Syrphid Predators Research Articles

Feeding and egg distribution studies of Heringia calcarata (Diptera: Syrphidae), a specialized predator of woolly apple aphid (Homoptera: Eriosomatidae) in Virginia apple orchards.

Predation by the aphidophagous syrphid fly Heringia calcarata (Loew) on woolly apple aphid, Eriosoma lanigerum (Hausmann), was studied in the laboratory and in Virginia apple orchards. Feeding studies compared the prey suitability of three temporally sympatric aphid pests of apple: spirea aphid, Aphis spiraecola Patch; rosy apple aphid, Dysaphis plantaginea (Passerini); and woolly apple aphid. Significantly more H. calcarata larvae survived and completed development on a pure diet of woolly apple aphid than on rosy apple aphid, and none survived on spirea aphid. Final larval weights were significantly greater, and the larval developmental period was significantly shorter on woolly apple aphid than on rosy apple aphid, but neither the duration of pupal development nor adult weight differed between diets. H. calcarata larvae consumed an average of 105 woolly apple aphids during their development. Naïve, neonate larvae given access to all possible pair combinations of woolly apple aphid, rosy apple aphid, and spirea aphid consumed significantly more woolly apple aphids in all pairings that included woolly apple aphid. When given a choice of rosy apple aphid and spirea aphid, significantly more rosy apple aphids were consumed. Weekly counts of syrphid eggs found in woolly apple aphid, rosy apple aphid, and spirea aphid colonies collected from apple trees showed that two generalist hover fly predators, Eupeodes americanus (Wiedemann) and Syrphus rectus Osten Sacken, were present in colonies of all three aphid species and that E. americanus was the most abundant syrphid predator in A. spiraecola and D. plantaginea colonies. H. calcarata eggs were found only in woolly apple aphid colonies and were more abundant there than E. americanus and S. rectus. These data suggest that H. calcarata is a specialized predator of woolly apple aphid in the apple ecosystem in Virginia.

Larval interactions in aphidophagous predators: effectiveness of wax cover as defence shield of Scymnus larvae against predation from syrphids

AbstractSmall‐sized predators in the aphidophagous guild of Aphis gossypii Glover colonies on hibiscus trees in Japan exploit aphids at low prey abundance. Scymnus (Pullus) posticalis Sicard beetles were the first predatory species to attack aphids in the spring, and their larvae co‐occurred with larvae of Eupeodes freguens (Matsumura) syrphids in aphid‐infested leaves of hibiscus for 3 weeks in absence of large‐sized coccinellid predators. Larval interaction between Scymnus and syrphid predators was examined in relation to effectiveness of wax cover of Scymnus against predation from syrphids. Waxless first instar larvae were not protected but wax‐covered larvae of second, third and fourth instars were protected from predation by syrphid larvae. The protection was lower in the second instar which has a thin wax cover and significantly higher in the third and fourth instars having a thick wax cover. In addition, larvae from which the wax was removed were significantly more vulnerable to predation. Vulnerability of Scymnus larvae to predation from syrphids was directly related to the thickness of wax cover. Results suggest that the wax cover of Scymnus larvae act as an effective defence mechanism against predation from syrphid larvae.

Impact of Syrphid Predation on Production of Migrants in Colonies of the Brown Citrus Aphid, Toxoptera citricida (Homoptera: Aphididae)

Abstract Colonies of the brown citrus aphid, Toxoptera citricida (Kirkaldy), were studied in the laboratory with and without larval predation by the syrphid Pseudodorus clavatus (F.). Syrphid larvae fed for a mean of 8 days and the size of aphid colonies was significantly reduced compared to controls at day 4 after onset of feeding to day 9 inclusively. Colonies that survived predation by syrphid larvae grew to be as large as control colonies. Control colonies matured alatae earlier than did colonies subjected to actual or simulated predation. Significantly more reproductive apterae emigrated from control colonies than from those in the actual and simulated predation treatments and the emigration occurred significantly earlier. The lack of differences between paired T. citricida colonies in the actual and simulated predation treatments suggests that the only measurable effect of syrphid predation on aphid colonies was density reduction. There was substantial variation in aphid colony success (=production of migrants) within treatments. Both apterous and alate nymphs often failed to mature and late-maturing apterae failed to reproduce or emigrate. The results indicate that colonies of T. citricida that experience predation, whether real or simulated, suffer a delay in the production of alatae and produce fewer apterous migrants than colonies that escape predation.

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

Summary 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 6.0d̀C and 7.1d̀C 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 6.8d̀C) in combination with the required value from adult emergence to first oviposition, suggests a total requirement of approximately 374 DD above 6.8d̀C 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.

