms common in nonfeeding echinoid larvae. If it is general, the result suggests that hypotheses concerning the origin of nonfeeding larval development should be based on ecological factors that affect natural selection for large eggs, rather than on the evolution of heterochronies and developmental novelties in particular clades. I also discuss alternative hypotheses concerning the evolutionary persistence of facultative larval feeding as a reproductive strategy. These hypotheses could be tested against a phylogenetic hypothesis.     

Effects of embryo energy,egg size,and larval food supply on the development of asteroid echinoderms

Organisms have limited resources available to invest in reproduction, causing a trade‐off between the number and size of offspring. One consequence of this trade‐off is the evolution of disparate egg sizes and, by extension, developmental modes. In particular, echinoid echinoderms (sea urchins and sand dollars) have been widely used to experimentally manipulate how changes in egg size affect development. Here, we test the generality of the echinoid results by (a) using laser ablations of blastomeres to experimentally reduce embryo energy in the asteroid echinoderms (sea stars), Pisaster ochraceus and Asterias forbesi and (b) comparing naturally produced, variably sized eggs (1.7‐fold volume difference between large and small eggs) in A. forbesi. In P. ochraceus and A. forbesi, there were no significant differences between juveniles from both experimentally reduced embryos and naturally produced eggs of variable size. However, in both embryo reduction and egg size variation experiments, simultaneous reductions in larval food had a significant and large effect on larval and juvenile development. These results indicate that (a) food levels are more important than embryo energy or egg size in determining larval and juvenile quality in sea stars and (b) the relative importance of embryo energy or egg size to fundamental life history parameters (time to and size at metamorphosis) does not appear to be consistent within echinoderms.