Laboratory evaluation of Mesocyclops annulatus (Wierzejski, 1892) (Copepoda: Cyclopidea) as a predator of container-breeding mosquitoes in Argentina

In laboratory bioassays we tested the predatory capacity of the copepod Mesocyclops annulatus on Aedes aegypti and Culex pipiens larvae. A single adult female of M. annulatus caused 51.6% and 52.3% mortality of 50 first instar larvae of Ae. aegypti and Cx. pipiens respectively, in a 72 h test period. When alternative food was added to the containers, mortality rates declined to 16% and 10.3% for Ae. aegypti and Cx. pipiens respectively. When 50 first instar larvae of each of the two mosquito species tested were placed together with a single adult female of M. annulatus, mortality rates were 75.5% for Ae. aegypti larvae and 23.5% for Cx. pipiens larvae in a three day test period. Different density of adult females of M. annulatus ranged from 5 to 25 females produced mortality rates of Ae. aegypti first instar larvae from 50% to 100% respectively. When a single adult female of M. annulatus was exposed to an increasing number of first-instar Ae. aegypti larvae ranging from 10 to 100, 100% mortality was recorded from 1 to 25 larvae, then mortality declined to 30% with 100 larvae. The average larvae killed per 24 h period by a single copepod were 29.     

Epizootiological studies of Amblyospora albifasciati (Microsporidiida: Amblyosporidae) in natural populations of Aedes albifasciatus (Diptera: Culicidae) and Mesocyclops annulatus (Copepoda: Cyclopidae) in a transient floodwater habitat

The epizootiology of the microsporidium Amblyospora albifasciati was studied in natural populations of its definitive host, a multivoltine, neotropical, floodwater mosquito, Aedes albifasciatus, and its intermediate copepod host, Mesocyclops annulatus, in an ephemeral floodwater habitat during a 12-month period. A. albifasciati was enzootic in mosquitoes. Vertically (transovarially) transmitted meiospore infections occurred regularly and were detected in five of eight larval broods but the prevalence of infection was always low, ranging from 0.5 to 6.9% with an overall average of 0.7%. Horizontal transmission of A. albifasciati infection from copepods to mosquitoes was nominal and limited. It was detected at levels of 6.4 to 20% in larval Ae. albifasciatus populations on two occasions, the month of August and late September through early October. The low levels of horizontal transmission of infection to mosquito larvae appeared to be the principal limiting factor that prevented the proliferation of A. albifasciati in Ae. albifasciatus populations. Copepod populations were abundant from May through September and weekly prevalence rates of A. albifasciati averaged over 50% (range = 5.8 to 100%). The moderately high infection rates in M. annulatus copepods were inconsistent with the low prevalence of meiospore infection in Ae. albifasciatus mosquito larvae. Results suggest that either meiospores of A. albifasciati produced in the mosquito host are highly infectious to copepods or they are long-lived and remain viable within the pool as long as some standing water is present. Observations further indicate that A. albifasciati has a significant detrimental impact on M. annulatus copepod populations but minimal impact on larval populations of Ae. albifasciatus at this site.     

Occurrence of Toxorhynchites guadeloupensis (Dyar Knab) in oviposition trap of Aedes aegypti (L.) (Diptera: Culicidae)

Toxorhynchites guadeloupensis (Dyar Knab), a poorly known mosquito species, was observed preying upon Aedes aegypti (L.) larvae, in an oviposition trap placed for routine dengue entomological surveillance, during 2003-2004 in the urban area of Boa Vista, Roraima, Brazil. This is the first report for Tx. guadeloupensis using Ae. aegypti oviposition traps as breeding places. This finding may have important consequences in the epidemiology and local dengue control since Ae. aegypti density is a basic variable in dengue prediction. Whether predation of Ae aegypti by Tx. guadeloupensis in the Amazon is of significance, is a question to be examined. Also, larval predation may be a cause for underestimation of the actual Ae aegypti numbers. Together these hypotheses need to be better investigated as they are directly related to dengue epidemiology, to the success of any outbreak prediction and surveillance program.     

