The effect of parasitism by the mermithid Romanomermis culicivorax on the dry weight and hemolymph soluble protein content of three species of mosquitoes

The dry weight, hemolymph soluble protein composition, and content of three species of mosquitoes, Culex pipiens, Aedes taeniorhynchus, and Anopheles quadrimaculatus were examined to determine the effects of parasitism by the mermithid nematode Romanomermis culicivorax. The dry weights of infected fourth-stage larvae of all three species were significantly lower than controls. The differences in weight found between infected early and late C. pipiens and A. quadrimaculatus larvae were attributed to the weight of the parasite itself. This difference was not noticeable in A. taeniorhynchus larvae. Hemolymph proteins were severely depleted in all three mosquito species during parasitism by R. culicivorax. Analysis of protein composition by PAGE showed that these depletions were accompanied by a reduction in the number of proteins. Differences between protein composition concentrations were evident between early and late fourthstage control larvae of C. pipiens and A. quadrimaculatus. The concentration of some low-molecular-weight proteins (below 68,000) remained constant between infected and control samples of all three mosquito species.     

Salts and the Infectivity of Romanomermis culicivorax

The effects of common inorganic ions found in freshwater on the infectivity of Romanomermis culicivorax and the survival of its host, Culex pipiens, were tested. In general, the median lethal concentrations found for R. culicivorax were greater than the reported median concentrations of these ions in freshwater but less than the reported maximum natural concentrations. The ion toxicity for R. culicivorax (on a molar basis) increased in the following order: sodium < potassium < calcium; aml chloride < carbonate = sulfate < nitrate < nitrite < phosphate. The larvae of C. pipiens were generally 20 to 75 times as tolerant of higher ion concentrations as were the preparasitic stages of R. culicivorax.     

Chick parasitism by blowflies affects feeding rates in a Mediterranean population of blue tits

Offspring fitness depends on interactions between parental care and environmental constraints. It has been suggested that in altricial birds parents are able to compensate for the detrimental effects of ectoparasites by improving food provisioning. We tested this prediction in a population of blue tits highly parasitized by blowfly larvae. The frequency of parental feeding visits was significantly higher in parasitized broods than in broods experimentally deparasitized. Despite a strong increase in parental care, chicks of parasitized broods were lighter, smaller, and more anaemic than chicks in deparasitized broods. Parents invest more in feeding parasitized young but cannot fully compensate for the negative effects of parasites, hence young are in poor condition at fledging.     

Uptake of Lipids by the Entomophilic Nematode Romanomermis culicivorax

Romanomermis culicivorax juveniles were dissected out of Aedes aegypti larvae 7 days after infection and incubated under controlled conditions in isotonic saline containing a ¹⁴C-labeled fatty acid (palmitic acid), monoacylglycerol (glycerol monoolein), or triacylglycerol (glycerol tripalmate) nutrient source. The mermithid absorbed each of these lipids from the incubation medium, the rate of uptake being greatest for glycerol monoolein. No lipase activity was detected in whole nematode homogenates or in the media in which the nematodes were incubated. It is suggested that the nematode transports complex lipid molecules across its outer cuticle intact.     

Permeability of the Body Wall of Romanomermis culicivorax to Lanthanum

Ultrastructural study of the body wall of preparasitic, parasitic, and postparasitic stages of Romanomermis culicivorax showed that the cuticle of all three stages was permeable to lanthanum. The cuticle of the parasitic stage was the thinnest and showed the greatest permeability. Lanthanum accumulated on the apical surfaces of the hypodermal cells but was not found intracellularly. The negative staining characteristics of lanthanum enhanced the detection of numerous smooth septate junctions in the hypodermis of the parasitic stage.     

