Mesocyclops longisetus effects on survivorship of Aedes aegypti immature stages in car tyres

Abstract .The effect of the introduction of the entomophagous copepod Mesocyclops longisetus (Acuacultura F.C.B. strain) on the survival of Aedes aegypti immature stages in car tyres was evaluated under semi-natural conditions in the municipality of Merida, Yucatan, Mexico. Life tables were constructed for the immature stages of the mosquito in the presence and absence of M. longisetus , and the survival data were compared using log–linear models. The data set was adjusted using the GLIM statistical package and the quality of adjustment was evaluated with a chi-squared test . Survivorship curves were constructed for each treatment.
In the absence of M. longisetus , the survivorship of Ae. aegypti immature stages averaged 9%. The highest mortality rate was observed during the fourth larval instar (54%) and the resulting survival pattern corresponded to a type II survivorship curve. The mortality rate of Ae. aegypti first-instar larvae (fifty per tyre) increased more than 200-fold in the presence of M. longisetus (twenty per tyre) and the highest mortality was during the first two larval instars, where it reached 98.9%, with a resulting survivorship of 0.2%. Overall mortality was sixfold greater in the presence of the copepod than in its absence. The survival pattern of immature stages of Ae. aegypti in the presence of the copepod corresponded to a type III survivorship curve. As M. longisetus was so effective against Ae. aegypti immature stages in tyres under semi-natural conditions, its long-term effectiveness should be evaluated under socially and ecologically realistic field conditions in Mexico.     

Geographical variation in dormancy in a copepod: evidence from population crosses

Populations of the freshwater copepod Mesocyclops edax inhabiting Michigan lakes are dormant during winter, whereas populations inhabiting Florida lakes develop and reproduce continuously throughout the year. A Michigan and a Florida population were exposed to dormancy inducing conditions (low temperature and short photoperiod) in the laboratory and observed for indications of dormancy. All Michigan individuals and a small percentage of the Florida individuals entered dormancy as indicated by prolonged duration of the fourth copepodid instar and cessation of feeding. I suggest that in these population these observations represent diapause, rather than quiescence. The two populations were crossbred to examine the nature of inheritance of dormancy. The F₁ hybrids exhibited an incidence of diapause approximately intermediate between the Florida and Michigan parental stocks. The backcrosses of F₁ individuals to the Michigan and Florida stocks, respectively, exhibited a high and an intermediate incidence of diapause. Survival of the F₂ crosses was very low. The present study presents evidence of genetic differentiation between the Michigan and Florida populations of M. edax with respect to ability to diapause.     

Effect of the cyclopoid copepod Mesocyclops thermocyclopoides on the interactions between the predatory rotifer Asplanchna intermedia and its prey Brachionus calyciflorus and B. angularis

In many shallow, eutrophic subtropical ponds, brachionid rotifers are common prey of the predatory copepod Mesocyclops thermocyclopoides. The predatory rotifer Asplanchna intermedia, which is itself a potential prey of the copepod, also feeds preferentially on brachionids. We studied in the laboratory the population dynamics of two mutually competing prey species, Brachionus angularis and B. calyciflorus, in the presence of the two predators A. intermedia and M. thermocyclopoides. The experimental design included separate population dynamics studies with one prey–one predator, two prey–one predator, one prey–two predator, and two prey–two predator systems. These combinations were compared with controls, in which both the prey species (B. angularis and B. calyciflorus) were grown separately and in combination with each other. In the absence of any predator, B. angularis generally eliminated the larger B. calyciflorus. Selective predation by the copepod allowed B. calyciflorus to persist longer in competition with B. angularis. Feeding by M. thermocyclopoides on A. intermedia reduced the predation pressure on B. calyciflorus. However, given enough time, the cyclopoid copepod was able to eliminate both the brachionids as well as the predatory Asplanchna.     

Factors affecting horizontal transmission of the microsporidium Amblyospora albifasciati to its intermediate copepod host Mesocyclops annulatus

Factors that directly impact horizontal transmission of the microsporidium Amblyospora albifasciati to its intermediate copepod host, Mesocyclops annulatus were examined in laboratory bioassays. Results were evaluated in relation to life history strategies that facilitate persistence of the parasite in natural populations of its definitive mosquito host, Ochlerotatusalbifasciatus. A moderately high quantity of meiospores from mosquito larvae was required to infect adult female copepods; the IC50 was estimated at 3.6 × 10⁴ meiospores/ml. Meiospore infectivity following storage at 25 °C was detected up to 30 days, while meiospores stored at 4 °C remained infectious to copepods for 17 months with virtually no decline in infectivity. Uninfected female M. annulatus are long-lived; no appreciable mortality was observed in field-collected individuals for 26 days, with a few individuals surviving up to 70 days. The pathological impact of A. albifasciati infection on M. annulatus resulted in a 30% reduction in survivorship after 7 days followed by gradual progressive mortality with no infected individuals surviving more than 40 days. This moderate level of pathogenicity allows for a steady continual release of spores into the environment where they may be ingested by mosquito larvae. Infected female copepods survived in sediment under conditions of desiccation up to 30 days, thus demonstrating their capacity to function as a link for maintaining A. albifasciati between mosquito generations following periods of desiccation. The susceptibility of late stage copepodid M. annulatus to meiospores of A. albifasciati and subsequent transstadial transmission of infection to adult females was established.     