Combination of Mesocyclops thermocyclopoides and Bacillus thuringiensis var. israelensis: a better approach for the control of Aedes aegypti larvae in water containers.

The efficacy of a local Thai-strain of the copepod, Mesocyclops thermocyclopoides and the larvicide, Bacillus thuringiensis var. israelensis (Bti), used jointly and singly, was studied against Aedes aegypti in water containers. In a laboratory test, copepods alone produced mortality of 98-100% in 1st instar larvae of Ae. aegypti at copepod:larvae ratios ranging from 1:1 to 1:4. In an outdoor field simulated experiment that ran for 16 wk, after a single inoculation, the treatment of copepods and Bti combined yielded the better, more sustainable results than the agents used individually. Numbers of mosquito larvae per sample in the combined treatment were zero during the first 8 wk; larval numbers then increased but were maintained at a very low level for the next 4 wk after which the larval numbers increased moderately but still remained below numbers in the control. Bti alone kept the larvae at the zero level for the first 4 wk after which their numbers increased slightly and were at low levels up to 12 wk. Copepods alone maintained larval numbers at a low level as compared with those of the control. During the course of the experiment the larval numbers in the control were greater than 20 per sample. Statistically significant differences were noted among treatment means (F = 23.083, df = 3/60, P<0.01) over the total period of the study. The number of copepods in the joint treatment was significantly higher than in the copepod alone treatment for the first 8 wk (t = -4.97, df = 14, P<0.01). The density of copepods, however, for the whole 16-wk period was not significantly different in these two treatments (t = -1.51, df = 30, P>0.1).     

Population dynamics of the immature stages of Aedes aegypti (Diptera: Culicidae), vector of dengue: a longitudinal study (1996-2000)

A four year study was conducted on a natural population of immature stages of Aedes aegypti after the re-invasion of Argentina by this vector in 1987. Thirty six plastic containers with 700 ml of dechlorinated water were placed in the La Plata Zoological Garden, La Plata, Argentina. A strip of filter paper around each container was added to facilitate egg counting. Eggs, larvae and pupae were counted weekly in each container from September, 1996 to August, 2000. After egg counting, papers were submerged to facilitate egg hatching and a new paper was placed in each container. Presence of A. aegypti immature stages was recorded from December-January to June during each of the four years of this study. In 1997, 13,105 eggs, 7,978 larvae and 1,476 pupae were registered with 54.7 % positive containers; during 1998, 8,194 eggs, 668 larvae and 142 pupae were recorded with 28.3 % positive containers; 13,510 eggs, 3,690 larvae and 743 pupae were registered during 1999 with 56.7 % positive containers; and 16,327 eggs, 4,669 larvae and 715 pupae during 2000 with 59.3 % of containers with presence of A. aegypti. Egg number and hatching rate were drastically reduced in 1998 when temperatures from December to May were 1 to 2.5 degrees C lower than the other years of this study. These colder than usual temperatures in the summer of 1998 were a consequence of the El Ni?o event.     

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.     

Seasonal profiles of Aedes aegypti (Diptera: Culicidae) larval habitats in an urban area of Costa Rica with a history of mosquito control

Dengue is the most important arboviral disease worldwide and the principal vector-borne disease in Costa Rica. Control of Aedes aegypti populations through source reduction is still considered the most effective way of prevention and control, although it has proven ineffective or unsustainable in many areas with a history of mosquito control. In this study, seasonal profiles and productivity of Aedes aegypti were analyzed in the city of Puntarenas, Costa Rica, where vector control has been practiced for more than ten years. Households contained more than 80% of larval habitats identified, although presence of habitats was more likely in other locations like lots and streets. In the wet season, habitats in the "other" category, like appliances, small manholes, and miscellaneous containers, were the most frequent habitats observed as well as the most common and productive habitats for Ae. aegypti. In the dry season, domestic animal drinking containers were very common, although concrete washtubs contained 79% of Ae. aegypti pupae collected. Individually, non-disposable habitats were as likely or more likely to contain mosquito larvae, and large containers were more likely to harbor mosquito larvae than the small ones only in the dry season. Considering various variables in the logistic regressions, predictors for Ae. aegypti in a habitat were habitat type (p < 0.001), setting (p = 0.043), and disposability (p = 0.022) in the wet season and habitat capacity in the dry season (p = 0.025). Overall, traditional Ae. aegypti larval indices and pupal indices in Puntarenas were high enough to allow viral transmission during the wet season. In spite of continued vector control, it has not been possible to reduce vector densities below threshold levels in Puntarenas, and the habitat profiles show that non-household locations, as well as non-disposable containers, should be targeted in addition to the standard control activities.     

