Habitat suitability for three species of Anopheles mosquitoes: larval growth and survival in reciprocal placement experiments

Larval habitats of the main malaria vectors in Belize are associated with three distinctly different aquatic environments: marshes with sparse macrophytes and cyanobacterial mats (Anopheles albimanus), tall dense macrophyte marshes (An. vestitipennis), and floating detritus assemblages within freshwater rivers (An. darlingi). We assessed species-specific habitat suitability based upon nutrient characteristics using larval survival rates (SR) and wing lengths (WL) from floating habitat enclosures. Anopheles albimanus showed a high SR (81%) in all three habitats, while An. vestitipennis had a similarly high SR in its own habitat (82%) and An. darlingi's habitat (81%). Anopheles darlingi only showed high SR (85%) in its own habitat. Both An. vestitipennis and An. darlingi showed very low SR in the An. albimanus habitat. There were no significant WL differences among field-caught, laboratory-reared, and experimental populations of An. vestitipennis and An. albimanus, with the exception of An. vestitipennis experimental populations and An. vestitipennis field populations placed in the An. albimanus habitat. Habitat quality indicators, particulate organic carbon (POC), dissolved organic carbon (DOC), and particulate organic nitrogen (PON), were consistently higher in An. vestitipennis habitats than in the habitats of the other two species. Correspondingly, An. vestitipennis adults were larger when measured both as dry mass and from WL. There were no differences in dry mass, lipids, or protein content among the same species reared at different locations. We compared SR and WL among mosquitoes from shaded and unshaded containers to test whether the high mortality rates for An. vestitipennis and An. darlingi in the An. albimanus habitat were due to intense sun exposure. There were no significant differences among developmental times, survivorship, or adult size for shaded versus sun-exposed populations. This indicates that other factors such as larval toxins, predator avoidance, interspecific species competition, etc. may be responsible for the higher mortality rates in those species not adapted to this particular habitat.     

Anopheles albimanus (Diptera: Culicidae) and cyanobacteria: an example of larval habitat selection

Northern Belize has extensive herbaceous wetlands. Those dominated by sparse emergent macrophytes, rushes (Eleocharis spp.) and sawgrass (Cladium jamaicense Crantz), often develop floating mats of cyanobacteria (blue-green algae). These mats provide suitable habitat for larvae of the malaria transmitting mosquito Anopheles albimanus Wiedemann. Presence/absence of A. albimanus larvae and cyanobacterial mats was assessed in marshes located throughout northern Belize. Of the 21 marshes examined during the 1993 wet and 1994 dry seasons, cyanobacterial mats were found in 11 and A. albimanus larvae were detected in 9 of these 11 marshes. No A. albimanus larvae were found in marshes without cyanobacterial mats. Mosquito larvae were collected along two 1,000 m long transects in both the wet season (August 1993) and the dry season (March 1994) to delineate larval distribution in marshes with cyanobacterial mats. A. albimanus larval densities in cyanobacterial mats were relatively high in both seasons: 2.8 and 2.3 larvae per dip in the wet and dry seasons, respectively, in Chan Chen marsh; and 0.8 and 1.02 larvae per dip in Buena Vista marsh. Numbers of larvae per dip did not significantly change with increasing distance from houses/pastures or margins of the marsh. A field experiment showed a strong preference of ovipositing A. albimanus for cyanobacterial mats. Higher temperatures and higher CO2 emissions from cyanobacterial mats are possible ovipositional cues.     

