Orientation of flight for physically disturbed spotted lanternflies,Lycorma delicatula, (Hemiptera,Fulgoridae)

The spotted lanternfly, Lycorma delicatula, (Hemiptera, Fulgoridae) is an invasive pest to Korea and the United States, originating from China or Southeast Asia. Immature L. delicatula feed on a wide range of plants, but the adults are more host-selective, often preferring the tree of heaven, Ailanthus altissima. We performed field studies to evaluate adult movement in relation to A. altissima after disturbance. The Ailanthus trees were in a mixed suburban forested situated at the southern border of an open grassy field. Female adult lanternflies were manually disturbed from feeding on the trunks of large A. altissima trees. In the first experiment, insects were disturbed directly from the tree using a ballpoint pen to simulate a predatory attack. These insects usually flew initially southward away from the tree line toward a sunlit field, but turned northward back toward the tree line. In the second experiment, to simulate an initially successful predatory attack, they were manually taken from trees, and allowed to escape. The females immediately opened their wings in an apparent aposematic display. They then either immediately flew toward the sunlit open field, or remained with their wings splayed open for a prolonged period.     

Sex and tree rings: Females neither grow less nor are less water-use efficient than males in four dioecious tree species

Females of woody dioecious species usually expend more resources on reproduction than males. Therefore, it is expected that females incur greater costs of reproduction than males, and, as a result, trade-offs between reproduction and growth should emerge. The aim of this study is to test those hypotheses by analyzing the differences between genders regarding radial growth (basal area increment) and wood carbon isotope composition (δ¹³C), a proxy of water-use efficiency. We compared these two variables in males and females of four dioecious tree species inhabiting drought-prone Mediterranean sites in Spain (Pistacia terebinthus, Ilex aquifolium, Juniperus thurifera and Ailanthus altissima). We analyzed the influence of sex on the radial growth patterns throughout the tree life considering the growth stage of individuals, the differences in the response of genders to climate variables (air temperature, precipitation and drought severity), and the δ¹³C during a severe drought period. One site was studied for each species and 21–33 trees per species were sampled in each site. No differences in growth were found between genders for any of the four species throughout their life span. No significant interactions between gender and precipitation were found, although A. altissima males were more responsive to summer (June-July) temperature. No differences in δ¹³C were found between genders excepting for P. terebinthus, indicating that the males of this species show a less efficient water use during drought events than the females. These results do not support the broad assumption that females of woody dioecious plants show lower growth and are less water-use efficient than males or that they respond differently to precipitation variability, except for P. terebinthus during drought events. Further analyses could be performed in other dioecious species inhabiting seasonally dry regions to confirm or reject our conclusions.     

GENETIC DIFFERENTIATION AMONG HOST-ASSOCIATED POPULATIONS OF THE GALLMAKER EUROSTA SOLIDAGINIS (DIPTERA: TEPHRITIDAE)

Eurosta solidaginis, a gallmaking tephritid (Diptera), infests at least two species of Solidago in the eastern United States. We used horizontal starch gel electrophoresis of enzymes to examine whether populations on the two principal host plant species, Solidago altissima and S. gigantea, have diverged genetically. At the d -β-hydroxybutyrate dehydrogenase (HBDH) locus, the predominant allele in all nine populations from S. altissima (HBDH^1.00) was absent or uncommon in all but 1 of the 12 populations from S. gigantea. At the phosphoglucomutase locus (PGM), the most common allele in all populations was PGM^1.00, but the frequency of this allele was, with one exception, higher in populations from S. gigantea than in populations from S. altissima. Genetic heterozygosity was usually greater in populations from S. altissima (H? = 0.028) than in populations from S. gigantea (H? = 0.009). A phylogenetic tree derived from a genetic distance matrix clustered gallmaker populations from the same host plant together.     