Crude aqueous‐extract (kairomone) from Aphis fabae Scop. (Hom., Aphidae) and its effect on the behaviour of the predator Metasyrphus corollae Fabr. (Dipt., Syrphidae) female

Abstract: Female Metasyrphus corollae Fabr., a syrphid predator on the bean aphid Aphis fabae Scop., responded to aqueous extract containing kairomones of the prey. The crude aphid‐extract was topically dropped onto clean leaves of Vicia faba. After application of aqueous‐extract at different aphid densities on the clean leaves, the predator showed variations in oviposition and searching behaviours in comparison with untreated leaves (control). The variations are summarized as follows: (1) the aqueous‐extract of aphids stimulate M. corollae females to lay eggs at all aphid densities. The number of eggs were directly proportional with aphid concentrations; (2) the predator M. corrolae female intensified its searching behaviour by increasing the total path length walked; (3) the number of turns exhibited is significantly higher as compared with those of control; and (4) the retention time spent by M. corollae females with treated plant is much more than that with clean plant at all aphid densities. The present results showed that the aphid aqueous‐extract contains the active ingredients (kairomones) which induce a considerable change in the searching pattern and increase the oviposition rate of the predator syrphid females.

Life Table Studies on Eupeodes corollae (Fabricius) (Diptera:Syrphidae), a Predator of the Cabbage Aphid, Brevicoryne brassicae (Linnaeus) (Homoptera:Aphididae)

Life table studies on Eupeodes corollae (Fabricius), an important syrphid predator of the cabbage aphid, Brevicoryne brassicae (Linnaeus) in the mid-hill region of Himachal Pradesh revealed that the net reproductive rate (Ro) of the species was 187.52 female eggs/female. The true intrinsic rate of natural increase (r m ) was 0.134. The population multiplied 1.14 times per day during the generation and was able to multiply 2.55 times every week. On reaching a stable age-distribution, the population comprised approximately 97 per cent of immature stages.

The effects of natural enemies, competition, and host plant water availability on an aphid population.

I used a factorial experiment repeated in two years to assess the relative effects of natural enemy attack, interspecific competition, and water availability to the host plant, and of interactions among these factors, on the population dynamics of the aphid Aphis varians feeding on fireweed (Epilobium angustifolium). The impact of a suite of coccinellid and syrphid predators emerged as the predominant factor affecting the success of aphid colonies: colonies protected from natural enemies grew in size at a rate of ten percent per day, were only one tenth as likely to go extinct, and produced over ten times more dispersing alates. In contrast, I found only minor effects of removing flea beetles, the most abundant herbivore with which A. varians colonies cohabit fireweed stems, and of supplementing water availability to fireweed host plants, in spite of a significant effect of watering frequency on aphid growth in the green-house. There was no evidence of significant two- or three-way interactions among factors. Hence, despite the potential complexity of the food web in which it is embedded, the dynamics of A. varians appears to be driven predominantly by a single factor, i.e. interactions with natural enemies.

Thermal requirements for development of aphidophagous Coccinellidae (Coleoptera), Chrysopidae, Hemerobiidae (Neuroptera), and Syrphidae (Diptera): some general trends.

The sum of effective temperatures (SET) and lower development threshold (LDT) were established for eggs and/or pupae of central European populations of 20 species of chrysopid, coccinellid, hemerobiid, and syrphid predators of aphids. LDT ranged between 5.6° and 12.2°C, SET between 38.3 and 140.9 day degrees (dd), with broad overlap among stages and taxa. When LDT was plotted against SET, the data for both eggs and pupae were scattered along a single regression line which predicted a 0.47°C decrease in LDT per 10 dd increase in SET (r=-0.77, p<0.001). A regression calculated from published data from all over the world predicted a 0.24°C/10 dd decrease in LDT, and the data were more scattered (r=-0.38, p<0.01). This is perhaps the first report on the functional relationship between LDT and SET at the interspecific level. The species and stages differed in typical development length (VDL) and in the extent of its deceleration by low temperatures (DD). DD increased with increasing VDL, but the relative effect of low temperature on development length (DD/VDL ratio) reflected thermal adaptations consistent with the life history of the species. Polyvoltine species were less affected by low temperatures than monovoltine species, particularly the thermophilic ones.

POPULATION DYNAMICS OF THE CABBAGE APHID, BREVICORYNE BRASSICAE (HOMOPTERA: APHIDIDAE) AT VANCOUVER, BRITISH COLUMBIA: V. A SIMULATION MODEL

AbstractA computer model was written to simulate the population dynamics of the cabbage aphid, Brevicoryne brassicae (L.), on the host Maris Kestrel kale, Brassica oleracea L., at Vancouver, British Columbia. The model incorporated the effects of temperature, morph determination, plant quality, predators, parasites, and leaf fall. Comparisons of simulated results with field observations indicated that although B. brassicae, Aphidoletes aphidimyza (Rond.), and Diaeretiella rapae (M'Intosh) were reasonably well understood, syrphid predation was not, and appropriate feed-back mechanisms which could prevent monotonic increase or decrease in the simulated population were lacking. A detailed study in which the population dynamics of the prey is accounted for in terms of the numerical and functional responses of syrphid predators is necessary to understand the population dynamics of B. brassicae on Maris Kestrel kale at Vancouver. Comparisons with other aphid systems suggest that a major change in one component of the system can be compensated for by changes in other components. An overview of the cabbage aphid system at Vancouver is given.

