Aphidophagous Hoverflies Research Articles

Temperature-dependent Prey Consumption and Functional Response of Episyrphus balteatus De Geer (Diptera: Syrphidae) to Macrosiphum rosae L. (Homoptera: Aphididae) reared on Rosa alba L. under Laboratory Conditions

Laboratory experiments were conducted to determine the prey consumption and functional response of the aphidophagous hoverfly Episyrphus balteatus DeGeer (Diptera: Syrphidae) to different densities of fourth instar rose aphids, Macrosiphum rosae (Homoptera: Aphididae), reared on Rosa alba L. (Rosaceae) at 20 oC, 27 oC and 35 oC. The third instar of E.balteatus consumed a maximum of 51.3±0.53 M. rosae aphids at 27 oC, followed by the third instar with 46.5±0.53 aphid predation at 20 oC. The lowest handling time (Th) was noted for the third instar larvae of E. balteatus (0.407± 0.012) at 27 oC, and the maximum handling time (Th) of (0.662 ± 0.024) was noted for 2nd larvae of E. balteatus at 35 oC. The highest attack rate was noted for 3rd instar larvae (0.201± 0.014) at 27 oC, while the lowest attack rate was noted for second instar at 35 oC. Both instars of Episyrphus balteatus exhibited type II functional response at all three temperatures.

Genome of the hoverfly Eupeodes corollae provides insights into the evolution of predation and pollination in insects

BackgroundHoverflies (Diptera: Syrphidae) including Eupeodes corollae are important insects worldwide that provide dual ecosystem services including pest control and pollination. The larvae are dominant predators of aphids and can be used as biological control agents, and the adults are efficient pollinators. The different feeding habits of larvae and adults make hoverflies a valuable genetic resource for understanding the mechanisms underlying the evolution and adaptation to predation and pollination in insects.ResultsHere, we present a 595-Mb high-quality reference genome of the hoverfly E. corollae, which is typical of an aphid predator and a pollinator. Comparative genomic analyses of E. corollae and Coccinellidae (ladybugs, aphid predators) shed light on takeout genes (3), which are involved in circadian rhythms and feeding behavior and might regulate the feeding behavior of E. corollae in a circadian manner. Genes for sugar symporter (12) and lipid transport (7) related to energy production in E. corollae had homologs in pollinator honeybees and were absent in predatory ladybugs. A number of classical cytochrome P450 detoxification genes, mainly CYP6 subfamily members, were greatly expanded in E. corollae. Notably, comparative genomic analyses of E. corollae and other aphidophagous hoverflies highlighted three homologous trypsins (Ecor12299, Ecor12301, Ecor2966). Transcriptome analysis showed that nine trypsins, including Ecor12299, Ecor12301, and Ecor2966, are strongly expressed at the larval stage, and 10 opsin genes, which are involved in visual perception, are significantly upregulated at the adult stage of E. corollae.ConclusionsThe high-quality genome assembly provided new insights into the genetic basis of predation and pollination by E. corollae and is a valuable resource for advancing studies on genetic adaptations and evolution of hoverflies and other natural enemies.

Time since establishment drives bee and hoverfly diversity, abundance of crop-pollinating bees and aphidophagous hoverflies in perennial wildflower strips

