Effect of host‐cocoon mass on adult size in the secondary hyperparasitoid wasp,Pteromalus semotus (Hymenoptera: Pteromalidae)

Abstract Parasitoids have long proven to be model organisms in studying resource‐related constraints on immature development. Here we examine the relationship between host cocoon (= pupal) size in the gregarious endoparasitoid wasp, Cotesia glomerata, and development time and adult size in the solitary idiobiont hyperparasitoid, Pteromalus semotus. Little is known about the biology or ecology of this ecto‐hyperparasitoid species, although it is one of the major secondary hyperparasitoids of C. glomerata. The size of the adult wasp covaried with the size of the host cocoon at parasitism. Moreover, female wasps were larger than male wasps for a given cocoon size. Adult wasps have remarkably long life‐spans, 3 months on average. Longevity did not significantly differ with sex. We also examined how larvae of P. semotus exclude other potential competitors. P. semotus is protandrous, with females taking significantly longer to complete their development than males. In experiments where several eggs of P. semotus were placed on individual pupae of C. glomerata, newly hatched hyperparasitoid larvae moved rapidly over the surface of the host and destroyed the eggs of any conspecifics by biting them before they would initiate feeding on host tissues. Our results are discussed in relation to those with other studies with solitary ichneumonid idiobiont hyperparasitoids of C. glomerata.     

Diet and Geophagy Across a Western Amazonian Parrot Assemblage

We identified species‐ and community‐level dietary characteristics for a species‐rich Amazonian parrot assemblage to determine relationships among dietary metrics and use of geophagy sites. Previous studies suggest that soil is consumed at geophagy sites in this region mainly to supplement dietary sodium. We accumulated 1400 feeding records for 16 parrot species over 2 yr and found that seeds, flowers, and fruit pulp featured prominently in diets, while bark, insects, and lichen were consumed in small quantities. Food availability across 1819 trees was measured, and we found that flower availability was highest in the dry season and fruit production peaked in the wet season, but that phenology patterns of the 20 most commonly foraged plant species suggest no serious food bottlenecks. Partitioning of available food resources among the 13 most commonly encountered parrots is suggested by an ordination analysis (DCA), which placed the large macaws (Ara) with the Amazona parrots at the ‘primary forest’ end of a dietary resource axis and four smaller species at the ‘successional forest’ end of the axis. Parrot species associated with successional forest also consumed less plant species overall. Furthermore, these parrot species consuming successional forest resources had higher claylick visitation rates than those consuming primary forest resources suggesting they derive the greatest benefits from soil consumption.     

The edible katydid Ruspolia differens is a selective feeder on the inflorescences and leaves of grass species

Ruspolia differens (Serville) (Orthoptera: Tettigoniidae, Conocephalinae) (its common names including ‘African edible bush‐cricket’, ‘edible grasshopper’, and ‘nsenene’) is an important source of food for humans in East Africa, but its ecology and biology are poorly understood. We explored the host plants of R. differens with a series of no‐choice and multiple‐choice laboratory experiments using 18 local common grass and sedge species in Uganda. In no‐choice experiments, the degree of acceptance differed significantly among the studied plant species, but in only three species were leaves rejected and in one species were inflorescences rejected. The pattern of acceptance among plant species was different in the local vs. swarming populations. Leaves were generally more accepted by the local population, whereas inflorescences were generally more accepted by the swarming population. Both leaves and inflorescences were more readily accepted by males than by females. According to the multiple‐choice experiments, R. differens preferred inflorescences over leaves. Our results demonstrate that R. differens is a facultatively oligophagous grass‐specialist, which has a clear preference for certain grass or sedge species (especially inflorescences), but it accepts many host plants if the preferred ones are not available. To preserve viable natural populations of R. differens in East Africa in the long term, our results draw special attention to the availability of grasslands where accepted and preferred host plants are available year‐round.     