The effect of nematode parasitism on the osmolality and major cation concentration in the haemolymph of three larval mosquito species

Parasitism by a mermithid nematode, Romanomermis culicivorax, causes severe depletion of haemolymph carbohydrates and proteins in mosquito larvae. We undertook a study to determine if haemolymph osmolality and cation concentrations were affected also by mermithid parasitism. The haemolymph osmolality of R. culicivorax-infected and control Aedes taeniorhynchus and Culex pipiens fourth-instar larvae was not significantly different. However, the haemolymph osmolality decreased significantly in infected Anopheles quadrimaculatus. Each mosquito species demonstrated significant alterations in the haemolymph concentration of at least one cation when infected although the cation concentrations affected differed for each species. The changes observed were statistically significant but the magnitude of change was not great. Overall, despite the severe nutritional burden of the mermithid nematode, these species of mosquito larvae can continue to maintain osmoregulation.     

Bioassays for comparative infectivity of mermithid nematodes (Romanomermis iyengari,Romanomermis culicivorax and Strelkovimermis spiculatus) for culicine mosquito larvae

Two improved bioassays were developed to establish infectivity baselines for selection experiments using mermithid nematode variants. Comparative infectivity of Romanomermis iyengari, Romanomermis culicivorax and Strelkovimermis spiculatus using larvae of three mosquito spp. Aedes sierrensis, Aedes aegypti and Culex pipiens were evaluated with “plate” and “tray” bioassays at selected intensity of infections. Using the “plate” bioassay, single mosquito larvae were immersed in 2 ml of water within individual depressions of 12-well, polystyrene tissue culture plates. One, three, or five preparasitic juveniles (J2) were added to each well. In the “tray” bioassay, polyethylene trays containing 500 ml water and 100 mosquito larvae were exposed to 500 (5:1, nematode:insect host) or 1000 (10:1) J2s. Percentage infection (PINF, infectivity) and intensity of infection (IINF, #nematodes per infected larvae) number were determined only after emergence of post-parasitic J3 juveniles. Under the bioassay conditions, all three species of nematodes resulted in infections in all mosquito hosts, but R. iyengari exhibited better effectiveness in the parasitism of mosquito larvae. The three species of mosquitoes presented high levels of susceptibility to each of the three species of nematodes, but in general Cx. pipiens and Ae. sierrensis were slightly more susceptible than Ae. aegypti. The “plate” bioassay was more efficient in measurement of infectivity of the mermithid species and in establishing baseline characteristics for these mosquito-parasitic nematodes. The “tray” bioassay was an effective bioassay for large cohorts of both infective juveniles and host larvae and, potential for field interactions.     

Oxygen and the Infectivity of Romanomermis culicivorax

The effects on itffectivity by preparasitic Romanomermis culicivorax resulting from four exposure times to four concentrations of oxygen at three temperatures were studied . Low oxygen (1.8 and 3.1 mg /liter) slowed losses of infectivity. Losses of infectivity were similar under aerobic (6 mg /liter) and microaerobic (0.4 mg /liter) conditions for the first 24 h but thereafter were slower in the microaerobic group. N interactions between temperature and oxygen were found over the ranges tested (15-27 C; 0.4-6.0 mg /liter).     

Nutrient Composition of Romanomermis culicivorax in Relation to Egg Production and Metabolism

The nutrient composition of postparasitic females (newly emerged juveniles, newly molted adults, and spent adults) and eggs of Romanomermis culicivorax was studied. Throughout post-parasitic development, proteins increased and lipids decreased progressively as a proportion of the dry weight; the proportion of glycogen within the nematodes remained stable. The greatest decrease in the lipid moiety occurred during egg production. Eggs contained relatively low levels of lipids (12% dry weight), and ca. 20% of the dry weight of the eggs was unaccounted for by lipid, protein, and glycogen determinations. Chitin, mucoproteins, and peptides were present in the eggs. The fatty acid composition of nematodes remained constant during postparasitic development; eggs contained a similar profile of fatty acids as postparasites, with marginally higher content of unsaturated fatty acids. Radiotracer studies showed that the eggs could oxidize glucose and palmitic acid.     