高榕榕果内Eupristina属两种榕小蜂的遗传进化关系

对生长在福州地区的高榕进行长期追踪观察,发现高榕榕果内仅生活着Eupristina altissima和Eupristina sp.榕小蜂,前者为高榕的传粉小蜂,后者无传粉行为,两者雌蜂之间在体色、触角、花粉袋和花粉刷等部位存在细微的差异,而两者雄蜂之间无形态差异。通过克隆福建地区5个样地的高榕榕果内收集到的E. altissima和Eupristina sp.榕小蜂,以及细叶榕的传粉小蜂Eupristina verticillata(外群)的Cytb及COI基因,并进行碱基组成及遗传距离分析,用邻接法构建系统发育树,分析两榕小蜂群体之间的遗传进化关系,结果显示:(1)榕小蜂COI及Cytb序列碱基组成中A+T的含量(Cytb序列中A+T=75.3%,COI序列中A+T=75.5%)显著高于G+C,符合膜翅目昆虫线粒体基因碱基组成特征。(2)对两群体小蜂进行遗传距离分析显示,Cytb序列中E. altissima和Eupristina sp. 群体内各样本之间的平均遗传距离分别为0.0092和0.0030,而E. altissima与Eupristina sp. 群体间的平均距离为0.1588;COI序列中E. altissima 与Eupristina sp. 群体内各样本之间的平均遗传距离分别为0.0065和0.0205,而二者群体间的平均遗传距离为0.1043,表明两者群体间的遗传距离明显大于各自群体内各样本间的遗传距离。统计GenBank中下载的6个属34种榕小蜂Cytb序列的种间遗传距离为0.0811-0.1723,6个属28种榕小蜂COI序列的种间遗传距离为0.0939-0.1986。由此认为E. altissima和Eupristina sp.之间的遗传距离差异已经达到了种间水平,即E. altissima与Eupristina sp.为两个不同的种。(3)在形态上,两种小蜂的雌蜂之间有微小差异,而二者雄蜂之间无差异,但Cytb与COI序列分析结果一致表明:E. altissima与Eupristina sp.雄蜂之间,以及二者雌蜂之间的遗传距离均差异显著,表明形态变异滞后于基因变异。雌蜂在表型上进化快于雄蜂,可能是由于雌蜂羽化后从榕果出飞,受到外界环境因素的影响较大,且两种雌蜂在传粉功能上存在差异,故二者之间的形态差异较大,而雄蜂寿命短,又终生生活在黑暗封闭、环境变化相对恒定的榕果内,两种雄蜂在行为上不存在差异,故二者表型变异较为缓慢。E. altissima和Eupristina sp.小蜂对宿主的专一性不强,在榕-蜂协同进化过程中,可能发生过宿主转移事件。     

Progression of seasonal activities of adults of the spotted lanternfly,Lycorma delicatula,during the 2017 season of mass flight dispersal behavior in eastern Pennsylvania

During the summer and fall of 2017 in northeastern Pennsylvania we studied the progression of adult behaviors of the spotted lanternfly, Lycorma delicatula (Hemiptera: Fulgoridae) when there was an upsurge in adult flight behavior that was not known to have occurred in 2015 or 2016, the first years following its initial detection in Pennsylvania in late 2014. Sex ratios on A. altissima trunks and branches were routinely ca. 50:50 male:female throughout the 2017 season except in two instances in two of the earliest samplings in which >60% were males. Within the first week after adult eclosion in 2017, in conjunction with extensive feeding-related behaviors on Ailanthus altissima tree trunks, short flights occurred indiscriminately from the foliage of one tree to another or between bushes, trees and vines. One week later these flights became more prevalent and lengthier. Adults of both sexes launched themselves into the wind from non-host trees or from porches, posts and other human-made structures to engage in level or gradually descending straight-line flight trajectories that allowed them to traverse only usually 10 to 40 m of ground in one episode. After the peak of flight dispersal had occurred, the first mating pairs were observed on September 25. All of the 21 pairs of adults we observed in copula exhibited swollen, yellow abdomens in contrast to the thinner, predominantly black abdomens of the adults we had sampled during the earlier feeding and flight phases. Copulating pairs were observed to remain coupled for 2 to 4 h.     