An exotic parasitoid provides an invasional lifeline for native parasitoids

The introduction of an exotic species may alter food webs within the ecosystem and significantly affect the biodiversity of indigenous species at different trophic levels. It has been postulated that recent introduction of the brown marmorated stinkbug (Halyomorpha halys (Stål)) represents an evolutionary trap for native parasitoids, as they accept H. halys egg masses as a host but produce no viable progeny. Interspecific interactions between European egg parasitoid, Trissolcus cultratus (Mayr), and an Asian parasitoid, Trissolcus japonicus (Ashmead), were assessed by providing egg masses to T. cultratus at various time intervals following the initial parasitization by T. japonicus. The suitability of the host for the parasitoid development was re‐assessed by providing T. cultratus with fresh and frozen egg masses of various ages. The likelihood of T. cultratus being able to attack previously parasitized egg masses was determined by assessing the duration of egg mass guarding behavior by T. japonicus following parasitization. The results of experiments examining the interspecific interactions between a native European egg parasitoid, T. cultratus, and an Asian parasitoid, T. japonicus (a candidate for the biological control of H. halys), showed that the native species can act as facultative hyperparasitoid of the exotic one. Although this is only possible during certain stages of T. japonicus development, the presence of the introduced parasitoid may reduce the impact of the evolutionary trap for indigenous parasitoid species. There is a possibility that the occurrence of facultative hyperparasitism between scelionid parasitoids associated with stinkbugs is common. This resulting intraguild predation could promote conservation and stabilization of natural communities by impacting the diversity and population dynamics of native stinkbugs and their parasitoids (e.g., by allowing native parasitoids to avoid wasting reproductive effort on unsuitable hosts), or reduce success of biological control programs (e.g., by reducing the population size of the exotic parasitoids).     

Woody plants' diversity,structural analysis and regeneration status of Wof Washa natural forest,North‐east Ethiopia

Wof‐Washa forest is one of the few remaining dry Afromontane forests in the central plateau of Ethiopia. Woody species composition, structure and regeneration patterns of this forest were studied to generate information essential for formulating feasible management options for the forest. Vegetation data were collected from 64 quadrats of size 20 m × 20 m, 10 m × 10 m and 5 m × 5 m for tree/shrub, sapling and seedling, respectively, laid systematically along transects. A total of 62 woody species belonging to 54 genera and 40 families were recorded. Rosaceae was the most diverse family with five (12.5%) species followed by Anacardiaceae, Euphorbiaceae and Myrsinaceae with three (7.5%) species each. Tree/shrub, sapling and seedling densities were 699, 1178 and 7618.7 individuals/ha. About 56.7% of the importance value index was contributed by Juniperus procera, Maytenus arbutifolia, Podocarpus falcatus and Ilex mitis. Vegetation classification resulted in five plant communities: Ilex mitis – Maytenus obscura, Galiniera saxifraga – Maesa lanceolata, Juniperus procera – Erica arborea, Podocapus falcatus – Allophylus abyssinicus and Pittosporum viridiflorum – Polycias fulva community types. Regeneration status of all the woody plant species was categorized as ‘Good’ (28%), ‘Fair’ (19%), ‘Poor’ (8%), ‘None’ (40%) and ‘New’ (5%).     

The effect of direct and indirect defenses in two wild brassicaceous plant species on a specialist herbivore and its gregarious endoparasitoid

