Host quality of different aphid species for rearing Diaeretiella rapae (McIntosh) (Hymenoptera: Braconidae)

This study aimed to evaluate the quality of the aphid Myzus persicae (Sulzer), Lipaphis erysimi (Kaltenbach) and Brevicoryne brassicae (L.) as hosts for the parasitoid Diaeretiella rapae (McIntosh). Parasitization by D. rapae was higher on M. persicae than on L. erysimi and B. brassicae. The time of development of D. rapae from egg to mummy or egg to adult male or female were shorter on M. persicae than on L. erysimi and B. brassicae. Moreover, D. rapae showed no significant differences in the emergence rate, sex ratio and longevity when reared on the three aphid species. Myzus persicae was the largest aphid host, with B. brassicae and L. erysimi being of intermediate and of small size, respectively. Diaeretiella rapae reared on M. persicae was larger than when reared on L. erysimi and B. brassicae, and females of D. rapae were significantly larger than males on M. persicae, but males of D. rapae were larger than females when reared on L. erysimi. No difference in size was detected between males and females in parasitoids reared on B. brassicae. Among the aphid species studied, M. persicae was found to be the most suitable to D. rapae.     

Tritrophic interactions between cabbage cultivars with different resistance and fertilizer levels,cruciferous aphids and parasitoids under field conditions

Tritrophic interactions involving cabbage Brassica oleracea var. capitata cultivars +/- fertilizer, Brevicoryne brassicae (Linnaeus) and Myzus persicae (Sulzer), and the parasitoids Diaeretiella rapae (M'cIntosh) and Aphidius sp. were conducted in 1998 and 1999. Brevicorne brassicae was the dominant aphid species on all cultivars +/- fertilizer, except for some treatments in late season 1998. Ruby Ball (red-leaved with antixenosis factors for B. brassicae alates) +/- fertilizer was consistently less colonized by aphids in early stages of plant growth, although only significantly so compared with Derby Day (green-leaved, susceptible to aphids) without fertilizer for B. brassicae and Minicole (green-leaved with antibiosis factors for B. brassicae) with fertilizer for M. persicae. In early 1999, only B. brassicae was present and no significant differences between cultivars were seen. In the mid to late season 1998, the highest aphid infestations were usually found on Derby Day, although only significantly so for B. brassicae, in some treatments. In 1999, higher aphid infestations were observed on Derby Day in mid to late season and some significant differences were found for M. persicae as well as for B. brassicae. In both years, Ruby Ball had the greatest mummy:aphid ratios early season, with no consistent difference between the other cultivars. Later in the season, mummy:aphid ratios were generally highest on Minicole. Parasitism differed in seasonal occurrence and relative abundance. Diaeretiella rapae mummies were found earlier than Aphidius sp. There was evidence of a beneficial interaction between the degree of plant resistance and biological control in early to mid season.     

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.     

Effect of cabbage cultivars with varying levels of resistance to aphids on the performance of the parasitoid,Aphidius colemani (Hymenoptera: Braconidae)

The effect of aphid resistance in plant cultivars on parasitism of Myzus persicae (Sulzer) and Brevicoryne brassicae (Linnaeus) by Aphidius colemani Viereck was investigated under laboratory conditions using three cultivars of common cabbage, Brassica oleracea var. capitata. Significantly greater aphid populations were found on cv. Derby Day (green-leaved, susceptible to both aphid species), regardless of the presence or absence of parasitoids, compared with cv. Minicole (green-leaved, partially resistant with antibiosis factors for B. brassicae) or cv. Ruby Ball (red-leaved, partially resistant with antixenosis factors for B. brassicae). Minicole had the greatest proportion of parasitized aphids and Derby Day the least. A significantly lower percentage of emerged parasitoids were recorded on Minicole for both aphid species compared with Derby Day and Ruby Ball. The implication of the results are discussed in relation to the integrated control of aphids.     

An analysis of the deterrent effect of aphids on cabbage root fly (Delia radicum) egg-laying

Abstract. 1. The cabbage root fly, Delia radicum (L.), was deterred from laying eggs on brassica plants with >250 cabbage aphid, Brevicoryne brassicae (L.), or peach-potato aphid, Myzuspersicae (Sulz.).
2. Flies did not lay on plants infested with >250 aphids.
3. Preparations of (E)-β-farnesene, the aphid alarm pheromone, deterred the flies from laying only at the extremely high dose of 32 mg/plant.
4. Although M. persicae secreted large (1 ng/insect) amounts of alarm pheromone and B. brassicae extremely small (<0.01 ng/insect) amounts, both aphids equally deterred D. radicum from laying.
5. The deterrent effect appeared to result from the aphids physically disturbing the flies during host-plant selection.     

