Prerelease efficacy test of the psyllid,Arytinnis hakani,a prospective biological control agent of the invasive weed Genista monspessulana

In weed biological control, conducting a prerelease efficacy test can help ascertain if prospective biological control agents will be capable of controlling the target plant. Currently, the phloem-feeding psyllid, Arytinnis hakani, is being evaluated as a prospective agent for the exotic invasive weed, Genista monspessulana, in the USA. Small potted plants were exposed to 0, 4, 8, 12 or 16 A. hakani second-instar nymphs which were allowed to develop on the plants for six weeks in an incubator at 18°C. Increasing A. hakani densities had a significant negative impact on the number of leaflets grown, per cent change in plant height and the final number of leaflets per centimeter of plant height. Increase in plant height and the number of leaflets relative to uninfested plants were reduced by 16 and 29%, respectively, at the highest infestation levels. Psyllids did not increase leaf senescence. One of the 10 plants that was exposed to 16 psyllids died, whereas none of the others died. Weekly nymphal mortality was 10–18% at the lowest density (four psyllids), but was at least 40% at the three highest densities. Although dead nymphs were replaced weekly, insect mortality may have reduced impact on the plants, especially at the higher densities. This insect is multivoltine, so prolongation of the infestation period may have a greater impact on the plant.     

Evaluation of the impacts of herbivory by lace bugs on Chinese privet (Ligustrum sinense) survival and physiology

Biological control of Chinese privet, Ligustrum sinense, is the best long-term option for control of this widespread invasive plant in the southeastern USA. A pre-release efficacy assessment was conducted by testing the effects of damage caused by a lace bug, Leptoypha hospita, on potted privet plants in the laboratory. Inoculating 15 pairs of lace bug adults on plants resulted in a significantly higher defoliation rate and reduced leaf biomass by more than 59% compared to 0 and 3 lace bug pairs. Leaf biomass of plants inoculated with 3 and 9 pairs of lace bug did not differ significantly from control plants. The percentage of the total leaf area affected by lace bug feeding was positively correlated with the density of lace bugs inoculated. This was also evident by the reduced chlorophyll content of leaves exposed to 9 and 15 pairs of lace bugs and their offspring. Our tests showed that one generation of feeding by the lace bug caused significant defoliation as well as reduced photosynthetic activity of remaining leaves. Continuous long term feeding by the lace bug or other potential defoliating insects could result in suppression of Chinese privet populations and possibly reduction to desirable levels.     

The potential impact of the trimorphic flea-beetle, <Emphasis Type="Italic">Alagoasa extrema</Emphasis>, on a selected weedy variety of <Emphasis Type="Italic">Lantana camara</Emphasis>

The potential impact of the larval feeding by Alagoasa extrema Jacoby (Coleoptera: Chrysomelidae: Alticinae) on potted plants of its host Lantana camara L. (Verbenaceae), a weed of major importance in South Africa, was examined. Under quarantine laboratory conditions, 2-month old plants of L. camara variety 029 White Pink were exposed to different larval feeding densities for a period of 18 days (completion of the larval stage). The above-ground dry mass of plants was significantly reduced following attack by larvae at densities of 5 larvae per plant (20% reduction) and 10 larvae per plant (28% reduction), when compared to unattacked plants. Attack by larvae over this short period had no significant impact on root growth. This demonstrates that A. extrema, once established in climatically favourable areas, could well augment other established agents in defoliating L. camara stands, reducing the accumulation of reserves and the competitiveness of the weed.     

Impact of herbivory on performance of <Emphasis Type="Italic">Vincetoxicum</Emphasis> spp., invasive weeds in North America

