Cold tolerance of the aphid predator Episyrphus balteatus (DeGeer) (Diptera, Syrphidae)

Abstract. Larvae of the hoverfiy Episyrphus balteatus (DeGeer) are important predators of aphids in the U.K. A large proportion of the U.K. population migrates south to warmer climes at the end of summer, but a small number are thought to overwinter in the U.K., with the mated female being the overwintering morph. The cold tolerance of adult flies was investigated to assess the overwintering potential of E. balteatus in the U.K. The high supercooling point (SCP) of -8.3 ± 0.7°C, and lethal temperature (LTemp₃₀) of -9.1°C for acclimated females suggest that E. balteatus has limited cold hardiness. This was confirmed by experiments where, despite a strong acclimation response in both males and females, there was no long-term survival at 5, 0 or - 5°C. At 5°C, 90% of females had died after 10 days. The weak cold hardiness of adult E. balteatus was corroborated by field experiments which demonstrated a 100% mortality after 10 weeks' exposure to U.K. winter conditions. The ecological significance of this limited cold hardiness is discussed in relation to the overwintering abilities of E. balteatus in the U.K.     

Developmental threshold, day-degree requirements and voltinism of the aphid predator Episyrphus balteatus (Diptera: Syrphidae)

Episyrphus balteatus is the dominant syrphid predator of aphids in the UK, reestablishment of populations each season is mainly by migration from warmer climes, as overwintering in this country is minimal with an uncertain level of success. The effects of temperature on the developmental rate of E. balteatus were investigated to determine the potential voltinism of this species in the UK. Estimates of the developmental threshold temperature from oviposition to adult emergence varied between 6.0d?C and 7.1d?C with a day-degree (DD) requirement of between 256 and 280 depending on the method of analysis used. Using the DD requirement derived from a weighted linear regression (261 DD above a threshold of 6.8d?C) in combination with the required value from adult emergence to first oviposition, suggests a total requirement of approximately 374 DD above 6.8d?C per generation. These data, together with climate records, indicate that one to three generations are possible each year, depending on the available DD and origin of the population. The advantages and limitations of different approaches and models used to estimate developmental thresholds and DD requirements are discussed.     

Susceptibility of the woolly apple aphid parasitoid,Aphelinus mali (Hym.: Aphelinidae), to common pesticides used in apple orchards in Israel

The effects of one acaricide (cyhexatin), two fungicides (penconazole and sulfur), and six insecticides (azinphos-methyl, chlorpyrifos, imidacloprid, pirimicarb, triazamate and vamidothion) on the adult stage of the parasitoidAphelinus mali (Haldeman), a parasite of the woolly apple aphidEriosoma lanigerum (Hausmann), were investigated under laboratory conditions. Chlorpyrifos (an organophosphorus insecticide-OP) was found to be highly toxic to the adult wasps. Vamidothion (OP) was more toxic to the parasitoid than azinphos-methyl (OP). On the other hand, both chlorpyrifos and azinphos-methyl were found to be harmless to the immature stages of the parasitoid in a test conducted under semi-field conditions. Of the other insecticides, imidacloprid was more toxic to the adult parasitoid than pirimicarb and triazamate. Neither cyhexatin nor penconazole had a considerable toxic effect upon the parasitoid. In contrast, sulfur was found to be moderately toxic to the parasitoid under laboratory conditions, as well as in a field survey in which we followed populations ofE. lanigerum andA. mali parasitization in sulfur-treated plots, and in a plot treated withAmpelomyces quisqualis Ces., a fungus antagonist to powdery mildew. The implications of these results to IPM programs of apple orchards in Israel are discussed     