Laboratory and field evaluation of insect repellents as larvicides against the mosquitoes Aedes albopictus and Anopheles albimanus

Acute toxicity and persistence of three insect repellents, deet and two piperidines (AI3-35765 and AI3-37220), were evaluated against mosquito larvae of Aedes albopictus (Skuse) and Anopheles albimanus Wiedemann (Diptera: Culicidae) in the laboratory, and against natural populations of Ae. albopictus in the field. In laboratory studies, the LC50 values of the repellents for first instars ranged between 0.005 and 0.021% (Ae. albopictus) and between 0.01 and 0.014% (An. albimanus) and, for fourth instars, between 0.019 and 0.034% (Ae. albopictus) and between 0.015 and 0.024% (An. albimanus). A 0.1% concentration of deet caused 90-100% mortality in first-instar Ae. albopictus for 4 weeks, whereas AI3-35765 and AI3-37220 at the same concentration killed 95-100% of larvae for 12 weeks and 98-100% of larvae for 33 weeks post-treatment, respectively. Deet and AI3-35765 at 0.1 % concentration resulted in complete mortality of first-instar An. albimanus for 3 weeks post-treatment, whereas AI3-37220 resulted in 91-99% larval mortalities for 35 weeks post-treatment. A 0.1% concentration of A13-37220 provided 77-98% larval mortality for 20 weeks and 63-97% larval mortality for 12 weeks post-treatment, respectively, against fourth-instar Ae. albopictus and An. albimanus.In the field, in artificial containers, the reduction of Ae. albopictus larvae caused by deet, AI3-35765 and AI3-37220 was 88-95% for 3-4 weeks, 98-100% for 7 weeks, and 82-100% for 13 weeks post-treatment, respectively. In used tyres, the same concentration of the repellents resulted in 100% reduction of Ae. albopictus larvae for 2 weeks (deet), 4 weeks (AI3-35765) and 5 weeks (AI3-37220) post-treatment. In cemetery flower vases, Aedes spp. larvae were eliminated for 4 weeks (deet) and 6 weeks post-treatment by both A13-35765 and AI3-37220. These topical repellents (particularly AI3-37220) have good potential for development and use in the management of container-inhabiting mosquitoes because they deter oviposition and kill larvae.     

Effect of Novaluron (Rimon 10 EC) on the mosquitoes Anopheles albimanus, Anopheles pseudopunctipennis, Aedes aegypti, Aedes albopictus and Culex quinquefasciatus from Chiapas, Mexico

Dengue fever is a serious problem in Mexico and vector control has not been effective enough at preventing outbreaks. Malaria is largely under control, but it is important that new control measures continue to be developed. Novaluron, a novel host-specific insect growth regulator and chitin synthesis inhibitor, has proved to be effective against agricultural pests, but its efficacy against larval mosquito vectors under field conditions remains unknown. In accordance with the World Health Organization Pesticide Evaluation Scheme, phase I, II and III studies were conducted to evaluate the efficacy and residual effect of Novaluron (Rimon 10 EC, Makhteshim, Beer-Sheva, Israel) on the malaria vectors Anopheles albimanus Wiedemann (Diptera: Culicidae) and Anopheles pseudopunctipennis Theobald, the dengue vectors Aedes aegypti (L) and Aedes albopictus Skuse and the nuisance mosquito Culex quinquefasciatus Say. Laboratory susceptibility tests yielded diagnostic concentrations for all five target species. Field trials to identify the optimum field dosage of Novaluron against Anopheles mosquitoes were carried out under semi-natural conditions in artificial plots and in vessels with wild mosquitoes. Efficacy was measured by monitoring mortality of larvae and pupae and the percentage of inhibition of emergence from floating cages. Dosages of Novaluron for field tests were based on pupal LC(99) (lethal concentration 99%) of An. pseudopunctipennis (0.166 mg/L) in plots and average pupal LC(99) of Ae. aegypti and Ae. albopictus (0.55 mg/L). At all dosages tested, Novaluron significantly reduced larval populations of An. albimanus, Culex coronator Dyar & Knab, Ae. albopictus and Cx. quinquefasciatus by approximately 90%, inhibited adult emergence of An. albimanus and An. pseudopunctipennis by approximately 97% for almost 4 months in experimental plots, and inhibited adult emergence of Ae. aegypti and Ae. albopictus by approximately 97% for up to 14 weeks. Recommended dosages of Novaluron for non-container breeding and container breeding mosquitoes are 0.166 mg/L and 0.55 mg/L, respectively. Overall, the residual effect was more sustained than that of temephos. The lowest dosage of Novaluron had less of an impact on non-target organisms than did temephos. Small-scale field trials in natural breeding sites treated with Novaluron at 0.6 L/ha eliminated adult emergence of An. albimanus and Cx. coronator for 8 weeks. For phase III studies, Novaluron was tested at the local and village levels, applying the optimum field rate to all natural breeding habitats within 1 km of a pair of neighbouring villages. Village-scale trials of Novaluron at 0.6 L/ha reduced An. albimanus larval populations for at least 8 weeks and, more importantly, sharply reduced the densities of adult host-seeking mosquitoes approaching houses. We conclude that Novaluron is effective and environmentally safer than temephos.     