Effect of volatiles emitted from wilted Populus nigra L. leaves on the mating and oviposition of Helicoverpa armigera (Hübner)

Wilted black poplar, Populus nigra ‘Italica’ L., leaves are very attractive to a vast number of noctuid moth species. This provides an opportunity for the development of effective trapping methods for the integrated management of pest species, such as Helicoverpa armigera, a major global and economically important insect pest.In the present study, we investigated the (1) nocturnal attraction patterns of H. armigera males and females to wilted P. nigra leaves; (2) effects of P. nigra volatiles on the mate-searching behavior of males through laboratory serial-chamber bioassays and field trapping; and (3) effects of P. nigra volatiles on the ovipositional choice and reproductive performance of females. Females and males, when tested alone, could be attracted by wilted P. nigra leaves, and the time periods of the first two attraction peaks were largely overlapped between sexes. Streams consisting of wilted P. nigra leaves and virgin females were not more attractive than virgin females alone, regardless of the stream sequence in a serial chamber. However, a stream of virgin females passed through wilted P. nigra leaves was more attractive than wilted P. nigra leaves alone. The addition of P. nigra extracts and its major aromatic components to the sex lure of H. armigera did not attract more moths than the sex lure alone. The volatiles from wilted P. nigra leaves were significantly more attractive to ovipositing females than those from cotton, tomato, and corn leaves, but equally attractive to tobacco leaves. Females exposed to volatiles from different leaves (P. nigra, cotton, and tobacco) showed similar fecundities. In summary, the attraction of moths to wilted P. nigra leaves may be attributable to multiple mechanisms, including the adsorption of sex pheromones, ovipostional attraction, and possible feeding attraction.     

Occurrence and development of Eucryptorrhynchus brandti and E. chinensis (Coleoptera: Curculionidae) on Ailanthus altissima trees subjected to different levels of mechanical damage

Eucryptorrhynchus brandti (Harold) and E. chinensis (Oliver) are herbivores of Ailanthus altissima (Mill.) Swingle (tree of heaven) in China. Eucryptorrhynchus brandti has been recommended as a potential biological control agent of A. altissima in North America. In China, the majority of adults of both species were found on tree trunks 0–5 m above the ground, from May to September. In October and November, most adults were found at the base of A. altissima trees. Trees were subjected to different levels of mechanical injury: very low mechanical injury, one to two 0.015 m² bark sections were removed; low, two to four bark sections were removed; moderate, 8 to 22 bark sections removed; high, tree was girdled; and extreme, tree was felled and the remaining stump was sampled. Very low and low mechanical injury trees had very few adult emergence holes with few larvae developing beyond the first or second instar after 29 months. The health of these trees remained good. An increase in adult emergence holes occurred in moderately injured trees that appeared as healthy as very low to low mechanically injured trees. This may indicate that only a small increase in tree stress can increase the adult emergence rate and thus hasten a decline in tree health. Moderate, high and extreme mechanically injured trees had significantly more emergence holes/m than very low and low injured trees and late larval stages were present. The development of Eucryptorrhynchus species was more successful the greater the degree of mechanical injury. Based on this study both Eucryptorrhynchus species appear to be secondary pests of A. altissima in China.     

Morphometrics,Illustration, and Histopathology of Sphaeronema rumicis on Cottonwood in Utah

The morphology of a population of Sphaeronema rumicis Kir''yanova found on cottonwood in Utah is illustrated by light and scanning electron micrographs, as well as by drawings. This is the first report of males of S. rumicis, a species also not known previously to occur in North America. S. rumicis females on cottonwood in the United States were smaller than those found by Kir''yanova on sorrel in the USSR. Females and second-stage juveniles (J2) from the United States had slightly shorter stylets than did females and J2 from the USSR. Males were vermiform and had degenerate esophagi. On secondary cottonwood roots S. rumicis induces formation of a syncytium originating from proliferated pericyclic cells. Thick outer walls, wall protuberances, absence of cell wall ingrowths, dense cytoplasm, and hypertrophied nuclei were the main characteristics of syncytia observed in S. rumicis-infected cottonwood roots.     