Most studies on plant defenses against insect herbivores investigate direct and indirect plant defenses independently. However, these defenses are not necessarily mutually exclusive. Plant metabolites can be transmitted through the food chain and can also affect the herbivore's natural enemies. A conflict may arise when a natural enemy is attracted to a plant that is suboptimal in terms of its own fitness. In addition, plant defenses are often studied in cultivated plant species in which artificial selection may have resulted in reduced resistance against insect herbivores. In this study, we investigated both direct and indirect plant defenses in two closely related wild brassicaceous plant species, Brassica nigra L. and Sinapis arvensis L. The herbivore Pieris brassicae L. (Lepidoptera: Pieridae), which is specialized on brassicaceous plant species, developed faster and attained higher pupal mass when reared on B. nigra than on S. arvensis. In contrast, Cotesia glomerata L. (Hymenoptera: Braconidae), which is a gregarious endoparasitoid of P. brassicae caterpillars, developed equally well on P. brassicae irrespective of the food plant on which its host had been reared. The feeding strategy of the parasitoid larvae, that is, selectively feeding on hemolymph and fat body, is likely to allow for a much wider host‐size range without affecting the size or development time of the emerging parasitoids. In flight chamber experiments, C. glomerata, which had an oviposition experience in a host that fed on Brussels sprout, exhibited significant preference for host‐damaged B. nigra over host‐damaged S. arvensis plants. Headspace analysis revealed quantitative and qualitative differences in volatile emissions between the two plant species. This parasitoid species may use a range of cues associated with the host and the host's food plant in order to recognize the different plant species on which the host can feed. These results show that there is no conflict between direct and indirect plant defenses for this plant–host–parasitoid complex.     

Foraging strategies of generalist and specialist Old World nectar bats in response to temporally variable floral resources

Foraging theory predicts that generalist foragers should switch resources more readily, while specialist foragers should remain constant to preferred food resources. Plant‐pollinator interactions provide a convenient system to test such predictions because floral resources are often temporally patchy, thus requiring long‐lived pollinators to switch resources seasonally. Furthermore, flowering phenologies range from ‘steady‐state’ (low‐rewarding but highly reliable) to ‘big‐bang’ (high‐rewarding but ephemeral) plant species. We assessed how nectarivorous Old World bats respond to this temporally variable floral environment by examining their diets throughout the year. Over 15 months of fieldwork in southern Thailand, we simultaneously: (1) recorded the flowering phenologies of six bat‐pollinated plant taxa; and (2) assessed the diets of seven common flower‐visiting bat species. As predicted, the generalist nectarivore (Eonycteris spelaea) frequently switched diets and utilized both big‐bang and steady‐state resources, while the specialist nectarivores (Macroglossus minimus and M. sobrinus) foraged on one or two steady‐state plant species year‐round. Our results suggest that larger and faster bat species are able to fly longer distances in search of big‐bang resources, while smaller bat species rely on highly predictable food resources. This study supports the theory that generalist foragers have flexible diets, while specialist species restrict foraging to preferred floral resources even when other floral resources are more abundant. Moreover, these findings demonstrate how plant flowering phenology and pollinator diet breadth can shape the frequency and constancy of pollinator visits; we further discuss how such interactions can influence the potential extent of gene flow within a patchy floral environment.     

Seasonality and life cycles of woody plant-feeding noctuid moths (Lepidoptera: Noctuidae) in Mediterranean habitats

Abstract.

• 1 The annual cycle of noctuid moths feeding as larvae on the foliage of eighteen woody plant species (belonging to ten different families) was studied at two southeastern Spanish Mediterranean forest habitats. Two questions were addressed in this study. (1) Does the rigorous (hot and dry) summer season characteristic of the Mediterranean-type climate impose a constraint on noctuid life histories? (2) Are there detectable differences in abundance or phenological patterns between the noctuid assemblages feeding on evergreen and winter-deciduous trees and shrubs?
• 2 Regardless of their leaf persistence habit, the majority of woody species studied had short shoot growth and leaf production periods in spring. Abundance of noctuid larvae peaked in May-June, shortly after host plants started to produce new leaves. Virtually no noctuid larvae were found on the foliage of the woody species studied at other times of year. Abundance and seasonal pattern of occurrence of larvae were similar on evergreen and deciduous food plants.
• 3 In contrast with the unimodal seasonal pattern exhibited by larvae, the abundance of adult moths (assessed by light trapping) showed two distinct peaks in early summer and early autumn, and a marked minimum in mid-summer.
• 4 Most woody plant-feeding noctuids recorded in this study (86% of species, about 95% of individuals) were univoltine. Univoltine species fell into one of two distinct life history categories, corresponding to pre- and post-summer flight periods. These two contrasting phenologies were associated with a bimodality in the duration of the pupal stage (‘short’ versus ‘long’), and were closely related to taxonomical affiliation at the subfamily level.
• 5 Within the ‘short’ pupal duration group, some species mate and oviposit shortly after emergence and pass the dry season in the egg stage, while others remain as potentially active, non-reproductive adults over most of the summer and mate by the end of that season. Species in the ‘long’ pupal duration group pass the summer in pupal or prepupal stage.
• 6 In the Mediterranean habitats studied, the adversity of the summer dry season seems to have led to a woody plant-feeding noctuid species assemblage almost entirely made up of univoltine species that concentrate their larval phases when suitable food (young leaves) is most abundant, and ‘avoid’ mid-summer as a flight time by emerging either shortly before or shortly after the adverse summer drought period. Year-round foliage availability afforded by dominant evergreen plants does not seem to have influenced the seasonal organization of noctuid cycles in any substantial way.