Spatial Analysis of Effects of Mowing and Burning on Colony Expansion in Reintroduced Black‐Tailed Prairie Dog (Cynomys ludovicianus)

Factors governing the rate and direction of prairie dog (Cynomys spp.) colony expansion remain poorly understood. However, increased knowledge and ability to control these factors may lead to more effective reintroductions of prairie dogs and restoration of grassland habitats. We present density and directional analyses of the establishment of new burrows on three reintroduced colonies of Black‐tailed prairie dog (Cynomys ludovicianus) in southern New Mexico; the study colonies had been subjected to mow and burn treatments in the second year of the study. Our hypotheses were that prairie dogs will preferentially dig new burrows in the treatment plots versus control plots and that the colonies will expand in the direction of the treatment plots. The results support these hypotheses; analysis of burrow counts by site and treatment shows that prairie dogs preferentially colonized both mow and burn treatments compared to untreated areas at the periphery of the colonies. Directional analysis showed a significant posttreatment orientation of new burrows toward the treatment plots for all colonies. Our results show that the direction of expansion of prairie dog colonies can be manipulated. Effective control of the expansion of prairie dog colonies may lead to more successful reintroductions.     

Dynamics of <Emphasis Type="Italic">Typha domingensis</Emphasis> spread in <Emphasis Type="Italic">Eleocharis</Emphasis> dominated oligotrophic tropical wetlands following nutrient enrichment

Recent agricultural intensification in tropical countries has led to increased nutrient input and eutrophication of wetland ecosystems. Higher nutrient levels often lead to changes of vegetation structure and, eventually, shift in species dominance and loss of ecosystem services. We studied the dynamics of species shift in a manipulative nutrient enrichment experiment (+N, +P, +N&P) in oligotrophic wetlands of northern Belize distributed along a salinity gradient. We monitored spread and biomass accumulation of an introduced single individual of Typha domingensis within a 4 years period. The focus was on speed of the spreading and the relative importance of neighbouring ramets in this process. Large differences were found between control and N addition plots versus P and N&P addition plots. The ramets planted in control and N plots died or barely survived, while ramets in P and N&P plots grew vigorously and almost completely outcompeted original vegetation represented by Eleocharis spp. Final numbers of ramets were 2 and 576 per 100 m² for control and N versus P and N&P plots. The filling dynamics of P-enriched plots of differing salinity changed in time. The spreading was delayed in low salinity plots compared to high and medium salinity plots, although it finally reached comparable rates and values. We attribute this delay to originally denser vegetation and less suitable soil conditions in low salinity plots than to a direct salinity effect. Eventually, the number of ramets stabilized and often even decreased, probably due to self-thinning. Spatiotemporal model extrapolating observed vegetative spread suggested that in P-enriched conditions, a clone originating from a single individual is able to cover 1 ha plot completely within 9 years. We conclude that P-enrichment strongly increases the possibility of fast takeover of Belizean wetlands by Typha domingensis. Eventually, such species change can highly increase potential larval habitat for malaria transmitting mosquitoes.     