Proteomics Indicators of the Rapidly Shifting Physiology from Whole Mountain Pine Beetle,Dendroctonus ponderosae (Coleoptera: Curculionidae), Adults during Early Host Colonization

We developed proteome profiles for host colonizing mountain pine beetle adults, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae). Adult insects were fed in pairs on fresh host lodgepole pine, Pinus contorta Dougl. ex Loud, phloem tissue. The proteomes of fed individuals were monitored using iTRAQ and compared to those of starved beetles, revealing 757 and 739 expressed proteins in females and males, respectively, for which quantitative information was obtained. Overall functional category distributions were similar for males and females, with the majority of proteins falling under carbohydrate metabolism (glycolysis, gluconeogenesis, citric acid cycle), structure (cuticle, muscle, cytoskeleton), and protein and amino acid metabolism. Females had 23 proteins with levels that changed significantly with feeding (p<0.05, FDR<0.20), including chaperones and enzymes required for vitellogenesis. In males, levels of 29 proteins changed significantly with feeding (p<0.05, FDR<0.20), including chaperones as well as motor proteins. Only two proteins, both chaperones, exhibited a significant change in both females and males with feeding. Proteins with differential accumulation patterns in females exhibited higher fold changes with feeding than did those in males. This difference may be due to major and rapid physiological changes occurring in females upon finding a host tree during the physiological shift from dispersal to reproduction. The significant accumulation of chaperone proteins, a cytochrome P450, and a glutathione S-transferase, indicate secondary metabolite-induced stress physiology related to chemical detoxification during early host colonization. The females'' activation of vitellogenin only after encountering a host indicates deliberate partitioning of resources and a balancing of the needs of dispersal and reproduction.     

Characterization of Salix nigra floral insect community and activity of three native Andrena bees

Salix nigra (black willow) is a widespread tree that hosts many species of polylectic hymenopterans and oligolectic bees of the genus Andrena. The early flowering of S. nigra makes it an important nutritive resource for arthropods emerging from hibernation. However, since S. nigra is dioecious, not all insect visits will lead to successful pollination. Using both visual observation and pan‐trapping, we characterized the community of arthropods that visited S. nigra flowers and assessed differences among male and female trees as well as the chemical and visual drivers that influenced community composition across 3 years. We found that male trees consistently supported higher diversity of insects than female trees and only three insect species, all Andrena spp., consistently visited both sexes. Additionally, Andrena nigrae, which was the only insect that occurred more on female than male flowers, correlated strongly to volatile cues. This suggests that cross‐pollinators cue into specific aspects of floral scent, but diversity of floral visitors is driven strongly by visual cues of yellow male pollen. Through time, the floral activity of two Andrena species remained stable, but A. nigrae visited less in 2017 when flowers bloomed earlier than other years. When native bee emergence does not synchronize with bloom, activity appears to be diminished which could threaten species that subsist on a single host. Despite the community diversity of S. nigra flowers, its productivity depends on a small fraction of species that are not threatened by competition, but rather rapidly changing conditions that lead to host‐insect asynchrony.     

Genomics Assisted Ancestry Deconvolution in Grape

The genus Vitis (the grapevine) is a group of highly diverse, diploid woody perennial vines consisting of approximately 60 species from across the northern hemisphere. It is the world’s most valuable horticultural crop with ~8 million hectares planted, most of which is processed into wine. To gain insights into the use of wild Vitis species during the past century of interspecific grape breeding and to provide a foundation for marker-assisted breeding programmes, we present a principal components analysis (PCA) based ancestry estimation method to calculate admixture proportions of hybrid grapes in the United States Department of Agriculture grape germplasm collection using genome-wide polymorphism data. We find that grape breeders have backcrossed to both the domesticated V. vinifera and wild Vitis species and that reasonably accurate genome-wide ancestry estimation can be performed on interspecific Vitis hybrids using a panel of fewer than 50 ancestry informative markers (AIMs). We compare measures of ancestry informativeness used in selecting SNP panels for two-way admixture estimation, and verify the accuracy of our method on simulated populations of admixed offspring. Our method of ancestry deconvolution provides a first step towards selection at the seed or seedling stage for desirable admixture profiles, which will facilitate marker-assisted breeding that aims to introgress traits from wild Vitis species while retaining the desirable characteristics of elite V. vinifera cultivars.     