烟粉虱天敌日本刀角瓢虫的捕食行为

研究了日本刀角瓢虫雌成虫和幼虫捕食粉虱时的各种行为时间分配.结果表明,日本刀角瓢虫成虫的捕食行为可分为爬行、取食、清洁、静息、整翅和排泄6个部分.饥饿后的日本刀角瓢虫幼虫捕食烟粉虱卵时,幼虫各龄期间的取食和爬行时间无显著差异,对烟粉虱卵的处置时间随瓢虫幼虫虫龄的增大而缩短.日本刀角瓢虫雌成虫捕食烟粉虱卵时,饥饿后的雌成虫用于取食的时间显著长于非饥饿的雌成虫,而用于清洁、静息和爬行的时间显著短于非饥饿的雌成虫;饥饿后的瓢虫雌成虫对卵的处置时间显著长于非饥饿的雌成虫.饥饿后的日本刀角瓢虫雌成虫捕食烟粉虱若虫时,瓢虫雌成虫的取食时间随烟粉虱若虫虫龄的增大而增加,清洁和静息时间随烟粉虱若虫虫龄的增大而缩短,对若虫的处置时间随烟粉虱若虫虫龄的增大而增加.     

Role of aphid predator guild in controlling spirea aphid populations on apple in West Virginia,USA

Spirea aphid populations and their predators were studied on apple to identify predators of importance in controlling aphid populations. Methods included random and non-random sampling from apple orchards in West Virginia, USA, sentinel aphid colonies, laboratory feeding studies, and predator exclusion studies. Aphidoletes aphidimyza (Diptera: Cecidomyiidae), chrysopids (Neuroptera: Chrysopidae), Harmonia axyridis (Coleoptera: Coccinellidae), and Orius insidiosus (Hemiptera: Anthocoridae) were the most abundant predators associated with spirea aphid colonies on apple. Parasitoids were all but absent in the study. Abundance of all predators was density dependent with greater responses to aphid populations at the orchard scale than to tree or individual colony scales. A. aphidimyza, O. insidiosus, chrysopids, and syrphids (Diptera) had the greatest degree of density dependence on aphid populations, and spiders showed inverse density dependence. Exclusion of predators with both cages and insecticides produced significantly higher aphid populations. Because of high abundance, good synchrony with aphid populations, and high impact per individual, H. axyridis adults were the most important spirea aphid predator on apple.     

A semi-synthetic diet for rearing Dipha aphidivora (Lepidoptera: Pyralidae), a promising predator of woolly aphid in sugarcane

Dipha aphidivora (Meyrick), a lepidopteran predator of sugarcane woolly aphid (SWA) Ceratovacuna lanigera Zehntner was successfully reared for three successive generations, for the first time on a freeze-dried beef liver-based larval semi-synthetic diet. We compared biological parameters viz., larval survival, adult weight, pre-and oviposition period, fertility, fecundity and female longevity of D. aphidivora reared on the semi-synthetic diet with the predators reared on SWA. Development time of larvae reared from first instar to pupation was 20.6 days on the semi-synthetic diet and 12 days on SWA, while survival of the larvae to adults was 61.8 and 91.8% on larval semi-synthetic diet and SWA, respectively. Fecundity recorded from semi-synthetic diet (41 eggs/female) was significantly less than those produced on SWA (58 eggs/female). However, fertility and longevity of the predators reared on SWA and semi-synthetic diet did not differ significantly. The study revealed the possibility of rearing D. aphidivora larvae using synthetic diet.     

The relationship between aphid infestations and oviposition by aphidophagous Syrphidae (Diptera)

Oviposition by aphidophagous Syrphidae varies with the size of aphid infestations and different syrphid species have different optimum aphid population sizes for oviposition. In one experiment using potted brussels sprout plants infested with Brevicoryne brassicae L., Platycheirus manicatus (Meig.) preferred about 100 aphids per plant, P. scutatus (Meig.) about 1000 aphids per plant and Syrphus ribesii (L.) about 2000 aphids per plant. These preferences were less clear in certain Platycheirus species (e.g. P. peltatus (Meig.)), than in Syrphus species (e.g. S. luniger Meig.). Once a plant has been selected for oviposition there may still be selection of suitable colonies on that plant. For a given aphid population, S. luniger preferred a small number of large aggregates to a larger number of smaller ones, whereas S. balteatus (Deg.) preferred the opposite. The tendency of the different species to select aphid populations of different sizes and distributions is likely to decrease interspecific competition.     