Effects of toxic Alexandrium species on the survival and feeding rates of brine shrimp, Artemia salina

Zooplankton is an important link between phytoplankton and higher consumers in the marine food chain. To investigate the harmful effects of the toxic dinoflagellate Alexandrium species on zooplankton, 4 strains of Alexandrium spp., isolated from the Chinese coast, were used to test the species' effects on the survival and feeding rates of the brine shrimp, Artemia salina. The experiment was designed to assess the response of A. salina in each stage of its life cycle: nauplii, metanauplii, and adult. Each experiment was conducted in a 500 ml treatment that was added. The toxic treatments consisted of single strains of A. minutum, A. catanella, and A. tamarense (Nanhai and Donghai strain), while non-toxic species (dinoflagellate Prorocentrum donghaiense and diatom Chaetoceros minutissimus) were used as control treatments. An additional phytoplankton treatment consisted of, a mixture of A. tamarense (Nanhai strain) and P. donghaiense. Alexandrium spp. species were found to have lethal effects on the brine shrimp at a density of 2000 cells/ml. All the brine shrimps died within 24-168 hours of inoculation with the 4 treatments each containing single toxic Alexandrium species. During the feeding experiment, toxic Alexandrium spp. caused a reduction in the feeding rates in all the three stages of the life cycle of A. salina, whereas this response was not obvious in the treatment involving the nontoxic species P. donghaiense. The body surface of the brine shrimp that were fed on Alexandrium species was consistently covered by a sticky floc. Mortality of A. salina was observed to increase with the occurrence of the floc. The toxicity of the paralytic shellfish poisons (PSP) produced by the Alexandrium species was not significantly correlated with the survival or the feeding rate of the brine shrimp. When A. tamarense was mixed with P. donghaiense, the lethal effect of A. tamarense decreased, as shown by an increase in the survival and the feeding rates of the brine shrimp. A. salina metanauplii were found at the life stage most sensitive to the toxic algae and hunger. In summary, toxic Alexandrium spp. were found to have lethal effects on A. salina and to restrain the brine shrimp's feeding rate. Nontoxic Prorocentrum mitigated the toxicity of Alexandrium to a certain extent. The results also imply that the sticky material on the surface of the body of the brine shrimp may have been an important lethal factor rather than the PSP toxins.     

Hemolymph pH of the larvae of three species of mosquitoes,and the effect of Romanomermis culicivorax parasitism on the blood pH of Culex pipiens

The hemolymph pHs of late fourth-instar Culex pipiens, Aedes taeniorhynchus, and Toxorhynchites amboinensis were measured with pH-sensitive glass microelectrodes and were slightly alkaline; pH 7.51, 7.62, and 7.37, respectively. The hemolymph pH remained relatively constant during the development of C. pipiens larvae through the third and early and late fourth instars. The hemolymph pH in C. pipiens larvae parasitized with the mermithid nematode Romanomermis culicivorax was unaltered. These measurements provide an approximate pH (ca 7.4) which is normal for the hemolymph of larval mosquitoes, and should be useful for further development of a culture medium for R. culicivorax.     

营养改变对潜蝇姬小蜂寄生行为和寄主取食行为的影响

为了研究营养状态对卵育型寄生蜂潜蝇姬小蜂Diglyphus isaea (Walker)雌蜂的寄主取食行为和产卵寄生行为及其二者行为权衡的影响, 在培养皿条件下, 比较了饥饿、加蜂蜜水和不加蜂蜜水3种营养状态的潜蝇姬小蜂雌蜂对美洲斑潜蝇Liriomyza sativae Blanchard各龄幼虫（低、中、高）的寄生、取食及致死能力。结果表明: 非选择条件下, 3种营养状态寄生蜂对高龄幼虫均具有较高的寄生率, 对中龄幼虫具有较高的取食率, 致死率和致死量之间存在显著性差异。3种状态的寄生蜂对低龄幼虫均没有表现出致死能力。有选择条件下, 饥饿状态的寄生蜂对寄主的寄生率最低（5.0%±1.6%）, 取食率最高（16.0%±2.9%）, 特别是对高龄幼虫的取食率占到了整个寄主食物取食率的91.9%; 加蜂蜜水状态下, 寄生蜂对寄主有最低的取食率（8.3%±0.9%）和致死率（17.7%±1.1%）; 不加蜂蜜水状态下, 寄生蜂对寄主有最高的寄生率（13.3%±1.1%）和致死率（28.4%±1.8%）。综合分析发现, 取食寄主的雌蜂比取食蜂蜜水的雌蜂具有更强的致死能力和活动能力。     