INFECTIVITY OF APHIDS BRED ON VIRUS-INFECTED CAULIFLOWER PLANTS

Caged cauliflower plants infected with either cabbage black ring spot virus (CBRSV) or cauliflower mosaic virus (CIMV) were colonized with Myzus persicae or Brevicoryne brassicae. Winged and wingless aphids that voluntarily flew or walked from these plants were transferred singly to healthy cauliflower or other brassica seedlings to compare their feeding behaviour and ability to transmit the viruses. Wingless aphids settled to probe more readily than winged, and B. brassicae was initially more restless than M. persicae. CIMV was more readily transmitted than CBRSV by both species, and B. brassicae rarely transmitted CBRSV. Wingless aphids transmitted less often than winged ones, and no wingless B. brassicae transmitted CBRSV, although they did CIMV. Fewer aphids transmitted CBRSV from old plants than from young ones, but plant age had little effect on CIMV transmission.     

The effect of leaf excision on the performance of Myzus persicae and Brevicoryne brassicae in relation to the nutrient treatment of the plants

Two groups of brussels sprout plants of one variety given different fertilizer treatments proved ‘resistant’ and ‘susceptible’ to both Myzus persicae and Breicoryrie brassicae, as measured by aphid mean relative growth rate. The hypothesis that leaf disc would fail to reflect differences in ‘nutritionallybased’ plant resistance was confirmed with B.brussicue but not M.persicae. Both aphids grew more slowly on discs than leaves of ‘susceptible’ plants; the reverse tendency showed on ‘resistant’ material. Total:(, amino nitrogen proved poorly correlated with aphid performance. Previously published (van Emden & Bashford, 1971) equations relating individual amino acids to aphid performance gave a better fit to the results, but still failed to account for the reduced performance of the aphids on ‘susceptible’ discs.     

Some host-plant factors affecting oviposition by aphidophagous Syrphidae (Diptera)

Although most aphidophagous syrphid species lay their eggs close to aphids, Platycheirus peltatus (Meig.), Melanostoma scalare (F.) and M. mellinum (L.) laid freely on uninfested brussels sprout plants. The existence of species that will lay in the absence of aphids may be valuable in biological control and also provides a useful tool for the investigation of non-aphid oviposition stimuli. Plant species and plant appearance were both important factors in P. peltatus oviposition. Particular sites on the plant were chosen for oviposition by Syrphus balteatus (Deg.). The nature of the substrate at the oviposition site affected the size of the egg batches laid there by M. scalare, M. mellinum, P. peltatus and P. clypeatus (Meig.). The possibility is discussed that plant-location is the older-established system of host-finding and that an aphid-location system has gradually superseded it during the evolution of the obligatorily aphidophagous Syrphinae.     

十种蚜虫的生化鉴别（同翅目：蚜总科）

用聚丙烯酰胺等电聚焦凝胶电泳分析了棉蚜、甘蓝蚜、洋槐蚜、桃蚜、柳二尾蚜、茜草蚜、绣线菊蚜、艾蚜、夹竹桃蚜和月季长管蚜等十个蚜种的酯酶同工酶。除月季长管蚜的酶活很低外,另９个蚜种都有自己特有的酶谱,彼此易于区分。桃蚜和柳二尾蚜的酯酶是多态性的。     

HOST FINDING BY APHIDS IN THE FIELD: APHIS FABAE SCOP. (GYNOPARAE) AND BREVICORYNE BRASSICAE L.; WITH A RE-APPRAISAL OF THE ROLE OF HOST-FINDING BEHAVIOUR IN VIRUS SPREAD

Aphis fabae gynoparae occurred in the same large proportion in simultaneous collections of all aphids alighting and probing on, and taking off from, a host plant (spindle) and a non-host (peach), and behaved similarly when approaching and leaving them in the same conditions. Most alighters took off again from leaves of both kinds within a few minutes, staying longer and probing more times on the host. In atmospheric conditions favouring local 'hovering' instead of dispersal, flying and alighting aphids became concentrated around host plants, not through any specific attraction to them, but apparently because more aphids had accumulated upon them and were now taking off.
Brevicoryne brassicae occurred in the same large proportion in simultaneous collections of aphids alighting on a host plant (cabbage) and a non-host (sugar beet). No satisfactory evidence was found of preferential alightment on cabbage and there were indications of preferential alightment on the non-host. A very small minority of the A. fabae and B. brassicae that alighted on their hosts stayed there long enough to larviposit. This minority was rather larger among alighters late in the day, but in the absolute sense, more colonization occurred during earlier periods when more aphids arrived.
The intensely dispersive type of host-finding behaviour in Myzus persicae, A. fabae and B. brassicae may be common among Aphididae. It seems ideal for the dissemination of non-persistent plant viruses, more particularly among the less-favoured host plants of each aphid. The tendency to commensal association between virus and vector provides an ecological framework which may govern the incidence of virus-vector specificity and symbiosis.     