Population studies of Cheilosia fasciata (Diptera: Syrphidae), a leaf miner of Allium ursinum

Abstract.

• 1 Population dynamics of Cheilosia fasciata were described based on a sampling programme covering all developmental stages.
• 2 Failure to oviposit and mortality which was due to parasitization of pupae contributed most to total generation mortality.
• 3 Abundance of older larvae was regulated by density-dependent intraspecific competition for food.
• 4 These findings were reinforced by a field experiment which manipulated food levels and suggested that losses in numbers on ‘low food’ plots were in part compensated for by producing low-sized adults.

     

Baseline susceptibilities to imidacloprid for green apple aphid and spirea aphid (Homoptera: Aphididae) collected from apple in the Pacific northwest

Susceptibilities to the neonicotinyl insecticide imidacloprid were determined for clones of apple aphid, Aphis pomi De Geer, and spirea aphid, Aphis spiraecola Patch, collected from conventional and organic apple orchards and from crab apple and wild apple in Washington state and British Columbia over a period of 6 yr. For aphids collected during 1996--1998, adults were dipped in test solutions by using the Food and Agriculture Organization protocol, and third instars and adults were reared on treated apple leaf disks. During the final 3 yr of study, bioassays involved only third instars on treated leaf material. Tests showed that A. spiraecola was significantly more tolerant to imidacloprid compared with A. pomi. Depending on the bioassay method and aphid developmental stage, average LC50 values for A. spiraecola were 4.4 -5.7 times higher than those for A. pomi established under the same test conditions. Clones of both species from Washington were marginally more tolerant to imidacloprid than clones from British Columbia, but the differences were generally not significant. Average measures of susceptibility for clones from organic orchards or unsprayed trees also did not differ from those for clones from conventional orchards, and there was no evidence for increasing LC50 values over the 6 yr of study. Differences in susceptibility to insecticides between these two anatomically similar species should be considered during the testing of new products for use on apple.     

Survival and reproduction of Laricobius nigrinus Fender (Coleoptera: Derodontidae), a predator of hemlock woolly adelgid,Adelges tsugae Annand (Homoptera: Adelgidae) in field cages

Laricobius nigrinus Fender (Coleoptera: Derodontidae) is being evaluated as a biological control agent for the hemlock woolly adelgid (HWA), Adelges tsugae Annand (Homoptera: Adelgidae). Predator exclusion studies on survival, reproduction, and impact on HWA populations were investigated over two years in Virginia, US. In year 1, branches were selected to receive one of three treatments: caged hemlock branches with predators; caged hemlock branches without predators; and uncaged hemlock branches. L. nigrinus adults survived from February to April, producing up to 41 progeny per female. Adelgid densities on branches exposed to L. nigrinus exhibited a significantly higher rate of decline than those on branches not exposed to predators. Additionally, the final density of sistens and progrediens was significantly lower on caged branches containing L. nigrinus than on caged and uncaged branches without predators. In year 2, L. nigrinus survival and predation was evaluated over two 10-week sample periods: (November–January and February–April). L. nigrinus survived throughout the 6-month test period, with 89% surviving through January and 55% through April. Between February and April, 38 progeny were produced per beetle. The decrease in adelgids, measured in both numbers of adelgids and percent reduction per branch, was significantly higher (p < 0.0001) on caged branches with L. nigrinus than on those without predators.     

A meridic diet for the rearing of Hyaliodes vitripennis (Hemiptera: Miridae), a predator of mites in apple orchards

We compared biological parameters of the mite predator Hyaliodes vitripennis (Hemiptera: Miridae) reared on live Tetranychus urticae Koch versus two artificial diets used in rearing generalist predators: Coleomegilla maculata lengi Timberlake (Coleoptera: Coccinellidae) and Chrysoperla rufilabris Burmeister (Neuroptera: Chrysopidae). Both coccinellid and chrysopid diet resulted in lower mortality and increased longevity of H. vitripennis, but daily fecundity was greater with the former. The phagostimulant β-sistosterol had the greatest impact on H. vitripennis mortality (lowest) and nymphal weight gain (highest) when added to the coccinellid diet. These results demonstrate that H. vitripennis could be reared on an artificial diet, and suggests that β-sistosterol has phagostimulant properties for this predator.     