Laboratory infection of blackflies (Simuliidae) and midges (Chironomidae) by the mosquito mermithid, Romanomermis culicivorax

Penetrating infective juveniles of Romanomermis culicivorax usually killed first-stage larvae of Chironomus maturus Johann., Chironomus sp., Simulium damnosum Theo., and S. venustum Say. Nematodes were melanized and died after they entered fourth stage larvae of 2 chironomid species, but no host reaction was evident after entry into fourth-stage blackfly larvae. In contrast, the nematodes initiated development in the latter hosts, which died before the nematodes completed their development.     

The timing of oviposition and larval growth by two tephritid fly species in relation to host-plant development

Abstract. 1. The relationships between the timing of oviposition, larval establishment and host development were studied in the tephritids Tephritis bardanae (Schrank) and Cerajocera tussilaginis (Fab.) which attack flowerheads of Arctium minus (Hill) Bernh. (Compositae).
2. T. bardanae laid eggs in small sized flowerheads that were at an early stage of development, and appeared to use the external dimensions of the head as an oviposition cue. In contrast, C. tussilaginis females laid eggs into heads that were near to flowering and the timing of their attack was most closely related to particular lengths of florets and achenes inside the head. Both tephritids apparently recognized suitable heads by comparing aspects of their own body size with the size of particular flowerhead structures.
3. Individual heads were suitable for oviposition for a period of 10–11 days for both species, but the periods of susceptibility to each species did not overlap.
4. Attack by T. bardanae was timed to exploit the flowering phase of flowerhead development. Larval establishment and early development were synchronized with increasing nutrient availability occurring during the rapid growth of the florets and achenes before and during anthesis.
5. In contrast, the later attack by C. tussilaginis was timed to exploit the seed maturation phase of head development. Individual C. tussilaginis larvae operated as highly specialized 'achene parasites', utilizing the influx of nutrients into single achenes after fertilization.
6. Larvae of both tephritids induced abnormal host-tissue growth, but oviposition in both species was timed primarily to synchronize larval development with natural periods of high nutrient availability inside flowerheads, rather than with the presence of tissues suitable for gall induction.     

中红侧沟茧蜂寄生对粘虫幼虫取食及生长发育的影响

【目的】为明确中红侧沟茧蜂Microplitis mediator(Haliday)寄生对粘虫Mythimna separata(Walker)幼虫取食和发育的影响及评价其田间应用价值。【方法】比较研究了中红侧沟茧蜂寄生不同日龄粘虫对粘虫幼虫取食量和发育的影响。【结果】被寄生的粘虫4、6、8日龄幼虫与未被寄生的同龄期幼虫取食量差异达极显著水平。被寄生的4、6、8日龄粘虫幼虫间的取食量差异不显著。被寄生的幼虫,5 d前体重缓慢上升,之后缓慢下降,所有被寄生的幼虫均不能化蛹。4、6、8日龄粘虫幼虫被寄生后,中红侧沟茧蜂幼虫在其体内的发育历期不同,不同日龄间差异显著,随着日龄的增大显著缩短。【结论】表明该蜂不仅能有效地控制粘虫当代危害,而且在很大程度上能够抑制粘虫的种群数量。     

Effects of toxic Alexandrium species on the survival and feeding rates of brine shrimp, Artemia salina