Resistance to attack by Brevicoryne brassicae among plants of Brussels sprouts

Because they remained almost uncolonized by the cabbage aphid (Brevicoryne brassicae (L.)) throughout the growing season, plants of Brussels sprouts were singled out in each of 4 years, from plots heavily infested with the aphid, as possibly being resistant to attack. Clones of these plants were established from cuttings and tested in a controlled environment by inoculation with B. brassicae and later, in the field, by natural infestation. The tests confirmed that some of the plants were resistant to the aphid, and the most resistant of those from the first year of the work proved at least as resistant as any subsequently found. The resistance was expressed as antibiosis, but in the field host non-preference was also shown by incoming winged aphids. The possibility that biotypes of B. brassicae might exist, to which the resistant sprout clones were not necessarily resistant, was investigated using B. brassicae collected from sprouts from each of several areas in England. Eight sprout clones, seven of which were known to be resistant, and the other susceptible, to B. brassicae from Wellesbourne were tested with these other B. brassicae. The results showed that biotypes of the aphid, with differing abilities to colonize respective sprout clones, existed in each area, and of the seven sprout clones resistant to the Wellesbourne aphid, only one appeared never to be fully susceptible to one or more of the other biotypes of B. brassicae.     

Relative feeding rates of Brevicoryne brassicae and Myzus persicae on Brussels sprout plants in relation to their susceptibility to systemic insecticides

Brevicoryne brassicae and Myzus persicae removed similar quantities of ³²P-labelled material from Brussels sprout leaves whether they fed for 24 or 48 h periods. They also removed similar quantities from untreated leaf disks as from leaf disks treated with a sub-lethal dose of menazon. When a lethal dose was used, the uptake of ³²P by B. brassicae was significantly less than by M. persicae. M. persicae excreted a greater proportion of ³²P label in the honeydew than B. brassicae and a greater proportion of the amount absorbed was lost in the progeny of this aphid than in B. brassicae.
B. brassicae was 6.2 times more susceptible than M. persicae to dimethoate acting systemically. When it was applied topically the aphids were equally susceptible.
Considerable variation in uptake of ³²P occurred between replicates and the factors that could influence this are discussed.     

Host-related fitness trade-offs in a presumed generalist parasitoid, Diaeretiella rapae (Hymenoptera: Aphidiidae)

Abstract.  1. Host ranges of parasitoid wasps are mediated by behavioural responses to hosts and their environment (infectivity), and development in hosts (virulence). Determinants of host range were measured in Diaeretiella rapae (Hymenoptera: Aphidiidae), which has been described as a generalist that attacks more than 60 species.
2. In northern Colorado, this wasp mainly attacks two hosts: cabbage aphid ( Brevicoryne brassicae ) and Russian wheat aphid ( Diuraphis noxia ). Here, laboratory experiments are described in which D. rapae originating from these two hosts were offered several hosts for oviposition. Both infectivity and virulence were measured.
3. Infectivity included host acceptance and handling time, while virulence was measured as productivity (number of progeny), survival of immatures within hosts, development time, and sex ratio.
4. Wasps had higher productivity and survival when attacking 'home' hosts than 'alternate' hosts, and trade-offs were found by quantitative genetic analyses to be genetically determined. Sex ratio and development times also showed trade-offs, but mainly related to the host environment in which females were reared.
5. In previous genetic studies in northern Colorado, populations were genetically subdivided on the scale of 1 km. The fitness differences described here could be strong enough to create populations adapted to different hosts, but it appears that gene flow is sufficient to prevent formation of separate lineages on the two hosts.
6. Rather than being a generalist with a broad host range, D. rapae is a serial specialist, attacking particular hosts according to availability in different seasons or in different geographical areas.     