Association of the invasive Haemaphysalis longicornis tick with vertebrate hosts,other native tick vectors,and tick-borne pathogens in New York City,USA

Haemaphysalis longicornis, the Asian longhorned tick, is an invasive ixodid tick that has rapidly spread across the northeastern and southeastern regions of the United States since first reported in 2017. The emergence of H. longicornis presents a potential threat for livestock, wildlife, and human health as the host associations and vector potential of this invasive pest in the United States are poorly understood. Previous field data from the United States has shown that H. longicornis was not associated with natural populations of small mammals or birds, but they show a preference for medium sized mammals in laboratory experiments. Therefore, medium and large sized mammals were sampled on Staten Island, New York, United States, to determine H. longicornis host associations and vector potential for a range of human and veterinary pathogens. A total of 97 hosts were sampled and five species of tick (Amblyomma americanum, Dermacentor variabilis, H. longicornis, Ixodes scapularis, Ixodes cookei) were found feeding concurrently on these hosts. Haemaphysalis longicornis was found in the highest proportions compared with other native tick species on raccoons (55.4%), Virginia opossums (28.9%), and white-tailed deer (11.5%). Tissue, blood, and engorged larvae were tested for 17 different pathogens using a nanoscale PCR platform. Infection with five pathogens (Borrelia burgdorferi, Anaplasma phagocytophilum, Rickettsia spp., Mycoplasma haemocanis, and Bartonella spp.) was detected in host samples, but no pathogens were found in any larval samples. These results suggest that although large and medium sized mammals feed large numbers of H. longicornis ticks in the environment, there is presently a low potential for H. longicornis to acquire pathogens from these wildlife hosts.     

EPIPHYTE FLORA AND DIVERSITY ON BASAL TRUNKS OF SIX OLD-GROWTH FOREST TREE SPECIES IN SOUTHERN AND MIDDLE BOREAL FINLAND

Epiphytic lichen and bryophyte species composition, richness and diversity were surveyed on basal trunks of six common old-growth forest tree species,Picea abies,Pinus sylvestris,Betula pendula,Alnus incana,Salix capreaandPopulus tremula, in two old-growth forest areas, one in southern and one in middle boreal Finland. The average species numbers per tree ranged from 18 (Picea) to 27 (Salix) in the southern and from 20 (Populus) to 31 (Salix) in the middle boreal area. A few widespread habitat-generalist species, such as the foliose lichensHypogymnia physodesandPlatismatia glauca, were most abundant on all the tree species, exceptPopulus. Most other epiphyte species showed at least a slight preference for one or two tree species.Populusproved to have the most distinct flora characterized by the abundance of certain, rather specialized crustose lichens and bryophytes. The number of species that occurred on only one tree species was highest onPopulus(9) in the southern and onAlnus(18) in the middle boreal area. Differences in bark acidity and structure were the most likely explanations for the differences between tree species in the epiphytic flora and diversity.SalixandPopuluswere the most important of the tree species studied for the conservation of epiphyte diversity in the boreal forests of Finland.     

Ovipositional behaviour and larval performance of Trichoferus campestris (Faldermann) (Coleoptera: Cerambycidae) on cut branches of four North American tree species

1. Velvet longhorned beetle Trichoferus campestris (Faldermann) (Coleoptera: Cerambycidae) is native to Asia. It is reported to be polyphagous in its native range, but hosts have not been screened in its introduced range in the United States.
2. We conducted choice and no-choice host experiments. For choice assays, gravid T. campestris oviposited freely on cut branches of four tree species: Juglans nigra, Malus domestica, Acer saccharum, and Pinus strobus. We investigated oviposition between apple branches with and without cankers. Half of the choice trials underwent winter temperatures.
3. For no-choice assays, eggs were placed on cut branches of these same four species. Half of these branches were later dissected to measure larval development. The rest were exposed to winter temperatures and T. campestris emergence was quantified.
4. Overall, Trichoferus campestris oviposition and development occur more readily on J. nigra and M. domestica than on A. saccharum or P. strobus. The insect oviposited more on cankered than uncankered apple wood. Cold exposure during an overwintering period benefitted insect development in adults.
5. The insect's high degree of polyphagy and ability to reproduce in dry wood has likely facilitated its establishment in multiple locales around the world.