     

Overlapping trophic niches among co‐occurring amphipods from a cryptic species complex

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Aversion and attraction to harmful plant secondary compounds jointly shape the foraging ecology of a specialist herbivore

Most herbivorous insect species are restricted to a narrow taxonomic range of host plant species. Herbivore species that feed on mustard plants and their relatives in the Brassicales have evolved highly efficient detoxification mechanisms that actually prevent toxic mustard oils from forming in the bodies of the animals. However, these mechanisms likely were not present during the initial stages of specialization on mustard plants ~100 million years ago. The herbivorous fly Scaptomyza nigrita (Drosophilidae) is a specialist on a single mustard species, bittercress (Cardamine cordifolia; Brassicaceae) and is in a fly lineage that evolved to feed on mustards only in the past 10–20 million years. In contrast to many mustard specialists, S. nigrita does not prevent formation of toxic breakdown products (mustard oils) arising from glucosinolates (GLS), the primary defensive compounds in mustard plants. Therefore, it is an appealing model for dissecting the early stages of host specialization. Because mustard oils actually form in the bodies of S. nigrita, we hypothesized that in lieu of a specialized detoxification mechanism, S. nigrita may mitigate exposure to high GLS levels within plant tissues using behavioral avoidance. Here, we report that jasmonic acid (JA) treatment increased GLS biosynthesis in bittercress, repelled adult female flies, and reduced larval growth. S. nigrita larval damage also induced foliar GLS, especially in apical leaves, which correspondingly displayed the least S. nigrita damage in controlled feeding trials and field surveys. Paradoxically, flies preferred to feed and oviposit on GLS‐producing Arabidopsis thaliana despite larvae performing worse in these plants versus non‐GLS‐producing mutants. GLS may be feeding cues for S. nigrita despite their deterrent and defensive properties, which underscores the diverse relationship a mustard specialist has with its host when lacking a specialized means of mustard oil detoxification.     

Diet of two commercially important shark species in the United Arab Emirates: milk shark,Rhizoprionodon acutus (Rüppell, 1837), and slit‐eye shark,Loxodon macrorhinus (Müller & Henle, 1839)