Responses of Episyrphus balteatus DeGeer (Diptera: Syrphidae) in relation to prey density and predator size

Laboratory experiments were conducted to determine the functional and numerical responses of the aphidophagous hover fly Episyrphus balteatus DeGeer (Diptera: Syrphidae) to different densities of 4th instar black bean aphids, Aphis fabae Scopoli (Homoptera: Aphididae), on broad bean, Vicia faba L. (Fabaceae). Two different-sized larvae of predators were tested in different densities of similar-sized prey to determine whether functional response parameters depended on the body sizes of predator and prey. In numerical response experiments, gravid E. balteatus females were exposed individually to different densities of 4th instars of A. fabae on cut sections of the broad bean plant, V. faba L. Logistic regression suggested a type II functional response for both larval sizes of E. balteatus. The searching efficiency (a) of the larger larvae was higher than that of the smaller ones. Prey consumption was higher, and handling time (T_h) was lower for larger larvae than smaller ones. The theoretical maximum number of A. fabae nymphs eaten by the different-sized larvae was 125 and 269 nymphs per day. Larger E. balteatus larvae are more efficient predators for aphid management strategies. The reproductive numerical response, in terms of the number of eggs laid, increased curvilinearly with increasing prey density, but the proportion of eggs laid (egg number/prey density) decreased as the initial density of prey increased.     

Effect of trap color and orientation on the capture of Aphelinus mali (Hymenoptera: Aphelinidae), a parasitoid of woolly apple aphid (Hemiptera: Aphididae)

The factors affecting trap capture of adult Aphelinus mali (Haldeman) (Hymenoptera: Aphelinidae) were studied in 2010-2011 in eastern Washington apple (Malus spp.) orchards infested with its host woolly apple aphid, Eriosoma lanigerum (Hausmann) (Hemiptera: Aphididae). The initial study of white sticky cards indicated that traps stapled to the trunk in a vertical orientation had the highest capture. A factorial experiment of three colors (clear, white, and yellow) by three orientations (trunk, scaffold, and hanging) indicated that yellow traps and traps on trunks caught higher numbers ofA. mali. For this reason, the recommended trap for this natural enemy is a yellow trap stapled to the trunk. Having a readily available and effective sampling method for this species may be helpful in implementing biological control programs and assessing the impact of different spray regimes.     

Feeding preference of three lady beetle predators of the hemlock woolly adelgid (Homoptera: Adelgidae)

In a laboratory study, we tested the feeding preferences of three coccinellid predators of hemlock woolly adelgid, Adelges tsugae Annand, an introduced pest of hemlock in the eastern United States. The species tested were Sasajiscymnus tsugae Sasaji & McClure (formerly Pseudoscymnus tsugae) from Japan, Scymnus ningshanensis Yu & Yao from China, and Harmonia axyridis (Pallas), a generalist species introduced from Asia that is currently widespread in eastern hemlock, Tsuga canadensis Carriere, forests. We measured the feeding preference of each beetle species when given the choice of A. tsugae and either 1) Pineus strobi (Hartig) on Pinus strobus L.; 2) Adelges laricis Vallot on Larix decidua Mill.; 3) Adelges cooleyi (Gillette) on Pseudotsuga menziesii (Mirb.) Franco; or 3) Paraprociphilus tessellatus (Fitch) on Alnus serrulata (Ait.) Willd. We evaluated beetle preference for adults, nymphs, and eggs of each prey species. Generally, when adult or nymphal prey stages were compared, S. tsugae preferred A. tsugae adults to P. strobi, A. cooleyi, A. laricis, and P. tessellatus. S. ningshanensis showed less preference between adelgid species, but it did not prefer P. tessellatus nymphs. When preferences for adelgid eggs were assayed, S. tsugae and S. ningshanensis showed no preference between A. tsugae and A. cooleyi or P. strobi, but S. tsugae did prefer A. tsugae to A. laricis. Larvae of S. tsugae were unable to survive on P. tessellatus nymphs. H. axyridis adults readily consumed both A. tsugae and P. tessellatus, but H. axyridis larvae did not complete their life cycle on A. tsugae. Our host range tests suggest that S. ningshanensis and S. tsugae may feed on several species of Adelgidae and that A. tsugae is often preferred.     