     

Melampsora rust species on biomass willows in central and north-eastern Germany

Melampsora willow rusts are the most important fungal pathogens in short rotation coppices of biomass willows. In the past, breeding programmes for rust resistant biomass willows concentrated on the distinction of races within the forma specialis Melampsora larici-epitea f. sp. larici-epitea typica that colonized Salix viminalis and related clones. In a new breeding program that is based on a wider range of willow species it is necessary to identify further Melampsora species and formae specialis that are pathogens of willow species other than S. viminalis. Therefore, three stock collections with Salix daphnoides, Salix purpurea, and other shrub willow species (including S. viminalis) species were sampled in north-eastern Germany. A fourth stock collection in central Germany contributed rusts of tree willows (Salix fragilis and Salix alba) and the large shrub Salix caprea. Out of 156 rust samples, 149 were successfully sequenced for ITS rDNA. A phylogenetic analysis combining Neighbour-Joining, Maximum-Likelihood and Bayesian analysis revealed six species: Melampsora ribesii-purpureae, Melampsora allii-salicis-albae, Melampsora sp. aff. allii-fragilis, Melampsora larici-pentandrae, Melampsora larici-caprearum, and Melampsora larici-epitea. The first four species were found exclusively on the expected hosts. Melampsora larici-caprearum had a wider host range comprising S. caprea and S. viminalis hybrids. Melampsora larici-epitea can be further differentiated into two formae speciales. The forma specialis larici-epitea typica (59 samples) colonized Salix viminalis clones, Salix purpurea, Salix×dasyclados, and Salix×aquatica. In contrast to this relatively broad host range, f. sp. larici-daphnoides (65 samples) was found exclusively on Salix daphnoides. With the distinction and identification of the rust species/formae speciales it is now possible to test for race-specific resistances in a more targeted manner within the determined pairings of rust and willow species.     

Characterisation of seven <Emphasis Type="Italic">Inocybe</Emphasis> ectomycorrhizal morphotypes from a semiarid woody steppe

Ectomycorrhizas (ECM) of Inocybe species (Inocybaceae, Basidiomycota) formed by three host plant species (Populus alba, Salix rosmarinifolia and Pinus nigra) in a semiarid woody steppe of Hungary were studied. To identify the fungal partners, we performed phylogenetic analyses of nucleotide sequences for the internal transcribed spacer region of nuclear DNA (nrDNA ITS) together with sequences gained from public databases. Seven Inocybe ectomycorrhiza morphotypes were morpho-anatomically characterised. Five morphotypes were identified (I. phaeoleuca, I. psammophila, I. semifulva, I. splendens and I. subporospora), whereas two morphotypes represented unidentified Inocybe species. Differences were discernible among the morphotypes, and they showed general anatomical characteristics of Inocybe ECM, such as the slightly organised plectenchymatic mantle (types A, B and E and the gelatinous C). The ECM of I. subporospora and I. phaeoleuca were detected from the introduced Pinus nigra. These two fungi are probably native to the area but capable of forming a novel ectomycorrhizal association with the invasive host.     

The effects of host race, gender, and host plant distribution on alighting behavior, mating, and oviposition in Eurosta solidaginis