芥子油苷在甘蓝蚜寄主部位选择行为中的作用

利用刺吸电位技术（EPG）记录甘蓝蚜Brevicoryne brassicae在芥菜Sinapis alba 不同部位上的取食行为,同时用高压液相色谱（HPLC）分析芥菜相应部位的芥子油苷(glucosinolates)含量,据此分析芥子油苷在甘蓝蚜对寄主部位偏好行为中的作用。选择芥菜三个部位进行取食行为记录和化学分析,即新出完全叶(第7片)的叶片、叶柄,以及花茎。相对于其它两个部位,甘蓝蚜的口针在花茎上用较少的刺探次数和较短的时间到达韧皮部;一旦口针进入韧皮部持续吸食阶段,蚜虫在三个部位的取食行为没有太大的差异。只在花茎的表皮和皮层中测定到较高含量的白芥子苷（glucosinalbin）。因此,本实验的结果证明,白芥子苷是甘蓝蚜寄主部位选择的关键信号化学物质或取食促进剂。     

Some factors influencing the occurrence and site of oviposition by aphidophagous Syrphidae (Diptera)

Syrphids were not deterred from ovipositing on suitable plants by the presence of other syrphid eggs, larvae or larval gut contents. Heavy infestations of Aphis fabae Scop, on bean plants (Viciafaba L.) induced Platycheirus manicatus (Meig.) to lay preferentially on neighbouring uninfested plants. Such behaviour was not found for Syrphus species. Nor did flowers, a source of adult food, stimulate oviposition nearby. The site of oviposition in relation to Brevicoryne brassicae L. on brussels sprouts (Brassicae oleracea gemnifera L.) varied markedly according to species: in similar conditions Syrphus luniger Meig. laid over 50% of its eggs touching aphids and less than 1% on uninfested plants, whereas P. manicatus laid less than 5% touching aphids and over 50% on uninfested plants. Most eggs were laid close to the edge of the leaf, especially by Platycheirus species, e.g. P. scutatus Meig. which laid over 90% within 5 mm of the edge of the leaf.     

Development of the parasitoid,Cotesia rubecula (Hymenoptera: Braconidae) in Pieris rapae and Pieris brassicae (Lepidoptera: Pieridae): evidence for host regulation

Several recent models examining the developmental strategies of parasitoids attacking hosts which continue feeding and growing after parasitism (=koinobiont parasitoids) assume that host quality is a non-linear function of host size at oviposition. We tested this assumption by comparing the growth and development of males of the solitary koinobiont endoparasitoid, Cotesia rubecula, in first (L1) to third (L3) larval instars of its preferred host, Pieris rapae and in a less preferred host, Pieris brassicae. Beginning 3 days after parasitism, hosts were dissected daily, and both host and parasitoid dry mass was determined. Using data on parasitoid dry mass, we measured the mean relative growth rate of C. rubecula, and compared the trajectories of larval growth of the parasitoid during the larval and pupal stages using non-linear equations. Parasitoids generally survived better, completed development faster, and grew larger in earlier than in later instars of both host species, and adult wasps emerging from P. rapae were significantly larger than wasps emerging from all corresponding instars of P. brassicae. During their early larval stages, parasitoids grew most slowly in L1 P. rapae, whereas in all other host classes of both host species growth to pupation proceeded fairly uniformly. The growth of both host species was markedly reduced after parasitism compared with controls, with the development of P. brassicae arrested at an earlier stage, and at a smaller body mass, than P. rapae. Our results suggest that C. rubecula regulates certain biochemical processes more effectively in P. rapae than in P. brassicae, in accordance with its own nutritional and physiological requirements. Furthermore, we propose that, for parasitoids such as C. rubecula, which do not consume all host tissues prior to pupation, that parasitoid size and host quality may vary independently of host size at oviposition and at larval parasitoid egression.     

Differences in susceptibility to attack by Brevicoryne brassicae (L.) on brussels sprouts

The attack by alate and other forms of Brevicoryne brassicae (L.) and the amount of leaf malformation they caused on each of eighteen varieties or plant breeders' lines of brussels sprout were assessed in both 1967 and 1968 over the first 6 weeks following planting out. The results of the two years agreed closely despite differences in the dates of planting relative to aphid immigration. As a group, the Dutch varieties Roodnerf, Gravendeel, Tribune, Hercules and Castricum Glory were preferred by the incoming alates but suffered less damage than the least preferred inbred line, 3BL, of Cambridge No. 3. Some evidence of antibiosis was obtained, especially from a later experiment with three Cambridge inbred lines. However, in 1969 when there was a high rate of aphid multiplication on six varieties representing sprout types from Holland, Cambridge, Bedford and Ireland, any expression of host non-preference or antibiosis was soon obscured by the development of large aphid infestations and much damage. Under these circumstances, considerable varietal differences in tolerance to attack were found. Irish Elegance sustained most damage yet its most heavily attacked plants supported little more than half of the aphid numbers of equivalent plants of the most tolerant variety Darkmar 21. The Dutch varieties Vremo Inter and Seven Hills were almost as tolerant as Darkmar 21 and recovered quickly from damage. Darkmar 21 also showed high tolerance to attack in 1970, as did the Dutch varieties Rollo, Roodnerf and Stiekema, when large aphid infestations developed on the eight varieties then grown. Lack of plant tolerance to damage appeared to be associated with incurling foliage, a characteristic of Irish Elegance, Cambridge No. 1 and No. 3.     