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.     

The influence of larval density, food stress, and parasitism on the bionomics of the dengue vector Aedes aegypti (Diptera: Culicidae): implications for integrated vector management

New larval control strategies for integrated vector management of Aedes aegypti are in high demand, including the use of biological control agents. Exposure of Aedes aegypti to parasites, starvation, and overcrowded conditions during larval development reduces the probability of survival to eclosion, can directly affect fitness parameters such as adult size and fecundity, and can affect the size, provisioning, and viability of eggs produced by females. We compared these parameters after exposing larvae to 1) abundant food at low larval densities, 2) food deprivation and high larval density, and 2) infection with the endoparasite Plagiorchis elegans, an entomopathogenic digenean trematode. Female mosquitoes that eclosed from larval conditions of starvation and overcrowding were smaller and laid fewer and smaller eggs than controls. The proportion of females to complete an oviposition cycle was reduced in the P. elegans-infected treatment group. Parasite load was negatively correlated with wing length and egg size. Infection of Ae. aegypti with P. elegans has sublethal effects and may reduce population-level reproductive output, but one-time low-density P. elegans exposure does not have sufficient effect on Ae. aegypti fitness parameters to be considered a viable biocontrol option.     

Predation potential of three flatworm species (Platyhelminthes: Turbellaria) on mosquitoes (Diptera: Culicidae)

We conducted a field survey for flatworms to select species as potential biological control agents against Aedes aegypti and Culex pipiens (Diptera, Culicidae) breeding in artificial containers. Laboratory experiments were performed to determine the daily predation rate, differential predation on each mosquito larval instar, selective predation on either A. aegypti or C. pipiens, and predator tolerance to water from artificial containers. Girardia anceps (Tricladida, Paludicola, Dugesiidae), Mesostoma ehrenbergii and Bothromesostoma cf. evelinae (Rhabdocoela, Typhloplanoida, Typhloplanidae) were found in temporary puddles and permanent pools. In the laboratory, they killed between 52% and 100% of immature mosquitoes coexisting in the same habitat. No preference of flatworms for mosquito preys was detected. Predation rate was related to predator size and instar of preys. Girardia anceps and B. evelinae survived after a dry period and when re-flooding occurred, they laid eggs. Tolerance to water from artificial containers was highest in G. anceps and this species could be a suitable predator to reduce mosquito populations from artificial containers using an inoculative approach.     

Host-specific variation in Ieaf miner population dynamics: effects on density, natural enemies and behaviour of Stilbosis quadricustatella (Lepidoptera: Cosmopterigidae)

Abstract. 1. We compared high and low density populations of a leaf miner ( Stilbosis quadricustatella (Cham.)) on two host oaks to ascertain mechanisms influencing abundance. High density miner populations occurred on sand live oak, Quercus geminata (Fagaceae), found in homogeneous stands at inland and coastal sites. Quercus nigra , water oak, a patchily distributed inland species, supported a low density leaf miner population.
2. Average foliar nitrogen of Q.geminata was significantly lower than that of Q.nigra , and lad mining period on Q.geminata was correspondingly longer than on Q.nigra .
3. The average leaf area of Q.nigra was significantly greater than that of Q.geminata .
4. Parasitism was significantly greater in Q.geminata miner populations and predation was significantly higher in Q.nigra populations. However, parasitism and predation rates were roughly reciprocal so that overall larval mortality did not differ significantly between hosts.
5. In a laboratory experiment, pupal overwintering survivorship did not differ significantly between moist and dry treatments of the sand and loam soil types that typify Qgeminata and Q.nipra habitats, respectively.
6. Within-leaf miner density on Q.geminata significantly affected larval survivorship, parasitism and predation. Leaf area and within-leaf miner density were positively correlated.
7. We detected no host-patch area or isolation effect on miner densities on coastal Qgeminata and there was no significant gradient of local coastal conditions affecting larval survivorship or natural enemies.
8. Coastal leaf miner densities were significantly higher on oak patch edges than in interiors.     