Wildflower strips (WFS) are amongst the most commonly applied measures to promote pollinators and natural enemies of crop pests in agroecosystems. Their potential to enhance these functionally important insect groups may vary substantially with time since establishment of WFS. However, knowledge on their temporal dynamics remains scarce, hampering recommendations for optimized design and management. We therefore examined temporal dynamics of taxonomic and functional groups of bees and hoverflies in perennial WFS ranging from one to ≥6 years since sowing with a standardized species-rich seed mixture of flowering plants in 18 agricultural landscapes in Switzerland. The abundance of wild bees, honeybees and hoverflies declined after the second year by 89%, 62% and 72%, respectively. Declines in bee abundance and hoverfly species richness were linear and those of aphidophagous hoverflies exponential, while wild bee species richness peaked in the third year. Declines over time generally paralleled decreases in flower abundance (-83%) and flowering species richness (-61%) and an increase in grass cover (+70%) in WFS. Flowering plant species richness showed strong positive relationships with dominant crop-visiting wild bees and aphidophagous hoverflies. Furthermore, dominant crop-visiting wild bees, but not aphidophagous hoverflies, were positively related to the proportion of (semi-)open semi-natural habitat in the surrounding landscape (500 m radius), but negatively with forest. We conclude that the effectiveness of perennial WFS to promote pollinator diversity, crop-pollinating bees and aphidophagous hoverflies through foraging resources decreases after the first two to three years, probably due to a decline of diverse and abundant floral resources. Although older perennial WFS may still provide valuable nesting and overwintering opportunities for pollinators and natural enemies, our findings indicate that regular re-sowing of perennial WFS may be necessary to maintain adequate floral resource provisioning for effective pollinator conservation and promotion of crop pollination and natural pest control services in agricultural landscapes.

Life cycle, population parameters, and predation rate of the hover fly Eupeodes corollae fed on the aphid Myzus persicae

AbstractTo improve the effectiveness of biological control procedures, it is necessary to quantify the survival rate of a natural enemy through the various stages of the life cycle, the fecundity rate, and the predation rate from birth to death. It is not only important to obtain all the parameters associated with a life table, but also to quantify the predation rate in the life table framework. For this purpose, the life history, population parameters, and predation rate of Eupeodes corollae (Fabricius) (Diptera: Syrphidae) were determined using Myzus persicae (Sulzer) (Hemiptera: Aphididae) as prey and the age‐stage, two‐sex life table methods. As predators released in biocontrol programs are mass‐produced from small populations with a consequent loss of genetic variability, we used specimens from a laboratory colony with similar characteristics. The highest mortality was found in the egg stage (54%). The mean developmental time of the pre‐adult stage was 13.70 ± 0.08 days. In the adult stage, the mean longevity was 23.81 ± 1.14 days, with the males living longer than the females. The total pre‐oviposition period was 17.62 ± 0.45 days and the mean female fecundity was 169.81 ± 29.65 eggs per female. The population parameters indicated that the population grew with a net reproduction rate of 32.87 ± 7.25 offspring per individual and an average generation time of 23.05 ± 0.65 days. The values related to the number of aphid nymphs consumed by the larvae were: a mean predation rate (cxj) of 485.20 ± 11.61 nymphs, a net predation rate (C0) of 216.68 ± 16.89, and a finite predation rate (ω) of 28.03 ± 1.18. The obtained results support the use of E. corollae as valuable resource in the biological control of aphids, specifically M. persicae. Moreover, the technique implemented in this paper allows the objective comparison of E. corollae capacity as control agent with that of other aphidophagous hover fly species and other aphid natural enemies.

Aphidophagous hoverflies reduce foxglove aphid infestations and improve seed set and fruit yield in sweet pepper

Larvae of many hoverfly species prey upon aphids, whereas the adults, by relying on nectar and pollen, contribute to the pollination of many plant species. Despite their great potential for pest control and pollination, important gaps still exist regarding the efficacy of hoverflies in regulating infestations of major aphid pests in augmentative biological control programs. Here, we tested the potential of the commercially available hoverflies Eupeodes corollae and Sphaerophoria rueppellii to regulate populations of the foxglove aphid Aulacorthum solani in sweet pepper. In a semi-field experiment, aphid numbers were 93.2% and 78.4% lower in the E. corollae and S. rueppellii treatments, respectively, compared to the control. Fruit yield was increased by 390% and 361% and seed set by 395% and 399% for E. corollae and S. rueppellii. In a separate laboratory trial, we found that under conditions of limited prey, hoverfly larvae did not complete development, but that larvae of S. rueppellii survived significantly longer than larvae of E. corollae. We have shown for the first time that E. corollae and S. rueppellii can reduce infestations of foxglove aphid in sweet pepper. The limited amount of prey, related to the small size of the A. solani colonies, means that hoverfly larvae were often not able to complete development. In practice, repeated releases of hoverflies, possibly in combination with other natural enemies, might be used to achieve effective suppression of A. solani infestations. © 2021 Society of Chemical Industry.