Zooplankton is an important link between phytoplankton and higher consumers in the marine food chain. To investigate the harmful effects of the toxic dinoflagellate Alexandrium species on zooplankton, 4 strains of Alexandrium spp., isolated from the Chinese coast, were used to test the species' effects on the survival and feeding rates of the brine shrimp, Artemia salina. The experiment was designed to assess the response of A. salina in each stage of its life cycle: nauplii, metanauplii, and adult. Each experiment was conducted in a 500 ml treatment that was added. The toxic treatments consisted of single strains of A. minutum, A. catanella, and A. tamarense (Nanhai and Donghai strain), while non-toxic species (dinoflagellate Prorocentrum donghaiense and diatom Chaetoceros minutissimus) were used as control treatments. An additional phytoplankton treatment consisted of, a mixture of A. tamarense (Nanhai strain) and P. donghaiense. Alexandrium spp. species were found to have lethal effects on the brine shrimp at a density of 2000 cells/ml. All the brine shrimps died within 24-168 hours of inoculation with the 4 treatments each containing single toxic Alexandrium species. During the feeding experiment, toxic Alexandrium spp. caused a reduction in the feeding rates in all the three stages of the life cycle of A. salina, whereas this response was not obvious in the treatment involving the nontoxic species P. donghaiense. The body surface of the brine shrimp that were fed on Alexandrium species was consistently covered by a sticky floc. Mortality of A. salina was observed to increase with the occurrence of the floc. The toxicity of the paralytic shellfish poisons (PSP) produced by the Alexandrium species was not significantly correlated with the survival or the feeding rate of the brine shrimp. When A. tamarense was mixed with P. donghaiense, the lethal effect of A. tamarense decreased, as shown by an increase in the survival and the feeding rates of the brine shrimp. A. salina metanauplii were found at the life stage most sensitive to the toxic algae and hunger. In summary, toxic Alexandrium spp. were found to have lethal effects on A. salina and to restrain the brine shrimp's feeding rate. Nontoxic Prorocentrum mitigated the toxicity of Alexandrium to a certain extent. The results also imply that the sticky material on the surface of the body of the brine shrimp may have been an important lethal factor rather than the PSP toxins.     

Dynamic effects of parasitism by an endoparasitoid wasp on the development of two host species: implications for host quality and parasitoid fitness

1. The study reported here examined growth and developmental interactions between the gregarious larval koinobiont endoparasitoid Cotesia glomerata (Hymenoptera: Braconidae) and two of its hosts that vary considerably in growth potential: Pieris rapae and the larger P. brassicae (Lepidoptera: Pieridae). At pupation, healthy larvae of P. brassicae are over twice as large, in terms of fresh body mass, as those of P. rapae. 2. Clutch size of C. glomerata was manipulated artificially, and the relationship between parasitoid burden and the maximum weight of the parasitised host (= host–parasitoid complex) was measured. In both hosts, the maximum complex weight was correlated positively with parasitoid burden. Compared with unparasitised hosts, however, the growth of P. rapae was increased at significantly lower parasitoid burdens than in P. brassicae. Emerging wasp size was correlated negatively with parasitoid burden in both host species, whereas development time was less affected. 3. After larval parasitoid egress, the weight of the host carcass increased slightly, but not significantly, with parasitoid burden, although there was a strong correlation between the proportion of host mass consumed by C. glomerata larvae during development and parasitoid burden. 4. Clutch size was generally correlated positively with instar parasitised in both hosts, and greater in P. brassicae than in P. rapae. Sex ratios were much more female biased in L1 and L2 P. rapae than in all other host classes. Adult parasitoid size was correlated inversely with host instar at parasitism, and wasps emerging from P. brassicae were larger, and completed development faster, than conspecifics emerging from P. rapae. 5. The data reveal that parasitism by C. glomerata has profound species‐specific effects on the growth of both host species. Consequently, optimality models in which host quality is often based on host size at parasitism or unparasitised growth potential may have little utility in describing the development of gregarious koinobiont endoparasitoids. The results of this investigation are discussed in relation to the potential effectiveness of gregarious koinobionts in biological control programmes.     