Avoidance of occupied hosts by the Hessian fly: oviposition behaviour and consequences for larval survival

Abstract 1. Unoccupied wheat plants and wheat plants occupied by conspecific eggs or larvae were presented to ovipositing female Hessian flies in choice tests.
2. The presence of conspecific eggs on the leaf surfaces of wheat plants did not appear to have any effect on the responses of ovipositing Hessian fly females.
3. The presence of conspecific larvae at the base and nodes of wheat plants for 1, 6, or 11 days had significant effects on Hessian fly oviposition. Eggs oviposited on plants were inversely proportional to larval densities and days of larval occupation.
4. Feeding by Hessian fly larvae is associated with several changes in wheat plants. One of these changes, the growth arrestment of the plant, was measured by recording the heights of plants used in oviposition tests. Plant heights were inversely proportional to both larval densities and days of occupation. Plant heights were directly proportional to eggs oviposited on plants.
5. The consequences of adult female avoidance of plants occupied by conspecific larvae were investigated by allowing females to oviposit on unoccupied plants and 1-day, 6-day, and 11-day larval occupied plants, then scoring at the end of the first larval instar the survival of the offspring that resulted from this oviposition.
6. Survival during the first larval instar was 88% for the offspring of females that oviposited on unoccupied plants, decreasing to 82, 31, and 4% on the 1-day, 6-day, and 11-day occupied plant treatments. On these four plant treatments, a positive correlation was found between larval performance (i.e. survival) and the preferences of ovipositing females.
7. On the four plant treatments, relationships between first-instar larval density and first-instar larval survival varied significantly. On unoccupied plants, survival was inversely proportional to density. On plants oviposited on at 6 days of larval occupation, survival was directly proportional to density.     

A comparison of Aedes vigilax larval population densities and associated vegetation categories in a coastal wetland,Northern Territory,Australia

Darwin's northern suburbs border an extensive coastal reed and upper mangrove wetland recognized as an important larval habitat for Aedes vigilax (Skuse), the northern salt marsh mosquito, an established vector for Ross River and Barmah Forest viruses and an appreciable pest species. We sought to identify the most important vegetation categories associated with Ae. vigilax breeding to maximize the efficiency of mosquito control efforts. Using a generalized linear model with negative binominal distribution and log link, this study compares larval densities, determined by focused dipping, between 13 discernable vegetation categories. The incidence rate ratios (RR) generated can be used to compare the magnitude of larval densities for each vegetation category, compared with the reference category. Aedes vigilax larval densities were almost ten times greater in artificial drainage areas (RR=9.82), followed by tide‐affected reticulate (Sporobolus/Xerochloa) areas (RR=8.15), then Schoenoplectus/mangroves (RR=2.29), compared with the reference vegetation category “lower mangroves.” Furthermore, larval densities were highest in May, due to tidal inundation, for drainage areas and tide‐affected reticulates (RR=12.2, 11.7, respectively) compared with March, the reference month. Thus, to maximize the efficiency of aerial salt marsh mosquito control operations in this wetland, larval control is best accomplished by concentrating on drains, Schoenoplectus/mangroves, and tide‐affected reticulate areas, commencing early after the wet season. These results should apply to other areas of salt marsh mosquito breeding across northern Australia.     

Do multitrophic interactions override N fertilization effects on <Emphasis Type="Italic">Operophtera</Emphasis> larvae?

We examined how performance of Operophtera brumata (Lepidoptera) larvae was affected by nitrogen (N) fertilization of boreal forest understorey vegetation. We monitored larval densities on Vaccinium myrtillus plants for a period of 7 years in a field experiment. Preliminary results indicated that the N effect on larval densities was weak. To examine if this was due to indirect interactions with a plant pathogen, Valdensia heterodoxa, that share the same host plant, or due to top-down effects of predation, we performed both a laboratory feeding experiment (individual level) and a bird exclusion experiment (population level) in the field. At the individual level, altered food plant quality (changes in plant concentration of carbon, N, phenolics, or condensed tannins) due to repeated infection by the pathogen had no effect on larval performance, but both survival to the adult stage and adult weight were positively affected by N fertilization. Exclusion of insectivorous birds increased the frequency of larval damage on V. myrtillus shoots, indicating higher larval densities. This effect was stronger in fertilized than in unfertilized plots, indicating higher bird predation in fertilized plots. Predation may thus explain the lack of fertilization effect on larval densities in the field experiment. Our results suggest that top-down effects are more important for larval densities than bottom-up effects, and that bird predation may play an important role in population regulation of O. brumata in boreal forests.Electronic Supplementary Material Supplementary material is available for this article at     