The alien invasive vines Vincetoxicum rossicum and Vincetoxicum nigrum (swallow-wort) are of major concern in eastern North America, where both species invade forested landscapes and threaten faunal and plant diversity. Among the few native natural enemies reported in Eurasia, the specialist chrysomelid, Chrysochus (Eumolpus) asclepiadeus (Coleoptera; Chrysomelidae), feeds on Vincetoxicum both above ground (as adults) and below ground (as larvae). The goal of our study was to assess the potential for using this beetle to manage invasive Vincetoxicum spp. in North America by quantifying the impact of herbivory by C. asclepiadeus on Vincetoxicum and determining whether this effect was influenced by plant density (“Allee effect”). Experimental work was carried out using a split plot design in the field in southern France. Pots of V. nigrum and V. hirundinaria, a substitute for V. rossicum, were planted at high (255 plants/m²), medium (127 plants/m²), and low (32 plants/m²) plant densities, and received treatments of 0 (control), 2 or 4 C. asclepiadeus adult beetles/pot. Leaf damage, root and shoot biomass, and quantity of seeds were measured after 4 weeks of adult feeding. Densities of 2 and 4 beetles/pot caused similar damage, with significant reductions in plant biomass at low plant density. While V. hirundinaria increased allocation of resources to roots in response to herbivory, V. nigrum did not. Seed production was greatest for both species grown at low plant densities, but only V. nigrum produced fewer seeds in response to herbivory. Our results, based on the effects of herbivory by C. asclepiadeus adults, suggest that if this beetle were to be introduced into North America for the management of Vincetoxicum spp. such as V. rossicum, reductions in plant biomass and spread would be greatest if beetles were released on edges or in newly-established satellite populations at low plant densities. In the case of V. nigrum, beetles could be released irrespective of plant density as reproductive output and seed dispersal would be reduced similarly.     

Plant–animal interactions between carnivorous plants,sheet‐web spiders,and ground‐running spiders as guild predators in a wet meadow community

1. Plant–animal interactions are diverse and widespread shaping ecology, evolution, and biodiversity of most ecological communities. Carnivorous plants are unusual in that they can be simultaneously engaged with animals in multiple mutualistic and antagonistic interactions including reversed plant–animal interactions where they are the predator. Competition with animals is a potential antagonistic plant–animal interaction unique to carnivorous plants when they and animal predators consume the same prey.
2. The goal of this field study was to test the hypothesis that under natural conditions, sundews and spiders are predators consuming the same prey thus creating an environment where interkingdom competition can occur.
3. Over 12 months, we collected data on 15 dates in the only protected Highland Rim Wet Meadow Ecosystem in Kentucky where sundews, sheet‐web spiders, and ground‐running spiders co‐exist. One each sampling day, we attempted to locate fifteen sites with: (a) both sheet‐web spiders and sundews; (b) sundews only; and (c) where neither occurred. Sticky traps were set at each of these sites to determine prey (springtails) activity–density. Ground‐running spiders were collected on sampling days. DNA extraction was performed on all spiders to determine which individuals had eaten springtails and comparing this to the density of sundews where the spiders were captured.
4. Sundews and spiders consumed springtails. Springtail activity–densities were lower, the higher the density of sundews. Both sheet‐web and ground‐running spiders were found less often where sundew densities were high. Sheet‐web size was smaller where sundew densities were high.
5. The results of this study suggest that asymmetrical exploitative competition occurs between sundews and spiders. Sundews appear to have a greater negative impact on spiders, where spiders probably have little impact on sundews. In this example of interkingdom competition where the asymmetry should be most extreme, amensalism where one competitor experiences no cost of interaction may be occurring.

     

Attractiveness of host volatiles combined with background visual cues to the tea leafhopper,Empoasca vitis

The tea green leafhopper, Empoasca vitis (Göthe) (Hemiptera: Cicadellidae), is a serious pest of tea plants. We examined the behavioral responses of E. vitis adults to odors from the shoots of three host plants in a Y‐tube olfactometer with background visual cues. The host plants were tea [Camellia sinensis (L.) Kuntze (Theaceae)], peach [Prunus persica (L.) Siebold & Zucc. (Rosaceae)], and grapevine [Vitis vinifera L. (Vitaceae)]. Volatiles from the shoots were analyzed. Both yellow‐green and gold backgrounds enhanced the olfactory responses of E. vitis adults to tea plant odors, and this enhancement was stronger under a high light intensity. On the yellow‐green background, E. vitis adults significantly preferred the odors from shoots of the three host plants compared with clean air. Moreover, E. vitis adults preferred grapevine odor over the tea plant odor. The volatile blends of the three plant species were distinctly different. Peach plant shoots emitted the greatest amount of volatiles, whereas grapevine shoots released the greatest diversity of compounds. These results provide evidence that background visual cues could enhance the response of E. vitis adults to host‐plant volatiles. The leafhoppers can discern different host odors, suggesting the possibility of using peach plant and grapevine odors to monitor and manage this pest in tea plantations.     