Spatio-temporal variation of predatory hoverflies (Diptera: Syrphidae) and their relationship with aphids in organic horticultural crops in La Plata, Buenos Aires

Population variations of predatory hoverflies in agroecosystems depend mainly on the resources that crops and wild vegetation provides them as well as death caused by natural enemies. We identified I) aphidophagous hoverfly species in lettuce and broccoli crops in Buenos Aires, II) the seasonal variations of the immature stages and their larval parasitism, and III) the wild plants, surrounding the crops, visited by adults. Fortnightly, 30 leaves were randomly selected in both crops during 2018-2019 and immature stages of syrphids and aphids per leaf were recorded. Adults were manually collected in patches of the wild plants (during 10 min of direct observations), and plants visited by adults were determined. The hoverflies were Allograpta exotica Wiedemann and Toxomerus duplicatus Wiedemann. Only A. exotica was recorded in crops. The dominant aphids were Myzus persicae (Sulzer) in lettuce and Brevycorine brassicae (L.) in broccoli. Parasitism rates ranged between 8 and 100% and the species were Diplazon laetatorius (Fabricius), in both crops, and Pachyneuron aff. nelsoni only in broccoli. Galinsoga parviflora Cav. and Matricaria chamomilla L. were the wild plants most often visited by hoverflies. This work provides basic information for the control of aphids by hoverflies in the framework of conservation biological control

Cinara splendens (Hemiptera: Aphididae: Lachninae)—First Record in Palaearctic Region

Nearctic aphid Cinara splendens (Gillette and Palmer, 1924) was collected on ornamental Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) in South Bohemia in 2009. It was the first record of this species in the Palaearctic region. The aim of this research was to study the bionomy of this species in Central Europe and to make descriptions of all available morphs, as previous morphological descriptions of C. splendens appeared to be incomplete. Six monitoring sites of this species were established in South Bohemia and were then regularly attended in the period of 2009–2019. The colonies of C. splendens were observed; its natural enemies and honeydew users were also registered. Aphids were collected for the microscope slide preparation, followed by the evaluation of thirty of the basic quantitative and seven qualitative morphological characteristics. Partial sequences of mitochondrial COI and nuclear EF-1α were used to confirm morphology-based identification and to compare samples from the Czech Republic with those of North American origin. Cinarasplendens survived successfully under new ecological conditions, but its population density remained quite low, except for 2009 and 2019, due to a synergistic effect of the dry weather and very high population density of the adelgid Gilletteella coweni (Gillette, 1907), which is a key pest of Douglas fir in the Czech Republic. The principle predators were coccinellid beetles, while the aphidophagous hover flies were less abundant. Together with a weak ability to migrate due to a low number of alate viviparous females in population, C. splendens cannot be a potential pest of P. menziesii in Central Europe.

One stone; two birds: concurrent pest control and pollination services provided by aphidophagous hoverflies

Biological pest control and pollination are vital ecosystem services that are usually studied in isolation, given that they are typically provided by different guilds of arthropods. Hoverflies are an exception, as larvae of many aphidophagous species prey upon agriculturally important aphid pests, while the adults feed on floral nectar and pollen and can be effective pollinators of important agricultural crops. While this is widely known, the concurrent provisioning of pest control and pollination by aphidophagous hoverflies has never been studied. Here, we compared the potential of two aphidophagous hoverflies, Eupeodes corollae and Sphaerophoria rueppellii to concurrently control the aphid Myzus persicae and improve pollination (measured as seed set and fruit weight) in sweet pepper (Capsicum annuum). In a first semi-field experiment, aphid populations were reduced by 71 and 64% in the E. corollae and S. rueppellii treatments, respectively, compared to the control. In a second experiment, the aphid population reduction was 80 and 84% for E. corollae and S. rueppellii, respectively. Fruit yield in aphid-infested plants, was significantly increased by 88 and 62% for E. corollae and S. rueppellii, respectively, as compared to the control. In a separate trial, where the plants were not infested with aphids, yield increased by 29 and 11% for E. corollae and S. rueppellii, respectively, even though these differences were not statistically significant. The increase in seed set in the hoverfly treatments was statistically significant in both pollination experiments, i.e. independently of the presence of aphids. These results demonstrate, for the first time, that aphidophagous hoverflies can concurrently provide pest control and pollination services.