Transport of Palmitic Acid Across the Tegument of the Entomophilic Nematode Romanomermis culicivorax

Romanomermis culicivorax juveniles, dissected out of Aedes aegypti larvae 7 days after infection, were incubated under controlled conditions in isotonic saline containing ¹⁴C-U-palmitic acid to investigate the nature of the transport mechanism(s) used by the nematode for transcuticular uptake of palmitic acid. Net uptake of the isotope by the nematode was of a logarithmic nature with respect to time. Uptake of palmitic acid was accomplished by a combination of diffusion and a mediated process which was substrate saturable and competitively inhibited by myristic and stearic acids. Both 2,4-dinitrophenol and ouabain inhibited uptake of palmitic acid and thus supported the hypothesis that the carrier system is of the active transport variety and is coupled to a Na⁺K⁺ ATPase pump.     

Analysis of pre-weaning feeding policies and other risk factors influencing growth rates in calves on 11 commercial dairy farms

Growth rates in pre-weaned calves influence their health, age at first calving and lifetime productivity. Many farms restrict milk rations to encourage solid feed intake and facilitate early weaning, but this can compromise growth. This study determined the milk feeding policies and associated growth rates on 11 commercial dairy farms in South East England, each following their normal management regime. Between 26 and 54 heifers were recruited per farm, providing a final cohort of 492, of which 71% were pure Holstein. Information on calf rearing practices (feeding, weaning, housing) and health was collected via questionnaires and weekly observations. Estimates of actual milk fed (kg solids) between 1 and 63 days were calculated for individual calves. Morphometric data (weight, height, length) were taken at weeks 1, 5 and 9 and at a median age of 7.5 months and growth rates were calculated. Most calves were fed milk replacer via automated feeders (four farms), teat feeder (one) or buckets (four) whereas two farms provided drums of acidified waste milk. Farms fed between 4 and 6 l/day of milk at mixing rates of 10% to 15%, providing 400 to 900 g/day of milk solids. Both skeletal growth rates and average daily weight gain (ADG) increased in the second month of life compared with the first: height growth from 0.17±0.14 to 0.25±0.16 cm/day and ADG from 0.48±0.25 to 0.71±0.28 kg/day. Post-weaning heifers up to 7.5 months had height increases of 0.16±0.035 cm/day and ADG of 0.83±0.16 kg/day. From 1 to 63 days 70% of calves had growth rates <0.7 kg/day and of these 19.6% gained <0.5 kg/day. Mean ADG before 9 weeks varied between farms from 0.52±0.30 to 0.75±0.20 kg/day. This was related to the amount of milk fed at both a farm and individual calf level. Increasing the total milk solids fed between 1 and 63 days from 20.4 to 46.3 kg (the 10^th to 90^th percentile observed) was associated with an increase of 0.11 kg/day ADG. All farms had a wide variation in growth rates despite single feeding policies. Higher circulating immunoglobulin G and IGF1 concentrations were associated with better growth, whereas low temperatures in month of birth, high scores for diarrhoea, respiratory and umbilical disease and large birth size reduced growth. Many commercially grown dairy heifers therefore experienced growth restriction in the pre-weaned period, potentially reducing their health, welfare and productivity.     

Effects of Host Diet on Romanomermis culicivorax,a Mermithid Parasite of Mosquitoes

When larval mosquitoes (Aedes aegypti) infected with the mermithid nematode Romanomermis culicivorax were fed on a diet low in quantity or protein content or both, the number of postparasites which emerged from the hosts decreased and host mortality increased marginally. Parasitic development was prolonged and became asynchronous in nutritionally deprived hosts. Nematodes emerged from insects infected by more than one nematode before the remaining juveniles comprising such infections had completed parasitic development; this resulted in substantial reductions in postparasite nttmbers. Host development was retarded by low protein and/or reduced diets. Postparasites emerging from second and third instars were reduced in size and in the amount of stored nutriment compared to those recovered from hosts fed on a high protein diet ad libitum. A greater proportion of the rnermithids developed into males in hosts fed on reduced diets but not in hosts fed on low protein diets.