A comparison of the effects of prey and non-prey neighbours on foraging rates of Epischura nevadensis (Copepoda: Calanoida)

SUMMARY. 1. Adults of the calanoid copepod, Epischura nevadensis , aggregate in situ near the thermocline in Lake Tahoe, California-Nevada. together with adults of another species of calanoid copepod, Diaptomus tyrelli and juveniles of both species. With a series of laboratory predation and algal clearance trials, we show that foraging rates of adult E. nevadensis are determined not only by the density of co-occurring potential prey (small copepods), but also by the presence of co-occurring non-prey neighbours (large, adult copepods). These effects occur at densities and in zooplankton assemblages found naturally, emphasizing the ecological importance of neighbours other than prey on zooplankton feeding.
2. Neighbours are distinguished primarily by size. Although predation rates increase linearly with the densities of small copepods. both algal clearance and predation rates decrease in the presence of large copepods. We also show, with a field predation experiment using small enclosures, that adults are size selective within species and that Diaptomus are selected over conspecifics of the same size.
3. We hypothesize that by reducing foraging rates in the presence of large zooplankton. E. nevadensis avoids predators and reduces predation risk at the cost of reduced energy consumption.     

豚草条纹叶的生态学特性

在一定空间(7238厘米~3)的养虫器内,豚草条纹叶(虫甲)成虫的生殖力随密度的增加而下降。单对饲养的生殖力最高,平均产卵386.7粒;当密度为18和25头时,产卵仅157.6和50.4粒。幼虫期以及蛹期的死亡率,在不同空间中均随密度的增加而增加,随空间的增大,各密度下的死亡率相应减少。食料质量是影响幼虫存活的重要因素之一,用豚草上、中、下部叶片饲养幼虫,其死亡率分别为10％、70.3％和97.6％。幼虫期累计食叶量可达90.58毫克鲜重,随着日龄增加,近似消化力逐渐下降,摄入物质转换为体物质的效率和消化食物转换为体物质的效率随日龄的增加而增加。成熟成虫的取食量基本恒定,平均每48小时食叶28.01毫克鲜重,其近似消化力为64.2％。刚羽化出土的成虫,达到成熟进入生殖生长所需的食叶量约为213.22毫克鲜重。     

Laboratory evaluation of Toxorhynchites splendens (Diptera: Culicidae) for predation of Aedes albopictus mosquito larvae

Biology of the mosquito Toxorhynchites splendens (Wiedemann) was studied in the laboratory to provide baseline data for using the predatory larvae of this species against those of Aedes albopictus (Skuse) in a biological control programme. The mean incubation time of Tx.splendens eggs was 43.8 h and the time required for newly-hatched larvae to initiate predation was 2.5 h. Mean numbers of prey larvae consumed and killed by each Tx.splendens larva totalled 389 and 345 respectively. The larval period of Tx.splendens was not significantly different for rearing individually or in groups of nine, with equal prey density, and duration of larval development was proportional to prey density. In mass rearing, larval cannibalism was usually observed during days 1-3 post-eclosion. The incidence of cannibalism decreased sharply on the fourth day after hatching when some larvae became fourth-instar. Adult female Tx.splendens usually commenced oviposition on day 4 after emergence. The number of eggs laid daily increased on day 7 and the peak oviposition of 6.3 eggs/female/day occurred on day 11. When oviposition containers were provided only intermittently, gravid females of Tx.splendens scattered most of their eggs on the dry floor of the cage. Viability of eggs laid by females aged 4-14 days was high (60-90%) but decreased to less than 40% as the females aged.     