Stability and changes in the distribution of Pipiza hoverflies (Diptera, Syrphidae) in Europe under projected future climate conditions.

Climate change is now considered a significant threat to terrestrial biodiversity. Species distribution models (SDMs) are among the modern tools currently used to assess the potential impacts of climate change on species. Pipiza Fallén, 1810 is a well known aphidophagous hoverfly genus (Diptera, Syrphidae) at the European level, for which sampling has been conducted across the region, and long-term databases and geo-referenced datasets have been established. Therefore, in this work, we investigated the potential current distributions of the European species of this genus and their response to future climate change scenarios, as well as evaluated stability in their ranges and potential changes in species-richness patterns. We applied three climate models (BCC_CSM1.1, CCSM4, HadGEM2-ES) to four representative concentration pathways (RCP 2.6, RCP 4.5, RCP 6.0, RCP 8.5) for two time frames (2050 and 2070). Our results show that the distribution of most Pipiza species may slightly differ under different climate models. Most Pipiza species were predicted not to be greatly affected by climate change, maintaining their current extent. Percentages of stable areas will remain high (above 50%) for the majority of studied species. According to the predicted turnover of species, northern Europe, could become the richest in terms of species diversity, thus replacing Central Europe as the current hot spot.

Host plant range of Aphidophagous hoverflies in relation to their prey aphids in Badin, Sindh, Pakistan.

Aphidophagous hoverflies are one of the significant groups of family syrphidae for their larvae as well as adults, larvae feed on many insect pests i.e. aphids, jassids, thrips, which mainly infest several crops such as brassica, spinach, rice, wheat etc., whereas their adults are very important pollinators for these crops. This study was carried out to identify the hoverfly species which can be used as pest control of various agricultural crops grown in Badin which is a monsoon climatic region and main agricultural area of Sindh coastal line where a variety of flowering crops, fruits and vegetables are cultivated; and these include mango, banana, guava, lemon, jojoba, sugarcane, reddish, brassica, wheat, rice, okra, cabbage, chilli, cucumber, sunflower, tomato, onion etc. This study was conducted in the various farming fields of district Badin during the cropping season from January-April 2017. As a result a total of 253 specimens of 2 species, Sphaerophoria scripta and Episyrphus balteatus belonging to genus Sphaerophoria and Episyrphus were trapped by the help of insect hand net and malaise trap. Out of these 253 specimens, 34 were male and 219 were female. Pearson correlation analysis showed that there was strong positive and significant correlation of hoverflies population with the number of host plants as well as number of aphid colonies per month the values being r =.820 (p= 0.012) and r = .875 (p= 0.01) respectively. Keywords: Aphidophagous hoverflies; Aphids; Badin; Host plants; Pakistan; Prey; Sindh http://dx.doi.org/10.19045/bspab.2019.80065

Foraging Behavior of an Aphidophagous Hoverfly, Sphaerophoria macrogaster (Thomson) on Insectary Plants.

Flower resources are prerequisites for survival and reproduction of aphidophagous hoverflies adults. It is, therefore, necessary to evaluate their foraging behavior with regards to different flowering species in order to utilize hoverflies to enhance conservation biological control (CBC) of aphids. The foraging behavior of the female hoverfly, Sphaerophoria macrogaster (Thomson) was observed in coriander (Coriandrum sativum Linnaeus) and blue salvia (Salvia farinacea Bentham) flower patches using a focal sampling method combined with continuous recording. The sequences and durations of all foraging bouts were recorded during the residence of observed S. macrogaster in each flower patch. Significantly more transitions from searching to assessment of flowers were noted in coriander than in blue salvia flower patches (χ2 = 4.55, p<0.05). However, approaching to probing transitions were significantly more frequent in blue salvia than in coriander flower patches (χ2 = 9.59, p<0.05). Foragers showed significantly prolonged inter plant movement but shorter probing durations in coriander flower patches. Of interest, total duration of time spent in patches by S. macrogaster did not differ significantly between coriander and blue salvia. Results from the present study illustrated that both flowering plant species were apparently attractive to Sphaerophoria macrogaster females but these foragers preferred coriander flowers. This finding may form the basis of flower selection in and around the crop fields for enhancement of this aphidophagous natural enemy to maximize the biological control of aphids.