Interactive effects of mycorrhizal fungi,salt stress,and competition on the herbivores of Baccharis halimifolia

1. Plant stress and association with mycorrhizal fungi have been shown to significantly influence plant quality, yet their roles in influencing plant–insect interactions remain unclear. Even less is known about how these factors might interact with or be modified by within‐trophic level interactions. 2. In the present study, the results of a factorial field experiment are reported in which the effects of within‐trophic‐level interactions, plant stress, and mycorrhizae on three herbivores of Baccharis halimifolia were examined. 3. Plant stress was increased by adding salt to the soil, and availability of mycorrhizal fungi was increased by inoculating plant roots. These treatments were applied to plants with either low or high densities of a competitor (Trirhabda baccharidis). 4. For the two leaf miners, Amauromyza maculosa and Liriomyza trifolii, increased soil salinity and high densities of the competitor Trirhabdabaccharidis resulted in significant decreases in density. Neither of these treatments affected the gall maker Neolasioptera lathami. 5. Mycorrhizal fungi increased the densities of all three herbivores, possibly by increasing foliar nitrogen levels. For the two leaf miners, there was also evidence that mycorrhizae ameliorated the negative effects of salt stress. There was also evidence that high levels of competition dampened the positive effects of mycorrhizae on the two leaf miners.     

Field and tree distribution of Capnodis tenebrionis (Linnaeus, 1767) (Col., Buprestidae) adults in an apricot orchard in Italy

A study was conducted into the spatio–temporal distribution of adult Capnodis tenebrionis (Linnaeus, 1767) in an apricot orchard in Sicily (Italy) using inverse distance squared weighting (IDW), a spatial interpolation technique to create a distribution map of adults in the orchard. The study was conducted throughout the period of presence of the adult in the field and it investigated distribution on individual plants with regard to the observed height on the crown and exposure to the sun’s rays. The variation is gradual in the distribution of the buprestid in the field and the areas with the greatest exposition to the sun (south‐east) were marked by the highest densities. The presence of the pest was also found to be higher in those parts of the crown most exposed to the sun; moreover, the position in relation to the ground varied constantly and was increasingly linked to time and temperature. The data obtained confirmed the distinct thermal demands of the species and provided useful information on both sampling and control.     

The differential impact of a native and a non‐native ragwort species (Senecioneae) on the first and second trophic level of the rhizosphere food web

Whereas the impact of exotic plant species on above‐ground biota is relatively well‐documented, far less is known about the effects of non‐indigenous plants on the first and second trophic level of the rhizosphere food web. Here, rhizosphere communities of the invasive narrow‐leaved ragwort Senecio inaequidens and the native tansy ragwort Jacobaea vulgaris, co‐occurring in three semi‐natural habitats are compared. For both species, two life stages were taken into consideration. Quantitative PCR assays for the analyses of bacterial and fungal communities at a high taxonomic level were optimized, and it was investigated whether changes in the primary decomposer community were translated in alterations in bacterivorous and fungivorous nematode communities. In contrast to J. vulgaris, small but significant reductions were observed for Actinobacteria and Bacteroidetes (both p < 0.05) in case of the invasive S. inaequidens. More pronounced changes were detected for the overall nematode community density, and, more specifically, for the bacterivorous genus Anaplectus and the family Monhysteridae (both p < 0.05), as well as the necromenic Pristionchus (p < 0.001). At high taxonomic level, no differences were observed in fungal rhizosphere communities between native and non‐native ragwort species. The impact of plant developmental stages on rhizosphere biota was prominent. The overall bacterial and fungal biomasses, as well as a remarkably consistent set of constituents (Actinobacteria, α‐ and β‐Proteobacteria and Bacteroidetes) were negatively affected by plant stage for both ragwort species. Although later developmental stages of plants generally coincided with lower levels for individual nematode taxa, densities of the fungivorous genera Diphtherophora and Tylolaimophorus remain unaltered. Hence, even at a high taxonomic level, differential effects of native and non‐native ragwort could be pinpointed. However, plant developmental stage has a more prominent impact and this impact was similar in nature for both native and non‐native ragwort species.     