The influence of pruning on wasp inhabitants of galls induced by Hemadas nubilipennis Ashmead (Hymenoptera: Pteromalidae) on lowbush blueberry

The efficacy of pruning methods for managing blueberry stem galls caused by the chalcid wasp, Hemadas nubilipennis (Ashmead), was studied in five commercial lowbush blueberry (Vaccinium angustifolium Aiton) fields in Nova Scotia, Canada, between October 1999 and May 2000. Blueberry fields were mowed in the fall, and burning treatments were subsequently applied either in the fall or the spring. Three treatments were compared: mowing only, mowing plus fall burning, and mowing plus spring burning. Galls collected from the mow plus spring-burn treatment had the least wasp emergence of the three treatments, while the total number of galls was not affected by treatment. Wasp mortality, not gall destruction, is why wasp emergence is reduced in burn treatments. More galls were located and, for the burn treatments, higher wasp emergence was seen from galls found within the leaf litter than those above it. Five co-inhabitants emerged from blueberry stem galls in this study. Three, Eurytoma solenozopheriae (Ashmead), Sycophila vacciniicola (Balduf), and Orymus vacciniicola (Ashmead) are commonly found associates. The other two, Eupelmus vesicularis (Ritzius) and Pteromalus spp., are new records for Nova Scotia. O. vacciniicola is likely an inquiline because it is the largest wasp emerging from galls, and there was a positive relationship between its emergence and that of H. nubilipennis. Larger gall size improved H. nubilipennis emergence from mow and spring-burn galls. After a field has been mowed in the fall, we recommend a spring burn to reduce gall populations and the threat of product contamination.     

Seasonal fire effects on the diversity patterns,spatial distribution and community structure of forbs in the Northern Mixed Prairie,USA

The effects of fire season on forb diversity patterns, density, and composition were determined for a northern Mixed Prairie site, USA. Repeated spring burns (dormant season), summer burns, fall burns (dormant season), and unburned treatments were compared over a 3-yr period characterized by wet and dry moisture conditions. Alpha and beta diversity were highest on unburned and summer burn treatments, while landscape mosaic diversity was highest on fall burns. Forb density was highest on fall and spring burn sites. Nine forb species comprised 82% of total densities and were significantly affected by fire season and year to year variations in moisture. Forb composition for unburned and spring burn treatments was similar, but both treatments were different from the summer burn and fall burn treatments which were similar to each other. Fire alone did not appear to be an intense enough disturbance to initiate drastic changes in the forb component of vegetation patches. Specific fire seasons did appear to either mask or enhance forb structure arising from other disturbance(s). Fire season also affected the scales of forb organization in the landscape. Contrasting spatial characteristics of the forb component of prairie plant communities may provide a diagnostic technique for exposing the interaction of disturbances at different temporal and spatial scales.     

Ookinete destruction within the mosquito midgut lumen explains Anopheles albimanus refractoriness to Plasmodium falciparum (3D7A) oocyst infection