Dealing with food shortage: larval dispersal behaviour and survival on non‐prey food of the hoverfly Episyrphus balteatus

1. Predatory larvae often have to face food shortages during their development, and thus the ability to disperse and find new feeding sites is crucial for survival. However, the dispersal capacity of predatory larvae, the host finding cues employed, and their use of alternative food sources are largely unknown. These aspects of the foraging behaviour of the aphidophagous hoverfly (Episyrphus balteatus De Geer) larvae were investigated in the present study.2. It was shown that these hoverfly larvae do not leave a plant as long as there are aphids available, but that dispersing larvae are able to find other aphid colonies in the field. Dispersing hoverfly larvae accumulated on large aphid colonies, but did not distinguish between different pea aphid race–plant species combinations. Large aphid colonies might be easier to detect because of intensified searching by hoverfly larvae following the encounter of aphid cues like honeydew that accumulate around large colonies.3. It was further shown that non‐prey food, such as diluted honey or pollen, was insufficient for hoverfly larvae to gain weight, but prolonged the survival of the larvae compared with unfed individuals. As soon as larvae were switched back to an aphid diet, they rapidly gained weight and some pupated after a few days. Although pupation and adult hatching rates were strongly reduced compared with hoverflies continuously fed with aphids, the consumption of non‐prey food most probably increases the probability that hoverfly larvae find an aphid colony and complete their development.

Landscape complexity promotes hoverflies across different types of semi‐natural habitats in farmland

Abstract Semi‐natural habitats (SNH) provide essential resources for many organisms in agricultural landscapes and can increase biodiversity at the local and landscape scale. For the management of ecosystem services, it is crucial to understand how local characteristics of SNH and the surrounding landscape complexity affect beneficial species. We investigated this for hoverflies (Diptera: Syrphidae)—an important functional group providing both pest control and pollination services—in a total of 138 SNH within 35 agricultural landscapes in Switzerland and Germany. SNH differed in type (woody, herbaceous), shape (areal, linear) and availability of food resources (floral resources and aphids). They were located along a gradient of landscape complexity (1%–75% SNH in a 1 km radius). In total, 9,030 hoverflies belonging to 89 species were collected. In both countries, hoverfly community composition was mainly driven by SNH type and SNH shape, in addition to landscape complexity in Switzerland. Species richness of hoverflies increased with additional SNH at the landscape scale. However, the ubiquitous and dominant aphidophagous species Episyrphus balteatus was indifferent to landscape composition. Species richness of total and aphidophagous hoverflies was higher in woody than in herbaceous SNH. Hoverfly species richness was similar in linear and areal SNH, but non‐aphidophagous hoverflies were more vulnerable to landscape simplification in linear than areal SNH. Effects of the SNH type partly differed between the two countries. In Germany, the dominant aphidophagous species E. balteatus preferred woody over herbaceous SNH, while no such difference was found in Switzerland. Overall, local richness and abundance of floral resources were poor predictors for hoverfly abundance, richness or community composition. Synthesis and applications. Hoverfly species richness and community composition in semi‐natural habitats (SNH) were mainly driven by the SNH type and landscape complexity. Conservation and restoration of complex agricultural landscapes with a high proportion of different SNH types is therefore key for the conservation of hoverfly diversity, and thus likely to promote pest control and pollination services provided by them. Thereby, local improvement of SNH to promote hoverflies has to consider regional differences in habitat characteristics.

