Hidden Wolbachia diversity in field populations of the European cherry fruit fly, Rhagoletis cerasi (Diptera, Tephritidae)

The European cherry fruit fly Rhagoletis cerasi has been a field model for cytoplasmic incompatibility since the mid 1970s. Two Wolbachia strains were detected in this tephritid species and w Cer2 was described as the CI inducing agent dividing European populations into two unidirectional incompatible groups, i.e. southern females produce viable offspring with northern males, whereas the reciprocal cross results in incompatibility. We detected three new Wolbachia strains by sequencing a multitude of plasmids derived from Wolbachia surface protein gene ( wsp ) polymerase chain reaction (PCR) products. Strain-specific primers were developed allowing individual diagnosis without need for cloning. Hybridization of specific PCR products with a wsp oligonucleotide enhanced the detection limit significantly and revealed the presence of low-titre infections in some strains, in different ontogenetic stages and in adults of different age. We then performed a survey of strain prevalence and infection frequency in eight European regions. w Cer1 was fixed in all populations, whereas w Cer2 was detected only in the South. w Cer3 frequency was the lowest without a clear distribution pattern. The abundance of w Cer4 was homogenous across Europe. Like w Cer2, w Cer5 showed significant differences in spatial distribution. Our new findings of previously undetected and recombinant Wolbachia strains in R. cerasi reveal a major caveat to the research community not to overlook hidden Wolbachia diversity in field populations. Low-titres and geographical variability in Wolbachia diversity are expected to influence the outcome of Wolbachia population dynamics and Wolbachia- based insect population control and may create invasion barriers for expanding and artificially introduced Wolbachia strains.     

Stress magnitude matters: different intensities of pulsed water stress produce non‐monotonic resistance responses of host plants to insect herbivores

Abstract 1. Water stress may increase or reduce the suitability of plants for herbivores. The recently proposed ‘pulsed stress hypothesis’ suggests consideration of stress phenology (pulsed vs. continuous stress) to explain these conflicting effects of plant water stress on herbivore performance. 2. This hypothesis was tested for the effect of differing stress intensity on performance and preference of insect herbivores belonging to different feeding guilds, namely leaf‐chewing insects (Spodoptera littoralis caterpillars) and phloem‐feeding insects (Aphis pomi aphids), on apple plants (Malus domestica). The plants were non‐stressed or exposed to a low or high intensity of pulsed water stress. 3. Plant responses to the different stress levels were generally monotonic. Growth, stomatal conductance (g_s), leaf water, and old‐leaf nitrogen concentration decreased, whereas young‐leaf nitrogen concentration and leaf mass per area (LMA) increased with increasing stress intensity. The stable isotope composition of foliar carbon (δ¹³C) responded non‐monotonically to the drought treatments. The δ¹³C values were highest in low‐stress plants, intermediate in high‐stress plants, and lowest in non‐stressed plants. 4. The preference and performance responses of the caterpillars were also non‐monotonic. Non‐stressed plants were intermediately, low‐stress plants least, and high‐stress plants most attractive or suitable. Aphid population growth was highest on non‐stressed plants and lowest on low‐stress plants. 5. The results highlight the importance of water stress intensity for the outcome of interactions between herbivores and drought‐affected plants. They show that pulsed water stress may enhance or reduce insect herbivore performance and plant resistance, depending on stress intensity.     

Seasonal variation in larval host plants and consequences for Heliconius erato (Lepidoptera: Nymphalidae) adult body size

Abstract Adult body size, a key life history component, varies strongly within and between Heliconius erato phyllis (Lepidoptera: Nymphalidae) populations. In the present study, we determined whether seasonal variation in adult body size is temperature related and/or determined by seasonal changes of host plants (Passifloraceae) used by the larval stage. A population of H. erato phyllis located in a Eucalyptus plantation (Barba Negra Forest, Barra do Ribeiro County, Rio Grande do Sul State, Brazil) was sampled every 45 days from March 1997 to October 1998 to quantify seasonal variation in adult body size and use of larval host plants. In the laboratory, the effects of the following factors on adult body size were quantified: (i) host plant species (Passiflora misera or Passiflora suberosa); (ii) food quantity consumed by larvae (experimentally manipulated for each passion vine species); (iii) winter and summer temperatures (15 and 25°C, respectively); and (iv) the interaction between host plant species and temperature. Adults emerging during summer were larger than those emerging in other seasons. Female butterflies oviposited selectively on P. misera even when the dominant passion vine was P. suberosa. They only switched from using P. misera to P. suberosa during later autumn and winter, when P. misera vines were completely defoliated. The laboratory feeding trials with both passion vines showed a strong positive association between food quantity consumed by larvae and adult size. They also confirmed that adults are larger when their larvae are reared on P. misera than on P. suberosa. Temperature during larval development had no effect on H. erato phyllis adult size. Thus, seasonal variation of H. erato phyllis adult size in a given place is primarily determined by the availability and quality of host plant species used by the larval stage.     