Natural Mortality Factors Acting on Potato Aphid (Macrosiphum euphorbiae) Populations in Processing-Tomato Fields in Ohio

The populations of potato aphids and their natural enemies on processing-tomatoes were monitored in 1980 and 1981 in Wooster and Fremont, Ohio. Rainfall in combination with high winds appeared to be the major factor in mortality in 1980. In the dry 1981 season, large populations developed. Natural enemies did not control aphid populations in Wooster in 1981, or in either location in 1980. Aphidius nigripes was the dominant parasitoid, but its effectiveness against aphids was limited by high hyperparasitization by Asaphes lucens and other hyperparasitoids. Predators (coccinellids, neuropterans, and syrphids) exhibited slow numerical responses and were for the most part ineffective in controlling aphid populations. High population levels in Wooster in 1981 caused massive emigration of alates. In Fremont in 1981, the population levels were much lower. Slower aphid colonization, syrphid predation early in the season, and density-dependent parasitization throughout the season appeared to have been responsible for the lower aphid population in Fremont. Large numbers of natural enemies apparently immigrated to the Fremont site from a heavily infested, adjacent tomato field.

Population studies ofBrevicoryne brassicae(L.), its parasites and hyperparasites in England

SummaryStudies on populations ofBrevicoryne brassicae(L.), its parasites and hyperparasites were carried out by actual counting in the sprouts field and by sticky and water traps.B. brassicaewas found to be attacked by one primary parasite,Diaretiella rapae(McIntosh), which in turn is parasitized byAlloxysta brassicae(Ashm.),Asaphes vulgarisWalker,A. suspensus(Nees),Pachyneuron minutissimum(Förster) andDendrocerus carpenterii(Curtis). The aphid population in the field was started by immigrant alates which were found flying too early to be synchronized with the sprouts plants. SimilarlyD. rapaewas not synchronized with the aphids although many individuals could have been carried into a plot through parasitized immigrant alates, of which less than 30% were found parasitized. Because of high hyperparasitism (especially byA. brassicae)D. rapaewas not able to maintain a high rate of parasitism to curb the aphid population growth. The maximum percentage mummies being 27.8%, while the maximum, percentage parasitism being 56.6% recorded only during the early 1974 season (mean=12.9%). The decline of aphid population from September onwards was largely due to the cold weather, Syrphid predation and occasionally fungal attack. The high rate of hyperparasitism byA. brassicaeis attributed to its better synchronization withD. rapae. The mean percentage of parasite that emerged from mummies collected during 1973–74 wereD. rapae31.3%,A. brassicae64.3%,A. vulgarisandA. suspensus4.3%,D. carpenterii0.2% andP. minutissimum0.1%.

Natural enemies of Toxoptera aurantii (Boy.) (Homoptera: Aphididae) on cocoa in Ghana

Natural enemies of the black citrus aphid, Toxoptera aurantii (Boy.), on cocoa in Ghana are identified. Biology of some of the natural enemies is followed. Behaviour of the coccinellid and syrphid predators is studied in detail. Effectiveness of the predators in reducing the aphid populations is discussed.

Spring Populations of the Green Peach Aphid 1 on Peach Trees and the Role of Natural Enemies in Their Control 23

A 2-year study of the spring population of Myzus persicae (Sulzer) on peach trees showed that the number of surviving fundatrices reaching reproductive maturity represented less than 2% of the overwintering eggs. Colonies established from surviving fundatrices protected from natural enemies by slecve cages displayed a tremendous numerical recovery. For example, in a protected environment (cage) the average number of alate aphids per stem mother was 3596 in 1970, and 1080 in 1971. In contrast, on unprotected twigs the natural enemies, primarily coccinellid and syrphid predators, played a major role in reducing the production of alate aphids by an estimated 95% in both years (based on counts of immature aphids).

Hedges. VI. Habitat Diversity and Crop Pests: A Study of Brevicoryne brassicae and its Syrphid Predators

Hedges. VI. Habitat Diversity and Crop Pests: A Study of Brevicoryne brassicae and its Syrphid Predators

Oviposition Responses by Aphidophagous Syrphidae (Diptera)

CURRENT work on syrphid predators of aphids has demonstrated some behavioural responses of the ovipositing adult females which may be significant in relation to a general understanding of natural enemy action and also to the better use of natural enemies in the control of insect pests.