Effects of a nematode Meloidogyne incognita and its interaction with above‐ground herbivory on an invasive wetland plant,alligator weed (Alternanthera philoxeroides)

Invasive plants may be attacked both above ground and below ground. Few studies have, however, investigated the simultaneous effects of above‐ground and below‐ground herbivory. In the present study, we report the effects of beetle herbivory and nematode infection on alligator weed, Alternanthera philoxeroides, an invasive plant in China. We found that the root‐knot nematode Meloidogyne incognita widely occurred on the plant in south China. To examine its effect on the plant in conjunction with above‐ground herbivory, we conducted a field common garden experiment with a local insect defoliator, Cassida piperata. We also included the native congener Alternanthera sessilis in our experiments for a comparison of the response of invasive and native species. We found no significant effects on plant biomass of the nematode infection in conjunction with the above‐ground herbivory. Further chemical analysis, however, showed that the water‐soluble carbohydrate content in roots of A. philoxeroides was significantly increased in plants attacked by both the nematode and the herbivore compared with the water‐soluble carbohydrate content in plants attacked by only the nematode or herbivore alone. We found no such change in the native congener A. sessilis. Together these results may suggest that A. philoxeroides tolerates joint above‐ground and below‐ground damage by allocating more resources to below‐ground material.     

Initiation of fungal epizootics in diamondback moth populations within a large field cage: proof of concept for auto-dissemination

Adult diamondback moths (DBM), Plutella xylostella L. (Lepidoptera: Plutellidae), inoculated with the fungus Zoophthora radicans, were released within a large field cage containing DBM‐infested potted broccoli plants. Larvae and pupae on exposed and caged control plants were examined on five occasions over the next 48 days for evidence of Z. radicans infection. Infected larvae were first detected on exposed plants 4 days after the initial release of adults, and after 48 days the infection level reached 79%. Aerially borne conidia were a factor in transmission of the fungus. Infection had no effect on possible losses of larval and adult cadavers due to scavengers in field crops. In a trial to measure the influence of infection on dispersal, twice as many non‐infected as infected males were recaptured in pheromone traps, although the difference in cumulative catch only became significant 3 days after release of the males. In a separate experiment, when adult moths were inoculated with Beauveria bassiana conidia and released into the field cage, DBM larvae collected from 37 of 96 plants sampled 4 days later subsequently died from B. bassiana infection. The distribution of plants from which the infected larvae were collected was random, but the distribution of infected larvae was clustered within the cage. These findings suggest that the auto‐dissemination of fungal pathogens may be a feasible strategy for DBM control, provided that epizootics can be established and maintained when DBM population densities are low.     

Laboratory and greenhouse evaluation of a synthetic host volatile attractant for Colorado potato beetle, Leptinotarsa decemlineata (Say)

Abstract 1 The attractiveness of potato plants treated with a synthetic host volatile blend [(Z)‐3‐hexenyl acetate (+/–)‐linalool, and methyl salicylate] to newly emerged and 5‐day‐old adult Colorado potato beetle, Leptinotarsa decemlineata (Say), was compared at four doses against untreated control plants and plants treated with an azadirachtin‐based antifeedant in greenhouse cage arenas. 2 Attractant‐treated plants (derived release rates of 0, 5.7, 17.1 or 57 µg/h) were significantly more attractive than untreated control plants to newly emerged and 5‐day‐old adults only at 57 µg/h. 3 Attractant‐treated plants were significantly more attractive than antifeedant‐treated plants to newly emerged and 5‐day‐old adults at the 5.7 µg/h treatment level and higher. Mean insect density on attractant‐treated plants in the attractant/antifeedant study was significantly higher than in the attractant/control study. 4 Habituation to the synthetic attractant was evaluated by exposing adult beetles to the synthetic attractant for 0, 1, 2.5, 4, 8, 12 or 16 h, before release into a wind tunnel in which an attractant‐baited plant model was placed at the upwind end. Insects exposed to the synthetic host attractant for ≤ 8 h moved to the synthetic attractant‐baited plant model whereas insects exposed to the synthetic host attractant for 12 and 16 h did not. Furthermore, beetles exposed to the synthetic attractant for 0 and 1 h moved at rates greater than, or equal to, the median whereas beetles exposed for longer time periods moved at rates significantly less than the median. 5 These results demonstrate the potential for using the synthetic plant attractant and an antifeedant as components in a stimulo‐deterrent strategy for management of the Colorado potato beetle as shown by us in another study.     