Surveillance of the mosquito Aedes aegypti and its biocontrol with the copepod Mesocyclops aspericornis in Australian wells and gold mines

Abstract. A survey of the dengue vector mosquito Aedes aegypti was undertaken using runnel traps to detect immature stages (larvae and pupae) in flooded disused mine shafts and wells in Charters Towers, Queensland, Northern Australia. The town has a history of dengue fever since 1885 when goldminers were the first recorded victims. During the latest dengue epidemic in 1993, 2% of the population had laboratory-confirmed dengue virus Type 2, despite source reduction of Ae.aegypti breeding-sites at ground level or above. This led to suspicions that dengue vector Ae.aegypti breeding-sites might be below ground level. When surveyed in March 1994, Ae.aegypti immatures were found in 9/10 wells and 1/6 mine shafts. The water in wells and mines had similar characteristics -except that turbidity was higher in the mines, which more often contained predators of mosquito immatures.
The copepod Mesocyclops aspericornis was collected from water in 1/10 wells and 2/6 mine shafts. Laboratory predation trials resulted in 95.5–100% predation by 25 copepods/1 on Ae.aegypti first-instar larvae up to 200 larvae/1. Five wells containing Ae.aegypti in the survey were inoculated with fifty indigenous M.aspericornis , and five wells (one positive and four negative in the survey) were left untreated as controls. Nine months later, in December 1994, Ae.aegypti had been eliminated from all five treated wells but all untreated control wells contained Ae.aegypti , except for one well that contained a natural population of M.aspericornis. The role of wells and mines as winter/ dry season refuges of Ae.aegypti in northern Australia is reviewed, and we recommend the use of M.aspericornis as a cost-effective, environmentally acceptable and persistent agent for the sustainable control of Ae.aegypti , especially in inaccessible breeding sites.     

Induction and costs of tail spine elongation in Daphnia hyalina×galeata: reduction of susceptibility to copepod predation

1. Seasonal field data showed a positive correlation between the tail spine length of Daphnia hyalina × galeata and the density of the copepod Acanthocyclops robustus . Laboratory experiments were designed to assess the mechanisms underlying the induction of tail spine elongation and to test whether this morphology reduced predation on Daphnia juveniles.
2. Both the elongated tail spine morph and control spine morph produced progeny with elongated tail spine when exposed to copepods. Instar increments, calculated from individual body length, showed that individual growth decreased in the presence of copepods. This decrease in individual growth was less pronounced in spined morphs relative to control morphs.
3. Copepods exhibited significantly higher feeding rates on control morph juveniles compared to elongated tail spine morph juveniles.
4. All Daphnia matured at instar 5 even though the control morph neonates took 24–30 more hours to mature in the presence of copepods than in the absence of copepods. Enlarged body and spine lengths of progeny coincided with reduced progeny number during the first six reproductive instars. The disadvantage of the reduced offspring number produced per female was balanced by enhanced survivorship of progeny subjected to copepod predation.     