Comparison of feeding behaviour of two Brassica pests Brevicoryne brassicae and Myzus persicae on wild and cultivated brassica species

Feeding behaviour of the specialist Brassicae aphid, Brevicoryne brassicae (L) (cabbage aphid) and the generalist, Myzus persicae, (Sulzer) (peach potato aphid) was monitored electronically on the susceptible cauliflower, Brassica oleracea var. botrytis cv Newton Seale, and a range of 17 Brassica species, B. carinata, B. juncea, B. nigra, B. macrocarpa, and B. villosa var. drepanensis and cultivated brassica varieties, B. oleracea, B. campestris and B. napus. Aphids, monitored for 10 h on the underside of leaves, performed recognisable feeding behaviour on all brassica species. The main differences in feeding behaviour, between M. persicae and B. brassicae, on the susceptible cauliflower Newton Seale, were fewer probes, shorter times to initially reach the phloem but longer times to establish sustained phloem ingestion and the longer times spent, by M. persicae, in xylem ingestion.Feeding behaviour on the range of brassica species tested indicated that generalist and specialist aphids are influenced differently by the host plant. A longer time spent in xylem ingestion was again the major difference in the feeding behaviour of the two aphids. In addition, rejection of passive phloem ingestion, by M. persicae, was not related so closely to increased time spent in non probing activities, as for B. brassicae. This observation indicates that M. persicae does not generally accept or reject brassica species due to the presence of phagostimulants, such as glucosinolates at the leaf surface or along the stylet pathway, unless the concentration is very high. Differences in feeding strategies employed by generalist and specialist aphids on the same plants are discussed.     

Effects of crop diversification levels and fertilization regimes on abundance of Brevicoryne brassicae (L.) and its parasitization by Diaeretiella rapae (M’Intosh) in broccoli

1 The effects of intercropping via competition on crop yields, pest [cabbage aphid Brevicoryne brassicae (L.)] abundance, and natural enemy efficacy were studied in the Brassica oleracea L. var. italica system. 2 From May to December 2004, insect populations and yield parameters were monitored in summer and autumn in broccoli monoculture and polyculture systems with or without competition from Brassica spp. (mustard), or Fagopyrum esculentum Moench (buckwheat), with addition of organic (compost) or synthetic fertilizer. 3 Competition from buckwheat and mustard intercrops did not influence pest density on broccoli; rather, aphid pressure decreased and natural enemies of cabbage aphid were enhanced in intercropping treatments, but this varied with the intercropped plant and season (summer vs. autumn). 4 In compost‐fertilized broccoli systems, seasonal parasitization rates of B. brassicae by Diaeretiella rapae (M’Intosh) increased along with the expected lower aphid pressure compared with synthetically fertilized plants.     

Studies on broccoli necrotic yellows virus

Electron microscopy of infected D. stramonium cells showed that the virus particles occurred in the cytoplasm. Particles were mostly bacilliform and measured 297 ± 18 times 64 ± 4 nm. In negatively stained leaf homogenates, particles were mostly disrupted; intact particles measured 267 ± 20 times 69 ± 6 nm. In brussels-sprout cells containing BNYV and CIMV, BNYV particles were rarely found compared with those of CIMV, and they occurred within and near CIMV inclusion bodies. BNYV particles were also found in extracts of virus-carrying Brevicoryne brassicae. Broccoli necrotic yellows (BNYV) and cauliflower mosaic (CIMV) viruses occurred together in naturally infected Brussels sprout plants, which showed conspicuous symptoms, and in cauliflower. BNYV was transmitted to and maintained in Datura stramonium and Hyoscyamus niger. It was partially purified from D. stramonium. Using these preparations, from which inhibitor had been removed, BNYV was manually transmitted to cauliflower, causing mild symptoms, and to Brussels sprout, causing a symptomless infection. BNYV also infected Sinapis alba but not cabbage, lettuce, Sonchus oleraceus or Plantago major. BNYV was transmitted by Brevicoryne brassicae but not by Myzus persicae, Hyperomyzus lactucae or Aleyrodes proletella.