Root herbivory induces an above-ground indirect defence

Indirect plant defences have largely been studied within the scope of above‐ground interactions. Here we provide novel evidence that root herbivory can induce an above‐ground indirect defence. Cotton plants (Gossypium herbaceum) exposed to root‐feeding wireworms (Agriotes lineatus) increased their foliar extrafloral nectar production ten‐fold in comparison to undamaged control plants. Mechanical root damage also yielded an increase in nectar production. In nature, extrafloral nectar production allows plants to recruit predators, which in turn protect the plant against above‐ground insect herbivores. Our results show that root‐feeding herbivores may alter such above‐ground defensive interactions.     

The effects of trophic structure and soil fertility on the assembly of plant communities: a microcosm experiment

Using closed, ventilated outdoor microcosms, plant communities were allowed to assemble from a pool of 48 herbaceous species comprising a wide range of plant functional types. The experiment involved factorial manipulation of soil fertility, invertebrate herbivores (slugs, grass aphids) and their predators (ground beetles, ladybirds). In the absence of herbivores the vegetation on soils of high, moderate and low fertility was dominated by plant species which under natural field conditions are restricted to fertile soils. At high fertility, the rate of competitive exclusion was rapid compared with communities persisting at lower fertility which remained species‐rich with high densities of individuals.
The effects of herbivory were profound and attributable mainly to the slug Deroceras reticulatum. At moderate and low soil fertility the main effect of herbivores was to change the ranking of plant species; palatable grasses (e.g. Poa annua, Poa trivialis and Lolium perenne) were suppressed and plant species of slower growth rate (e.g. Festuca rubra, Anthoxanthum odoratum, Festuca ovina) were promoted. More subtle impacts of herbivory altered the size structure of plant populations suggesting the preference, by slugs, for seedlings and small (suppressed) plants. Although ladybirds and their larvae persisted in low numbers in some microcosms, carnivory was more strongly in evidence (lower densities of D. reticulatum and reduced consumption of lettuce discs) in relation to the activities of the ground beetle Pterostichus melanarius. Only in the low fertility treatment, however, was this potential translated into effects on vegetation; for several plant species the frequency of large individuals increased in the presence of P. melanarius.
We conclude that outdoor microcosms provide a valuable ecological tool and, in particular, allow investigation of (a) the role of herbivores in promoting slow‐growing plant species in the vegetation of infertile habitats and (b) the protection of palatable plants against herbivores by carnivores.     

Consumptive and non‐consumptive effects of wolf spiders on cucumber beetles and cucumber plant damage

Biological control research often focuses on the ability of predators to reduce pest densities and protect crops through consumption. Less studied is their ability to protect crops by altering pest behaviour (non‐consumptive effects). Lab experiments were conducted to test predation rates of striped cucumber beetles (Acalymma vittatum; Coleoptera: Chrysomelidae) and spotted cucumber beetles (Diabrotica undecimpunctata howardi; Coleoptera: Chrysomelidae) by large (>10 mm) wolf spiders (Araneae: Lycosidae). Field experiments were conducted to examine how the physical presence and/or cues of spiders impact the behaviour and mortality of A. vittatum (specialist) and D. undecimpunctata (generalist) cucumber beetles as well as growth and damage of cucumber plants (Cucumis sativus; Cucurbitaceae). A. vittatum and D. undecimpunctata adults were added to caged cucumber plants without a spider, with spider cues only (spider removed before beetle inclusion), with spider only (spider introduced to plants immediately before beetle inclusion), and with spiders and their cues present (spiders introduced 24 hr in advance of beetle inclusion). A. vittatum responded to spider cues primarily by emigrating from plants. Contrarily, D. undecimpunctata did not display obvious responses, such as reduced feeding or increased emigration, to spider foraging and/or cues. Actively foraging lycosids increased A. vittatum mortality and reduced densities of D. undecimpunctata in the field when cucumber plants were flowering. This study highlights how non‐consumptive and consumptive effects can play a role in modifying pest populations, and how these effects can vary across species and plant growth stages.     