不同虫态及虫龄大草蛉与七星瓢虫之间的集团内互作

【目的】为明确新疆棉田棉蚜 Aphis gossypii 捕食性天敌之间的集团内捕食效应及其对蚜虫数量的控制作用。【方法】本研究以优势天敌昆虫大草蛉 Chrysopa pallens 和七星瓢虫 Coccinella septempunctata 为对象,以棉蚜为猎物,在温室中利用盆栽棉花,首先观察了2种天敌昆虫之间各虫态及虫龄配对的19个处理在无蚜植株上共存24 h后的存活数,然后观察了2种天敌昆虫配对处理下棉苗上棉蚜数量随时间的变化趋势。【结果】在无蚜棉株上2种捕食性天敌昆虫共存24 h后的存活结果表明：（1）在发育阶段相同的配对组合中,若是成虫则均存活,若是１龄幼虫则大草蛉存活较多,若是末龄幼虫则七星瓢虫存活较多;（2）在有卵的组配中,除七星瓢虫卵不被大草蛉成虫所捕食外,其他5个组配处理中卵均被捕食;（3）在有蛹的配对组合中,除七星瓢虫蛹被大草蛉末龄幼虫捕食外,其他处理下蛹均不被捕食;（4）在成虫与幼虫的配对组合中,七星瓢虫成虫捕食较多的大草蛉1龄幼虫,但不捕食大草蛉末龄幼虫,而大草蛉成虫与七星瓢虫1龄或末龄幼虫之间不发生捕食;(5）在不同龄期幼虫的配对组合中,大草蛉末龄幼虫捕食七星瓢虫1龄幼虫,而七星瓢虫末龄幼虫捕食大草蛉1龄幼虫。在有蚜植株上2种捕食性天敌共存对棉蚜数量具有不同的控制作用：（1）2种捕食昆虫的幼虫各自单独存在（对照）下,蚜虫密度随时间而降低;（2）大草蛉幼虫与七星瓢虫幼虫或成虫配对处理下,棉蚜密度随时间而增大;（3）大草蛉成虫与七星瓢虫幼虫或成虫配对处理下,棉蚜密度随时间而减小。【结论】研究结果说明,大草蛉与七星瓢虫之间存在集团内捕食,但２种天敌共存对棉蚜的控制作用取决于大草蛉虫态, 若大草蛉为幼虫,可使蚜虫密度增大,若为成虫,则使蚜虫密度减小。     

Bionomics of Scymnus (Pullus) louisianae J. Chapin (Coleoptera: Coccinellidae) as a predator of the soybean aphid,Aphis glycines Matsumura (Homoptera: Aphididae)

A field population of Scymnus louisianae Chapin (Coccinellidae) was found attacking soybean aphids, Apis glycines Matsumura (Aphidae), a pest recently introduced into Kentucky. This coccinellid had not previously been found in Kentucky. A greenhouse population of S. louisianae was established and its predation on A. glycines studied under laboratory conditions. Total time to develop from egg to adult was about 20 d. About 70% of immatures survived to adulthood and they consumed approximately 100 aphid nymphs per beetle larva during the beetle's four larval instars. Adults lived for an average of 47 d (mated males) and 63 d (mated females) and, during their total adult lifetime, mated males consumed an average of 665 nymphs and mated females consumed 1261 nymphs. All developmental times and predation rates were comparable to those reported for other aphidophagous Scymnus spp. which, in conjunction with reports that Scymnus spp. are effective predators of cotton aphids, Aphis gossypii Glover, suggests that S. louisianae is a potentially important predator of A. glycines in the southern United States.     

Assessing the impact of density dependence in field populations of Aedes aegypti

Although many laboratory studies of intra-specific competition have been conducted with Ae. aegypti, there have been few studies in natural environments and none that examined density dependence in natural containers at normal field densities. Additionally, current mathematical models that predict Ae. aegypti population dynamics lack empirically-based functions for density-dependence. We performed field experiments in Tapachula, Mexico, where dengue is a significant public health concern. Twenty-one containers with natural food and water that already contained larvae were collected from local houses. Each container was divided in half and the naturally occurring larvae were apportioned in a manner that resulted in one side of the container (high density) having four times the density of the second side (low density). Larvae were counted and pupae were removed daily. Once adults emerged, wing span was measured to estimate body size. Density had a significant impact on larval survival, adult body size, and the time taken to transition from 4(th) instar to pupation. Increased density decreased larval survival by 20% and decreased wing length by an average of 0.19 mm. These results provide a starting point for a better understanding of density dependence in field populations of Ae. aegypti.     

Potential use of antibiotic to improve performance of laboratory-reared Nezara viridula (L.) (Heteroptera: Pentatomidae)

The antibiotic streptomycin added to the drinking water at a concentration of 125 mg/ l during nymphal development of Nezara viridula (L.) (Heteroptera: Pentatomidae)accelerated the development in ca. 2 days, increased survivorship, and doubled adult longevity; nymph survivorship and adult body weight were not affected when compared to control insects. Streptomycin has potential in rearing N. viridula, especially in improving quality of field-collected adults, by mitigating the introduction of pathogenic bacteria, and improving the quality of the population.