Syrphine hoverflies are effective pollinators of commercial strawberry

Recent declines in wild pollinators represent a significant threat to the sustained provision of pollination services. Insect pollinators are responsible for an estimated 45% of strawberry crop yields, which equates to a market value of approximately £99 million per year in the UK alone. As an aggregate flower with unconcealed nectaries, strawberries are attractive to a diverse array of flower-visiting insects. Syrphine hoverflies, which offer the added benefit of consuming aphids during their predatory larval stage, represent one such group of flower visitor, but the extent to which aphidophagous hoverflies are capable of pollinating strawberry flowers remains largely untested. In replicated cage experiments we tested the effectiveness of strawberry pollination by the aphidophagous hoverflies Episyrphus balteatus and Eupeodes latifasciatus, and a mix of four hoverfly taxa, when compared to hand pollination and insect pollinator exclusion. Hoverflies were released into cages, and the strawberry fruits that resulted from pollinated flowers were assessed for quality measures. Hoverfly visitation increased strawberry yields by over 70% and doubled the proportion of marketable fruit, highlighting the importance of hoverflies for strawberry pollination. A comparison between two hoverfly species showed that Eupeodes latifasciatus visits to flowers produced marketable fruit at nearly double the rate of Episyrphus balteatus, demonstrating that species may differ in their pollination efficacy even within a subfamily. Thus, this study offers compelling evidence that aphidophagous syrphine hoverflies are effective pollinators of commercial strawberry and, as such, may be capable of providing growers with the dual benefit of pollination and aphid control.

The influence of forest management on the abundance and diversity of hoverflies in commercial plantations of Sitka spruce: the importance of sampling in the canopy

Abstract The majority of Sitka spruce plantations in the UK are managed by clear-cutting and replanting, which leads to the formation of relatively large blocks (5–30 ha) of even-aged, closely spaced trees. These stands are considered to be poor in terms of general biodiversity and vulnerable to outbreaks of insect pests and diseases. In contrast, stands managed using alternative silvicultural systems, such as shelterwood or group selection systems, contain a wider range of tree ages and sizes and have the potential to support greater numbers of other species. If this includes the natural enemies (predators, parasitoids) of pest species, then adopting alternative silvicultural systems might help to reduce current and future pest impacts. To determine whether the greater structural complexity of stands managed using alternative silvicultural systems is associated with an increase in insect diversity and an increase in the abundance of predatory species, we sampled hoverflies (Diptera: Syrphidae) in 5 shelterwood stands, 6 group selection stands and 13 even-aged stands of Sitka spruce at 4 forest sites in mid and north Wales. The larvae of aphidophagous hoverflies are important invertebrate predators in spruce plantations, and hoverfly species richness is often used as an indicator of general invertebrate diversity. Hoverflies were sampled at ground level and in the canopy using yellow pan traps and flight interception traps. 7323 adult hoverflies of 74 species were captured, the majority of these in traps in the canopy. Total hoverfly abundance and the abundance of aphidophagous species were significantly higher ( P

Eupeodes luniger (Diptera, Syrphidae) a new record to Greece and a key for the genus Eupeodes in this country

Eupeodes luniger (Meigen, 1822) (Diptera, Syrphidae), an aphidophagous hoverfly species that acts also as pollinator, was recorded for the first time in Greece. Based on the Greek records, we provide the first identification key for the genus Eupeodes Osten Sacken, 1877 in Greece.

Pest regulation and support of natural enemies in agriculture: Experimental evidence of within field wildflower strips

Restoring ecosystem services in agriculture is vital to reach a sustainable food production. More specifically, developing farming practices which enhance biological pest control is a main issue for today’s agriculture. The aim of this study was to assess whether the two strategies of complicating the search of host plants by pests by increasing plant diversity, and of supporting their natural enemies by managing habitats, could be combined simultaneously at the field scale to restore biological pest control and reduce chemical insecticide use. In Gembloux (Belgium), wildflower strips (WFS) were sown within wheat crops in which pests (i.e., aphids), their predators (i.e. aphidophagous hoverflies, lacewings and ladybeetles) and parasitoid wasps were monitored for 10 weeks in the period of May through July 2015 as indicators of the ES of pest control. Aphids were significantly reduced and adult hoverflies favoured in wheat in between WFS, compared to monoculture wheat plots. No significant differences were observed for adult lacewings, ladybeetles and parasitoids. In all treatments, very few lacewing and ladybeetle larvae were observed on wheat tillers. The abundance of hoverfly larvae was positively correlated with the aphid density on tillers in between WFS, showing that increasing food provisions by multiplying habitats within fields, and not only along margins, can help supporting aphidophagous hoverflies in crops. By enhancing the ecosystem services of biological pest control, this study shows that increasing both plant diversity and managing habitats for natural enemies may reduce aphid populations, hence insecticide use. Future research should continue this vein of work by quantifying the link between agricultural practices and the delivery of ecosystem services in order to guide future measures of agricultural policies.