Eurosta solidaginis Fitch (Diptera: Tephritidae) has formed host races on Solidago altissima L. and Solidago gigantea Ait. (Asteraceae), and reproductive isolation between these host races is brought about in part by host‐associated assortative mating. Any non‐assortative mating creates the potential for gene flow between the populations, and we investigated the conditions that favored non‐assortative mating. We hypothesized that the frequency of non‐assortative mating would be influenced by differences in the behaviors of the host races and sexes and by the presence and pattern of distribution of the two host species. To test these hypotheses, we caged flies on four combinations of 32 potted host plants: all S. altissima, all S. gigantea, and cages with both host species arranged in either two pure species blocks or randomly dispersed. We recorded the number of flies of each host race that alighted on each host species and the frequency of mating within and between the host races. Males of both host races were observed on plants more frequently than females. Flies of the host race from S. gigantea (gig flies) were observed on plants in greater absolute numbers, and they mated more frequently than flies of the host race from S. altissima (alt flies). In all treatments, gig flies of both sexes were found on non‐natal host plants significantly more frequently than alt flies, and gig females showed a weaker preference for their host species than did gig males or alt flies of either gender for their respective natal hosts. Assortative mating predominated in all treatments, and flies from each host race mated more frequently in cages containing their own host plant. The frequency of non‐assortative mating varied among treatments, with the matings between alt ♀ × gig ♂ being more common in the pure S. altissima treatment and the gig ♀ × alt ♂ being more frequent in the pure S. gigantea and random treatments. Matings between gig ♂ × alt ♀ were more common overall than the reciprocal mating, because gig males were more active in pursuing matings and in alighting on the non‐natal host plant than alt flies. Non‐assortative matings were more frequent in the random than in the block treatments, but this difference was not significant. Because of strong selection against oviposition into the alternate host, we hypothesized that host plant distribution would not affect oviposition preference. We tested this hypothesis by examining the oviposition behavior of naïve, mated females in two treatments in which both host species were present: either arranged in blocks or randomly dispersed. Females oviposited only into their natal host, regardless of host plant distribution.     

Breeding Strategies in Females of the Parasitoid Wasp Spalangia endius: Effects of Mating Status and Size

Does the mating status or body size of a female parasitoid wasp affect her host size choice or propensity to burrow? In Spalangia endius, using smaller hosts appears to reduce a female's cost of parasitization but not her son's fitness. However, virgin females, which produce only sons, did not preferentially parasitize smaller hosts. Mated females also showed no host size preference. Mated females burrowed more than virgins in the presence of hosts, although not in their absence. Burrowing may reduce a mated female's harassment from males, and not burrowing may increase a virgin female's chance of mating because males avoid burrowing. Mating did not increase female longevity. Greater female size increased the offspring production of mated females burrowing for hosts but not in the absence of burrowing and not in virgin females. A female's size had no significant effect on whether her first drill attempt was on a large or a small host or on the duration of her successful drills.     

Growth and development of a generalist insect herbivore, Operophtera brumata, on original and alternative host plants

A generalist feeding strategy is common among eruptive insect herbivores but the ultimate reasons for a generalist strategy are not clear. Although generalist insect herbivores are able to complete their life cycle on several species of host plants, there is wide variation in the performance of individuals grown on different hosts. We examined whether different populations of Operophtera brumata are adapted to use the host species which is locally most abundant, and how the host plant affects growth and development of the insect. We reared two allopatric populations (eastern Finland, Prunus padus; south-west Finland, Quercus robur) on four species of host plants (Pr. padus, Populus tremula, Q. robur, Salix phylicifolia) from neonate larvae to the adult stage and measured the growth and development of individuals and the timing of adult hatching. The performance of both populations was best on Pr. padus, and the south-western population, originally on Q. robur, was well adapted to this host. The host affected the growth of females more than that of males. The host plant had an unexpected effect on hatching times of the adults. Individuals grown on the original host hatched in normal synchrony, i.e. males 6–7 days before females; but on alternative hosts this synchrony was disturbed. As is common in eruptive, capital-breeding generalist moths where female fecundity is linked to weight, host quality is critical for the flightless females of O. brumata. We suggest that in a heterogeneous environment the disturbing effect of alternative host plants on adult emergence may decrease the population density and growth rate compared to the potential maximum in a homogeneous environment. Received: 8 July 1999 / Accepted: 29 October 1999     

Body size and fitness relation in male and female Diaeretiella rapae

A strong relationship exists between body size and fitness in parasitoids. However, it is unclear whether the relationship is symmetric or asymmetric in males and females. The present study investigated the body size and fitness relationship in Diaeretiella rapae emerged from small and large nymphs of cabbage aphid Brevicoryne brassicae. A positive relationship existed between the size of the aphid host and growth of parasitoid larva developing in it. The fitness gain in males and females was not proportionate to their body size gain. Females mated with larger males produced 10?% more female offspring than females mated with smaller males. However, females that developed in large hosts produced 62?% more offspring (total male and female) than the females emerged from smaller hosts. The findings suggest that the number of offspring and the progeny sex ratio were affected by the body size of both male and female D. rapae.