Stimulation of Armillaria mellea by phenolic fungicides

Phenolic fungicides, which were initially fungicidal to mycelium of Armillaria mellea on the surface of well‐colonised wood billets, eventually stimulated the growth of A. mellea. An extensive growth of rhizomorphs was produced from A. mellea inoculum, which had been exposed to phenolic chemicals for 3 months, compared to few or no rhizomorphs produced from inoculum exposed to water or a suspension of a non‐phenolic fungicide, fenpropidin. Inoculated privet plants grown either in pots or under field conditions were treated with a range of fungicides; fenpropidin, phenyl phenol, cresylic acid or water (control) was applied every 6 months over 21/2 yr. Fenpropidin caused a slightly (but significantly) lower incidence of infection than occurred in untreated plants, but the phenolic fungicides, cresylic acid and phenyl phenol, did not reduce the incidence of infection. The severity of infection (% root circumference colonised at 5 cm depth) was greater following cresylic acid treatments than the other fungicides or water‐treated controls. Use of phenolic fungicides such as cresylic acid for the control of A. mellea may therefore be counter‐productive.     

Relationships between food quality and fitness in the desert locust, Schistocerca gregaria, and its distribution over habitats on the Red Sea coastal plain of Sudan

The effect of millet, Pennisetum typhoideum Rich. (Poaceae), leaf nitrogen content on fitness parameters of the desert locust, Schistocerca gregaria Forsk. (Orthoptera: Acrididae), was studied under laboratory conditions. Locusts reared on high‐nitrogen leaves were larger, developed faster, had higher survival, reproduced more and earlier, and showed greater synchronization than those fed on low‐nitrogen leaves. Active and passive cannibalism contributed to mortality when locusts were reared on low‐nitrogen leaves, but not when reared on high‐nitrogen leaves. Elevated leaf nitrogen content of host plants increased net reproduction and intrinsic rate of increase, and lowered generation time. The findings show that nitrogen content of host plants affects the potential for population increase in the desert locust. Leaf samples of common plant species were collected in the Heliotropium arbainense (Fresen.) (Boraginaceae) and Panicum turgidum (Forssk.) (Poaceae) plant communities on the Red Sea coastal plain of Sudan during the winters of 1999 and 2000. The levels of leaf nitrogen in host plants were comparable to those in the laboratory studies and consistently higher in plant samples from the Heliotropium community than in samples from the Panicum community. Both in 1999 and 2000, locust densities were much higher in the Heliotropium than in the Panicum plant community. It should be assessed whether the desert locust would be attracted to sites where host plants have high leaf nitrogen content, as this would not only increase their fitness, but also the likelihood of gregarization and outbreaks.     

Settling behavior of the glassy‐winged sharpshooter,Homalodisca vitripennis,vector of Xylella fastidiosa,on southern highbush blueberry cultivars

The xylem‐limited bacterium Xylella fastidiosa Wells, Raju, Hung, Wiseberg, Mandelico‐Paul & Brenner causes bacterial leaf scorch, a new disease of southern highbush blueberry [Vaccinium corymbosum L. (Ericaceae) interspecific hybrids] in the southeastern USA. The bacterium is transmitted by sharpshooter leafhoppers (Hemiptera: Cicadellidae), with the glassy‐winged sharpshooter (GWSS), Homalodisca vitripennis (Germar), being the most common potential vector in blueberry plantings. Considerable differences are observed in disease intensity among blueberry cultivars in the field, but it remains unknown whether these differences are due to variations in cultivar susceptibility to the bacterium, differences in attractiveness to its vector(s), or both. The settling and feeding behavior of GWSS was evaluated on three southern highbush blueberry cultivars (FL 86‐19, Star, and Emerald) in the greenhouse; in previous field studies, these cultivars were found to be affected by bacterial leaf scorch at high, moderate, and low levels, respectively. Potted plants were caged together with field‐collected GWSS adults for a period of 5 days, with either all three cultivars caged simultaneously (choice test) or individually (no‐choice test). In the choice tests, no differences in cultivar attractiveness were observed during the first 2 days of study. However, from the 3rd day, significantly more adults settled on Emerald (52.7%) than on Star (25.5%) and FL 86‐19 (17.7%). In contrast, in no‐choice tests, the overall host plant acceptance for the three cultivars was similar, and 89.3–92.1% of adults settled on these plants. A significantly greater number of adults settled on the stems (79.3%) vs. the leaves (11.2%). Moreover, they preferred the middle portion of the shoot (56.9%) compared with the upper (7.8%) and the lower (14.7%) portions. In a separate study on FL 86‐19, greater numbers of GWSS nymphs settled on the upper (actively growing) portion of the shoot (82.3%), whereas only 15.8 and 1.5% settled on the middle and lower portions, respectively.     