The diets of the milk shark, Rhizoprionodon acutus, and the slit‐eye shark, Loxodon macrorhinus, landed from the artisanal fishery in the Arabian Gulf waters of the United Arab Emirates were investigated to determine their dietary preferences. Stomach contents from 57 milk sharks and 53 slit eye sharks were collected from Abu Dhabi (R. acutus, n = 23), Dubai (R. acutus, n = 5; L. macrorhinus, n = 15) and Ras Al Khaimah (R. acutus, n = 29; L. macrorhinus, n = 38) during fishery surveys from January to May 2012. Prey items were identified to the lowest possible taxonomic level, grouped into five categories including ‘teleost fish’, ‘cephalopods’, ‘crustaceans’, ‘invertebrates’, and ‘other’. The diets of both species were described using the numeric, frequency and weight methods, and the index of relative importance (IRI). The majority of stomachs for both species had food, with 66.6% of milk shark stomachs and 90.5% of slit‐eye shark stomachs containing prey items, both dominated by small teleosts. Rhizoprionodon acutus fed on a wide variety of teleost species, primarily Engraulidae (anchovies) (28%), Gerreidae (mojarras) (5.6%) and Carangidae (jacks) (1.6%) with occasional crustacean and cephalopod prey (8%). On the other hand, L. macrorhinus seemed to have a preference for one species in terms of teleosts (anchovies) (35.1%) and fed on a wider variety of crustaceans and cephalopods (22.6%). There was little overlap in the diets of these two species, suggesting that they may either be using different habitats or that in these waters, the milk shark is a generalist species while the slit‐eye is a specialist feeder.     

A bodyguard or a tastier meal? Dying caterpillar indirectly protects parasitoid cocoons by offering alternate prey to a generalist predator

In some parasitic Hymenoptera the dying caterpillars remain attached or close to the parasitoid cocoons. It has been suggested that the caterpillars act as ‘bodyguards’ for the vulnerable cocoons and therefore protect them against predators and/or hyperparasitoids (the ‘usurpation hypothesis’). This hypothesis has been demonstrated in associations where the caterpillars remain active and/or aggressive after parasitism. However, in other associations the caterpillars are so physiologically depleted after parasitism that they are unable to physically defend the cocoons and instead sit atop them in a moribund state. In this study a generalist predator, the spined soldier bug, Podisus maculiventris Say (Hemiptera: Pentatomidae), was provided with cocoons of the gregarious endoparasitoid Cotesia glomerata L. and the solitary endoparasitoid Microplitis mediator Haliday (both Hymenoptera: Braconidae), in turn attended by their hosts, Pieris brassicae L. (Lepidoptera: Pieridae) and Mamestra brassicae L. (Lepidoptera: Noctuidae), respectively. Cotesia glomerata produces broods of up to 40 cocoons and the dying caterpillars sit atop the cocoons where they exhibit little response to physical stimuli. Previous studies reported that dying P. brassicae caterpillars were ineffective bodyguards against two species of hyperparasitoids. In both associations, the dying host caterpillars were significantly preferred as food by P. maculiventris over the parasitoid cocoons. However, in absence of caterpillars, the bugs readily attacked the C. glomerata cocoons. Alternatively, the survival of M. mediator was very low, irrespective of whether a caterpillar was present or not. Caterpillars attacked by M. mediator are several times smaller than those attacked by C. glomerata. Consequently, the predators ran out of food much more quickly in the former and switched from one prey to the other. We show that in some host–parasitoid associations the dying caterpillars provide more visually apparent or nutritionally superior prey, rather than acting as bodyguards.     

Trophic level and basal resource use of soil animals are hardly affected by local plant associations in abandoned arable land

Plants provide resources and shape the habitat of soil organisms thereby affecting the composition and functioning of soil communities. Effects of plants on soil communities are largely taxon‐dependent, but how different functional groups of herbaceous plants affect trophic niches of individual animal species in soil needs further investigation. Here, we studied the use of basal resources and trophic levels of dominating soil meso‐ and macrofauna using stable isotope ratios of carbon and nitrogen in arable fallow systems 3 and 14–16 years after abandonment. Animals were sampled from the rhizosphere of three plant species of different functional groups: a legume (Medicaco sativa), a nonlegume herb (Taraxacum officinale), and a grass (Bromus sterilis). We found virtually no consistent effects of plant identity on stable isotope composition of soil animals and on thirteen isotopic metrics that reflect general food‐web structure. However, in old fallows, the carbon isotope composition of some predatory macrofauna taxa had shifted closer to that of co‐occurring plants, which was particularly evident for Lasius, an aphid‐associated ant genus. Trophic levels and trophic‐chain lengths in food webs were similar across plant species and fallow ages. Overall, the results suggest that variations in local plant diversity of grassland communities may little affect the basal resources and the trophic level of prey consumed by individual species of meso‐ and macrofauna belowground. By contrast, successional changes in grassland communities are associated with shifts in the trophic niches of certain species, reflecting establishment of trophic interactions with time, which shapes the functioning and stability of soil food webs.     