Mycorrhiza modulates aboveground tri‐trophic interactions to the fitness benefit of its host plant

1. Arbuscular mycorrhiza (AM), the association of AM fungi and plant roots, may alter morphological and physiological attributes of aboveground plant parts and thereby influence plant‐associated organisms such as herbivores and their natural enemies, predators and parasitoids. 2. The interactions between AM and the players of aboveground tri‐trophic systems have mainly been considered in isolation from each other. The effects of AM on aboveground herbivore–carnivore population dynamics and the consequences to plant fitness are unknown. 3. We explored AM‐induced compensatory mechanisms for AM‐promoted proliferation of the herbivorous spider mite, Tetranychus urticae Koch, on whole bean plants, Phaseolus vulgaris L. Vegetative and reproductive plant growth, AM fungal colonisation levels, and mite densities were assessed on spider mite‐infested plants colonised or not by the AM fungus Glomus mosseae Nicol. & Gerd, and harbouring the natural enemy of the spider mites, the predatory mite Phytoseiulus persimilis Anthias‐Henriot or not. 4. AM symbiosis modulated the aboveground tri‐trophic system to the fitness benefit of the plant. AM‐increased plant productivity outweighed the fitness decrease due to AM‐promoted herbivory: at similar vegetative growth, mycorrhizal plants produced more seeds than non‐mycorrhizal plants. 5. AM‐increased spider mite population levels were compensated for by enhanced population growth of the predators and increased plant tolerance to herbivory. 6. AM‐enhanced predator performance looped back to the AM fungus and stabilised its root colonisation levels, providing the first experimental evidence of a mutually beneficial interaction between AM and an aboveground third trophic level natural enemy.     

Revised classification and evolution of leucotrichiine microcaddisflies (Trichoptera: Hydroptilidae) based on morphological and molecular data

Hydroptilidae constitute the most diverse caddisfly family, with over 2000 species known from every habitable continent. Leucotrichiinae are exclusively New World microcaddisflies, currently including over 200 species and 17 genera. Phylogenetic analyses of Leucotrichiinae relationships based on 114 morphological characters and 2451 molecular characters from DNA sequences were conducted. DNA sequences analysed were from one mitochondrial gene, cytochrome oxidase I (653 bp), and four nuclear genes, carbamoylphosphate synthase (802 bp), elongation factor 1α (352 bp), histone 3 (308 bp) and 28S rDNA (336 bp). The morphological matrix included 94 taxa (with representatives of all included genera) and the molecular matrix included 62 taxa. Individual and combined datasets were analysed under parsimony and Bayesian inference. In addition, a relaxed molecular clock divergence time estimate was conducted to determine the age of the subfamily and major lineages. All Bayesian inference analyses strongly suggest a monophyletic Leucotrichiinae, which initially diverged at approximately 124 Ma into two monophyletic groups of genera. These groups are herein elevated to tribal status, Alisotrichiini trib.n. and Leucotrichiini Flint sensu n. Several genera of Leucotrichiini were not recovered as monophyletic clades and some nomenclatural changes are proposed to reflect their phylogenetic history. These include the synonymy of Abtrichia with Peltopsyche; transfer of Betrichia hamulifera to Costatrichia; transfer of Betrichia alibrachia and Costatrichia falsa to Leucotrichia; and transfer of Costatrichia fluminensis to Acostatrichia. Additionally, Tupiniquintrichia gen.n. is described to include Peltopsyche maclachlani and Leucotrichia procera. According to our results, crown diversifications of both Alisotrichiini trib.n. (～80 Ma) and Leucotrichiini sensu n. (～103 Ma) occurred after complete separation of South America from Africa. Current distributions of most leucotrichiine genera are probably a result of migration from South America towards the north using the proto‐Caribbean archipelago (100 to 49 Ma). This published work has been registered in ZooBank, http://zoobank.org/urn:lsid:zoobank.org:pub:FB6A3385-323D-41AF-B4BE-E19A393A493C .     

Arbuscular mycorrhiza enhances preference of ovipositing predatory mites for direct prey‐related cues

Most terrestrial plants are associated with arbuscular mycorrhizal fungi but research on the effects of arbuscular mycorrhizal symbiosis on aboveground plant‐associated organisms is scarcely expanded to tri‐trophic systems. The arbuscular mycorrhizal fungus Glomus mosseae Nicol. & Gerd. enhances fitness of the two‐spotted spider mite Tetranychus urticae Koch and its natural enemy, the predatory mite Phytoseiulus persimilis Athias‐Henriot, via changes in host plant and prey quality, respectively. In the present study, it is hypothesized that gravid P. persimilis are able to recognize arbuscular mycorrhiza‐enhanced prey quality and behave accordingly. In two experiments, on leaf arenas and in cages, P. persimilis is given a choice between prey patches deriving from mycorrhizal and non‐mycorrhizal bean plants (Phaseolus vulgaris L.) as feeding and oviposition sites. The use of cages allows the manipulation of distinct patch components acting as possible cues to guide predator foraging and oviposition behaviours, such as eggs produced and traces (webbing and faeces) left by the spider mite females. Both experiments show that P. persimilis preferentially resides close to prey fed on mycorrhizal plants. The cage experiment reveals that P. persimilis uses direct prey‐related cues, mainly derived from eggs, to discern prey quality and preferentially oviposits close to prey from mycorrhizal plants. This is the first study to document that predators recognize arbuscular mycorrhiza‐induced changes in herbivorous prey quality via direct prey‐related cues.