From the laboratory to the field: contrasting effects of multi-trophic interactions and agroforestry management on coffee pest densities

Only few factors influencing pest populations can be studied in the laboratory, but many population‐driving factors interact in the field. Therefore, complementary laboratory and field approaches are required for reliable predictions of real‐world patterns and processes. Laboratory and field experiments with the red spider mite, Oligonychus ilicis McGregor (Acari: Tetranychidae), and the coffee leaf miner, Leucoptera coffeella Guérin‐Méneville (Lepidoptera: Lyonetiidae), on coffee plants, Coffea arabica L. (Rubiaceae), were combined to study the relative importance of biotic interactions, including resource preferences and natural‐enemy impact, and habitat factors, such as agroforestry type and management intensity, on coffee pest densities. In the laboratory, leaf discs cut from undamaged coffee plants were significantly preferred by red spider mites over those from plants infested with conspecific mites, leaf rust pathogens [Hemileia vastatrix Berkeley & Broome (Uredinales)], or coffee leaf miners, resulting in higher reproductive success. Similarly, undamaged plants were preferred by coffee leaf miners over red spider mite‐infested plants. However, in the field, red spider mite densities were positively correlated with coffee leaf miner and leaf rust densities, thereby contrasting with laboratory predictions. Hence, our study suggests that the importance of resource preferences and fitness expected based on laboratory experiments was suppressed by environmental conditions in the field, though other unassessed biotic interactions could also have played a role. Furthermore, intensified agroforestry was characterized by higher red spider mite densities, whereas densities of its major natural enemy, the predatory mite Amblyseius herbicolus Chant (Acari: Phytoseiidae), were not related to agroforestry management. Densities of coffee leaf miner and its main natural enemy, a eulophid parasitoid (Hymenoptera), were not affected by management practices. In conclusion, patterns found in the laboratory did not hold for the field, emphasizing the difficulties of extrapolating small‐scale experiments to larger spatial scales and the need to combine both approaches.     

Seed preferences by rodents in the agri‐environment and implications for biological weed control

Post‐dispersal seed predation and endozoochorous seed dispersal are two antagonistic processes in relation to plant recruitment, but rely on similar preconditions such as feeding behavior of seed consumers and seed traits. In agricultural landscapes, rodents are considered important seed predators, thereby potentially providing regulating ecosystem services in terms of biological weed control. However, their potential to disperse seeds endozoochorously is largely unknown. We exposed seeds of arable plant species with different seed traits (seed weight, nutrient content) and different Red List status in an experimental rye field and assessed seed removal by rodents. In a complementary laboratory experiment, consumption rates, feeding preferences, and potential endozoochory by two vole species (Microtus arvalis and Myodes glareolus) were tested. Seed consumption by rodents after 24 h was 35% in the field and 90% in the laboratory. Both vole species preferred nutrient‐rich over nutrient‐poor seeds and M. glareolus further preferred light over heavy seeds and seeds of common over those of endangered plants. Endozoochory by voles could be neglected for all tested plant species as no seeds germinated, and only few intact seeds could be retrieved from feces. Synthesis and applications. Our results suggest that voles can provide regulating services in agricultural landscapes by depleting the seed shadow of weeds, rather than facilitating plant recruitment by endozoochory. In the laboratory, endangered arable plants were less preferred by voles than noxious weeds, and thus, our results provide implications for seed choice in restoration approaches. However, other factors such as seed and predator densities need to be taken into account to reliably predict the impact of rodents on the seed fate of arable plants.