A laboratory and field evaluation of Macrocyclops distinctus,Megacyclops viridis and Mesocyclops pehpeiensis as control agents of the dengue vector Aedes albopictus in a peridomestic area in Nagasaki,Japan

The use of the cyclopoid copepods Macrocyclops distinctus (Richard) Megacyclops viridis (Jurine) and Mesocyclops pehpeiensis Hu (Cyclopoida: Cyclopidae) as biological control agents against the dengue vector Aedes albopictus (Skuse) (Diptera: Culicidae) was evaluated. In the laboratory their predatory ability was highest against the younger instars of Ae. albopictus and none of the three copepods killed the fourth instar. Except for M. viridis, predatory ability was affected by the size of the container: the smaller the container, the higher the predation. A 4-month field test was conducted to examine the impact of these predators on wild Ae. albopictus. Thirty artificial containers were placed in a peridomestic area to allow Ae. albopictus colonization. We showed continuous and similar oviposition responses in treated and control containers. The densities of Ae. albopictus showed considerable short-term changes and were much reduced by the copepod species. Macrocyclops and the mixture of all three provided better Ae. albopictus control than either Megacyclops or Mesocyclops alone. When larval densities peaked in the control containers in August and September, the overall reduction due to the copepods was nearly complete. Mesocyclops inoculated alone had the highest population survival. However, the growth and survival of all the copepod species was poor when the three genera were mixed. Based on their performance and survival in the trial, Macrocyclops and Mesocyclops merit consideration as bio-control agents of Ae. albopictus.     

Patterns of prey selectivity in the cyclopoid copepod Mesocyclops thermocyclopoides

In the shallow and eutrophic subtropical aquatic ecosystems, which it generally inhabits, the omnivorous copepod Mesocyclops thermocyclopoides encounters a wide variety of animal prey types including ciliates, rotifers, and cladocerans. We studied prey selectivity in laboratory-reared adult females of this species given a choice of (i) prey types belonging to different taxa (ciliates, rotifers, cladocerans, and cyclopoid nauplii), and (ii) different prey species within a taxonomic group differing in body size, morphology or behaviour. We also tested the effect of different proportions of prey species on its selectivity. Prey type proportion had no significant effect on selectivity of the copepod, nor was there any evidence of switching based on the relative abundance of prey. Among the ciliate prey species tested, the largest species, Stylonychia mytilus was positively selected regardless of its relative abundance, while the smallest, S. notophora was selected only when its density was higher. Offered a choice of three species of a brachionid rotifer differing in size, the copepod selected the largest of them, Brachionus calyciflorus, and avoided the smallest B. angularis. The evasive rotifer Hexarthra mira was also avoided. When prey choice included three cladoceran species Daphnia similoides, Moina macrocopa and Ceriodaphnia cornuta, the copepod selected the intermediate-sized M. macrocopa regardless of the abundance of the other two species. Although it fed on Mesocyclops nauplii when there was no choice, M. thermocyclopoides avoided them when alternative food was available. In a multispecies prey choice test, the copepod selected predominantly the rotifer B. calyciflorus and the cladoceran M. macrocopa. We suggest that the prey selectivity patterns shown by M. thermocyclopoides are adaptive in that they lead to ingestion of the most profitable prey.     

Vulnerability of cladoceran species to predation by the copepod Mesocyclops leuckarti: laboratory observations on the behavioural interactions between predator and prey

SUMMARY 1. We analysed the vulnerability of a number of cladoceran species ( Bosmina longirostris , B. fatalis , Diaphanosoma brachyurum , Ceriodaphnia reticulata , Daphnia ambigua and D. pulex ) to predation by Mesocyclops leuckarti in the laboratory.
2. The prey species represented a wide range of body size, morphology, and swimming behaviour. To compare vulnerability, we measured the efficiency of capture and ingestion of each prey species by Mesocyclops . We also measured the rate at which prey were damaged in attacks by Mesocyclops .
3. Mesocyclops preyed effectively on Diaphanosoma and small juvenile Ceriodaphnia but not on Bosmina or Daphnia . Observations suggested that various defence mechanisms, including protruding structures and swimming behaviour and speed, are important in determining prey vulnerability.
4. The body size of Daphnia and Ceriodaphnia seems to be important, because larger animals were better able to escape Mesocyclops attacks. Attacks by Mesocyclops often caused fatal damage, however, even to large Daphnia .     

Secondary production of crustacean zooplankton and biomass of major rotifer species in Lake Bosumtwi/Bosomtwe,Ghana, West Africa

Studies have shown a strong linkage between zooplankton and fisheries' potential in tropical lakes. High zooplankton production provides the basis for fish production, but knowledge of zooplankton production dynamics in African lakes is extremely limited. Crustacean zooplankton production and the biomass of dominant rotifers in Lake Bosumtwi were assessed over a 2‐year period. The crustaceans comprised an endemic and extremely abundant cyclopoid copepod, Mesocyclops bosumtwii and the cladoceran Moina micrura. Mean standing stock of the crustaceans was 429 mg dw m^?3, whilst annual production averaged 2.1 g dw m^?3 y^?1. Production doubled from 1.4 g dw m^?3 y^?1 in 2005 to 2.8 g dw m^?3 y^?1 in 2006. Copepods accounted for 98.5% of crustacean production. The biomass of the dominant rotifers Brachionus calyciflorus and Hexarthra intermedia was less than 1% of total zooplankton biomass. Daily turnover rate and turnover time of the crustaceans was 0.19 day^?1 and 6.2 days respectively. Crustacean production yielded no statistical relationship with phytoplankton biomass. Production was well within the range of tropical lakes. Peak crustacean production synchronized maximum rainfall, lake mixing and phytoplankton production. Most importantly, no one year's set of dynamics can be used to characterize zooplankton production in the lake.