&lt;b&gt;Distance from the edge of forest fragments influence the abundance of aphidophagous hoverflies (Diptera: Syrphidae) in wheat fields

This study aimed to evaluate the influence of the distance from the edge of native forests on the abundance of aphidophagous hoverflies in wheat fields. The study was conducted in four commercial fields in the North of Parana State, Brazil, during the wheat crop season of 2009. Two transects were surveyed parallel to the edge of the forest at two distances: 25 (near) and 525 meters (far) from the edge. The abundance of hoverflies was compared using a χ 2 test (p ≤ 0.05). In total, 1,845 hoverflies adults were collected, which represented 15 species and three genera. The most abundant species was Allograpta exotica (60.43%), followed by Toxomerus dispar (17.78%) and Toxomerus watsoni (7.26%) (Diptera: Syrphidae). An important inference was that all fields showed a higher abundance of aphidophagous hoverflies closer to the edge of the forest (25 m) during the wheat tillering stage. The initial abundance of aphidophagous hoverflies in wheat fields is likely greater near the edge because of the availability of resources in the surrounding forest that enhance hoverfly survival during periods of low aphid infestation.

Oviposition preference of aphidophagous hoverflies toward oviposition site quality: The presence of intra- and interspecific competitor, glucosinolate content, and prey species

The selection of oviposition sites by aphidophagous insects is complex because of tritrophic interactions among host plant, aphid, and natural enemies. Several factors are known to affect the choice of oviposition site by aphidophagous hoverflies. The decisions of ovipositing females about where to lay their eggs are even more important in insects whose newly hatched offspring have limited dispersal ability, such as most aphidophages. In this study, we focused on the oviposition responses of two generalist aphidophagous syrphids (Eupeodes luniger and Episyrphus balteatus) toward host plant–aphid combinations differing in sinigrin content and the presence of intra- and interspecific competitors. The oviposition preference of Eupeodes luniger was significantly influenced in a reverse manner by the presence of intraguild competitors and also by the sinigrin content of host plants (P<0.0001 for both factors). Likewise, the overall proportion of eggs laid by female Episyrphus balteatus was greater on aphids with relatively low levels of sinigrin. Our findings help in understanding the factors governing the oviposition responses of aphidophagous predators.

Spillover of tachinids and hoverflies from different field margins

The introduction and conservation of field margins have been proposed as an intervention to counteract the decline in farmland biodiversity. However, how these margins can affect the movement of species and individuals (i.e. spillover) of natural enemies between field margins and crop is still unclear. In this work, we investigated the spillover of two different groups of natural enemies: tachinids (Diptera: Tachinidae) and aphidophagous hoverflies (Diptera: Syrphidae). For comparison we also investigated the response of non-aphidophagous hoverflies. We examined the spillover from two types of field margin (grass margin vs. hedgerow+grass margin) to adjacent maize fields located in landscapes with different proportion of arable land. The spillover of natural enemies was affected by the field margins, but the response varied between insect groups. The spillover of tachinids was higher from the grass margin than from hedgerows, suggesting that the spillover of this group may be related to the low contrast between the vegetation structure of the margin and the crop. In contrast to tachinids, the abundance of aphidophagous hoverflies was higher toward the center of the crop field, independently of the type of field margin. The spillover of non-aphidophagous hoverflies was not affected by the type of field margin. These species were only affected by the landscape composition as their species richness and abundance were higher in landscapes with low amounts of arable land. Measures focusing on the creation and management of field margins need to consider the local contrast between field margins and crops in relation to the life-history traits of different taxa.