Untangling the aphid-parasitoid food web in citrus: Can hyperparasitoids disrupt biological control?

Molecular techniques are irreplaceable to untangle the trophic links in communities where immature entomophagous species (either in the third or fourth level) develop inside the phytophagous. This is the case of aphid-parasitoid communities. Here, we develop a DNA-based approach to untangle the structure of the aphid-parasitoid food web in citrus, where Aphis spiraecola Patch. (Hemiptera: Aphididae) is a key pest and Binodoxys angelicae Haliday (Hymenoptera: Braconidae), its dominant primary parasitoid, is attacked by a complex of hyperparasitoids. Aphid populations and parasitism were followed at weekly intervals in 2012 and 2013. Parasitism rates were low (∼0.04 in the four sampled orchards). Simultaneously, colonies harboring aphid mummies were collected. Approximately half of the mummies were reared to adulthood and at least six hymenopteran hyperparasitoid species were identified by classical means: Syrphophagus aphidivorus (Mayr) (Encyrtidae), Alloxysta sp. (Forster) (Figitidae), Asaphes sp. (Walker) (Pteromalidae), Pachyneuron aphidis (Bouché) (Pteromalidae), Dendrocerus sp. (Ratzeburg) (Megaspilidae) and Phaenoglyphis villosa (Hartig) (Figitidae). The other half was subjected to a Taqman-based multiplex PCR to investigate trophic relationships in this food web. We confirmed that all six species hyperparasitized B. angelicae. The most abundant hyperparasitoids were S. aphidivorus and Alloxysta sp. Both were abundant from the beginning of the season, and hyperparasitism rates remained high (∼0.4) throughout the season in the two study years. Although these species could share the same mummy, S. aphidivorus and Alloxysta sp. were the most abundant species and dominated this food web. Finally, hyperparasitoids also increased the secondary sex ratio of B. angelicae. Thus, hyperparasitism probably explains the low impact of B. angelicae on A. spiraecola populations.     

Clear,crashing, turbid and back – long‐term changes in macrophyte assemblages in a shallow lake

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Distribution and influence of grazing on wheat curl mites (Aceria tosichella Keifer) within a wheat field

Wheat streak mosaic virus (WSMV) is a serious disease of wheat and is primarily transmitted from infected to healthy plants by the wheat curl mite, Aceria tosichella Keifer. Although wheat is the primary plant host of A. tosichella, wheat curl mites have been recorded on more than 60 different plant hosts; this broad host range allows mites to survive outside the wheat‐growing season by providing a ‘green bridge’. Despite the fact that A. tosichella can only crawl short distances, the mites can disperse via wind and thus have the capacity to readily infest wheat crops from neighbouring refuges. In this study, we undertook field trials to investigate the temporal movement of A. tosichella, as well as the importance of wind and livestock grazing on mite dispersal late in the cropping season. We demonstrate there is a window in spring when A. tosichella undergo significant movement in south‐eastern Australia, and this is likely related to the development stage of wheat plants, and may also be influenced by wind direction. We found that grazing wheat crops reduced mite numbers, suggesting that any increase in WSMV issues in ‘grain and graze’ crops is likely due to the longer season wheat varieties used in these systems rather than the direct effects of grazing. These results emphasize the importance of crop management strategies in the control of A. tosichella.     