Feeding History Affects Intraguild Interactions between Harmonia axyridis (Coleoptera: Coccinellidae) and Episyrphus balteatus (Diptera: Syrphidae)

While the effect of several factors such as predator and prey size, morphology and developmental stage on intraguild predation (IGP) is widely investigated, little is known about the influence of diet on the occurrence and outcome of IGP. In the present study, the effect of the diet experienced during larval development on IGP between the ladybird Harmonia axyridis and the syrphid Episyrphus balteatus is investigated. Four diets were tested for H. axyridis: eggs of the Mediterranean flour moth Ephestia kuehniella, pea aphids, Acyrthosiphon pisum, in an ad libitum amount, pea aphids in a limited amount, and honey bee pollen. For E. balteatus only the two aphid diets were tested. First, experiments were performed to determine the quality of the various diets for development of both predators. Second, IGP experiments between H. axyridis and E. balteatus were performed both in Petri dishes and on potted pepper plants. The diet of both species influenced the incidence of IGP between H. axyridis and E. balteatus both in Petri dishes and on potted plants. In general, smaller larvae of H. axyridis (those fed on poor or restricted diet) fed more on hoverflies than large (well-nourished) ladybird larvae. Further, poorly nourished (smaller) larvae of E. balteatus were more susceptible to predation than well-fed (larger) hoverfly larvae. The observed effects were not only due to the lower fitness of larvae of both predators reared on an inferior quality diet but also to changes in predator behaviour. The results from this study show that IGP interactions are influenced by a multitude of factors, including feeding history of the organisms involved, and emphasize the importance of taking these factors into account in order to fully understand the ecological relevance of IGP.     

Isolation and characterization of microsatellite loci from the woolly apple aphid Eriosoma lanigerum (Hemiptera: Aphididae: Eriosomatinae)

Eight novel microsatellite primer pairs are presented for Eriosoma lanigerum, representing the first microsatellite markers available for this genus. Loci were characterized for 27 individuals from one single orchard in Central Chile. All loci were polymorphic within E. lanigerum (three to 11 alleles per locus; observed heterozygosity ranging from 0.41 to 0.93), and are therefore useful for population genetic studies within the species.     

Assessment of aphid colonies by hoverflies. III Pea aphids andEpisyrphus balteatus (de Geer) (Diptera: Syrphidae)

The syrphid flyEpisyrphus balteatus (de Geer) migrating from maple trees to leguminous plants in mid-April, assesses the qualitative and quantitative value of pea aphid colonies for securing successful development of her offspring. She selects young and “promising” pea aphid colonies of small size. This generally agrees with the “buy-futures” ovipositional tactic the syrphid fly adopts when it utilizes the maple aphids. The advantage of a “buy-futures” ovipositional tactic found in many syrphid species is discussed in comparison with other aphidophagous insects.     

Assessment of aphid colonies by hoverflies. I maple aphids andEpisyrphus balteatus (de Geer) (Diptera: Syrphidae)

In the syrphid hoverflyEpisyrphus balteatus (de Geer), females in search of oviposition sites are assessing the qualitative and quantitative value of aphid colonies for securing the successful development of their offspring. They select small, young and “promising” aphid colonies consisting of nymphs and/or fundatrices as their oviposition sites, and neglect large, older ones including winged adults. Such “buy-futures” tactics will benefit the offspring in finding suitable and sufficient food.     

On the distribution of Temnostoma vespiforme (Diptera, Syrphidae) in North America

The occurrence of Temnostoma vespiforme (L.) in the Holarctic Region is questioned. The North American specimens previously determined as T. vespiforme (L.) are re-examined. Their differences from the European specimens in the body coloration and in the morphology of the male and female genitalia are listed.