Ecological diversity of edible insects and their potential contribution to household food security in Haut‐Katanga Province,Democratic Republic of Congo

Democratic Republic of the Congo (DR Congo) has a wide diversity of edible insects making it one of the most important biodiversity hot spots in Africa. The aim of this study was to give the first insight into the food plant range, seasonal availability of edible insects, community preference and willingness to consume them. The study revealed a list of eleven edible insect species belonging to four families. Twenty‐six plant species were recorded as food plants of nine edible caterpillar species. Seasonal availability of these insects coincided with the rainy season and was strongly linked to relatively high level of consumption. The caterpillars Elaphrodes lactea Gaede, Lobobunaea saturnus Fabricius and Cinabra hyperbius (Westwood) as well as the termites Macrotermes falciger Gerstäcker were the most dominant species of edible insects preferred and consumed among the different communities. Our study demonstrates that entomophagy is a common practice among the ethnic populations with married, tertiary and university‐level individuals recording significantly higher consumption of edible caterpillars. Populations between the ages of 18 and 45 years as well as the Bemba tribe were also more actively involved in entomophagy. Further research would be necessary to exploit edible insect biodiversity and ethno‐entomophagy and initiate actions for food plant conservation in DR Congo.     

Responses of the soil fungal communities to the co‐invasion of two invasive species with different cover classes

• Soil fungal communities play an important role in the successful invasion of non‐native species. It is common for two or more invasive plant species to co‐occur in invaded ecosystems.
• This study aimed to determine the effects of co‐invasion of two invasive species (Erigeron annuus and Solidago canadensis) with different cover classes on soil fungal communities using high‐throughput sequencing.
• Invasion of E. annuus and/or S. canadensis had positive effects on the sequence number, operational taxonomic unit (OTU) richness, Shannon diversity, abundance‐based cover estimator (ACE index) and Chao1 index of soil fungal communities, but negative effects on the Simpson index. Thus, invasion of E. annuus and/or S. canadensis could increase diversity and richness of soil fungal communities but decrease dominance of some members of these communities, in part to facilitate plant further invasion, because high soil microbial diversity could increase soil functions and plant nutrient acquisition. Some soil fungal species grow well, whereas others tend to extinction after non‐native plant invasion with increasing invasion degree and presumably time. The sequence number, OTU richness, Shannon diversity, ACE index and Chao1 index of soil fungal communities were higher under co‐invasion of E. annuus and S. canadensis than under independent invasion of either individual species.
• The co‐invasion of the two invasive species had a positive synergistic effect on diversity and abundance of soil fungal communities, partly to build a soil microenvironment to enhance competitiveness of the invaders. The changed diversity and community under co‐invasion could modify resource availability and niche differentiation within the soil fungal communities, mediated by differences in leaf litter quality and quantity, which can support different fungal/microbial species in the soil.

     

Adding floral nectar resources to improve biological control: Potential pitfalls of the fourth trophic level

The effects of floral nectar resources on ecosystem function were investigated by examining the consequences of increasing habitat complexity in field microcosms on the dynamics of a four-trophic-level community, consisting of lucerne (alfalfa), a herbivore (the pea aphid, Acyrthosiphon pisum), its parasitoid (Aphidius ervi) and a hyperparasitoid (Dendrocerus aphidum). The influence of buckwheat (Fagopyrum esculentum) flowers on the parasitism and hyperparasitism by A. ervi and D. aphidum, respectively, was compared with buckwheat-free treatments. Experimental units for this study were 1.8×1.8×2 m³ steel-framed cages covered with a fine mesh. Parasitism and hyperparasitism rates were significantly higher in the presence of flowering buckwheat. Parasitism rates by A. ervi were lower but not significantly, in the presence of D. aphidum in buckwheat and buckwheat-free treatments. A. pisum density was significantly reduced by A. ervi when buckwheat was present, but the density of the aphid was not affected by the hyperparasitoid. The parasitoid's potential to reduce the host population was, therefore, significantly influenced by the presence of floral nectar. Although hyperparasitism rates were significantly increased by buckwheat, this did not ‘cascade’ to the second trophic level, the pea aphid. However, before floral resources are deployed in agro-ecosystems to enhance biological control of pests, the influence of flowers on the second and fourth trophic levels should always be considered.