Previous studies have shown that the central American mosquito vector, Anopheles albimanus, is generally refractory to oocyst infection with allopatric isolates of the human malaria parasite Plasmodium falciparum. However, the reasons for the refractoriness of A. albimanus to infection with such isolates of P. falciparum are unknown. In the current study, we investigated the infectivity of the P. falciparum clone 3D7A to laboratory-reared A. albimanus and another natural vector of human malaria, Anopheles stephensi. Plasmodium falciparum gametocytes grown in vitro were simultaneously fed to both mosquito species and the progress of malaria infection compared. In 22 independent paired experimental feeds, no mature oocysts were observed on the midguts of A. albimanus 10days after bloodfeeding. In contrast, high levels of oocyst infection were found on the midguts of simultaneously fed A. stephensi. Direct immunofluorescence microscopy and light microscopical examination of Giemsa-stained histological sections were used to identify when the P. falciparum clone 3D7A failed to establish mature oocyst infections in A. albimanus. Similar densities of macrogametes/zygotes, and immature retort-form and mature ookinetes were found within the bloodmeals of both mosquito species. However, in A. albimanus, ookinetes were seldom associated with the peritrophic matrix, and were neither observed in the ectoperitrophic space nor the midgut epithelium. In contrast, ookinetes were frequently observed in these midgut compartments in A. stephensi. Additionally, young oocysts were observed on the midguts of A. stephensi but not A. albimanus 2days after bloodfeeding. Vital staining of the immature retort-form and mature ookinetes found within the luminal bloodmeal, demonstrated that a significantly greater proportion of these malaria parasite stages were non-viable in A. albimanus compared with A. stephensi. Overall, our observations indicate that ookinetes of the P. falciparum clone 3D7A are destroyed within the bloodmeal of A. albimanus and that the midgut lumen, rather than the midgut epithelium, is the site of mosquito refractoriness in this particular malaria parasite-mosquito vector combination.     

Plasmodium vivax: ookinete destruction and oocyst development arrest are responsible for Anopheles albimanus resistance to circumsporozoite phenotype VK247 parasites

Anopheles albimanus and An. pseudopunctipennis differ in their susceptibilities to Plasmodium vivax circumsporozoite phenotypes. An. pseudopunctipennis is susceptible to phenotype VK247 but almost refractory to VK210. In contrast, An. albimanus is almost refractory to VK247 but susceptible to VK210. To investigate the site in the mosquito and the parasite stage at which resistance mechanisms affect VK247 development in An. albimanus, parasite development was followed in a series of experiments in which both mosquitoes species were simultaneously infected with blood from patients. Parasite phenotype was determined in mature oocysts and salivary gland sporozoites by use of immunofluorescence and Western blot assays and/or gene identification. Ookinete maturation and their densities within the bloodmeal bolus were similar in both mosquito species. Ookinete densities on the internal midgut surface of An. albimanus were 4.7 times higher than those in An. pseudopunctipennis; however, the densities of developing oocysts on the external midgut surface were 6.12 times higher in the latter species. Electron microscopy observation of ookinetes in An. albimanus midgut epithelium indicated severe parasite damage. These results indicate that P. vivax VK247 parasites are destroyed at different parasite stages during migration in An. albimanus midguts. A portion, accumulated on the internal midgut surface, is probably destroyed by the mosquito's digestive enzymes and another portion is most likely destroyed by mosquito defense molecules within the midgut epithelium. A third group, reaching the external midgut surface, initiates oocyst development, but over 90% of them interrupt their development and die. The identification of mechanisms that participate in parasite destruction could provide new elements to construct transgenic mosquitoes resistant to malaria parasites.     

Precipitation and mowing effects on highway rights-of-way vegetation height and safety

Managing highway rights-of-way (HROW) for safety depends upon the annual precipitation received and vegetation mowing practices. This study was conducted along a precipitation gradient in Texas, USA, to evaluate how precipitation and mowing treatments influence vegetation heights. The experiment was initiated in spring 1999 and completed in autumn 2002. Each site had ten treatments with four replications and consisted of forty 15 m × 6 m subplots. Commercial highway mowing equipment was used to mow the subplots at 5-, 10-, or 20-cm heights with an annual mowing frequency of one, two, or three times per year and a non-mowed control. A vegetation height of >30 cm is generally considered a safety hazard. Control subplot vegetation heights increased along the annual precipitation gradient. Most of the subplot vegetation heights at the more arid Andrews site (35 cm precipitation year^?1) were <30 cm. Subplot vegetation heights at the Tahoka (50 cm precipitation year^?1), Brady (66 cm precipitation year^?1), and Lufkin (109 cm precipitation year^?1) locations exceeded 30 cm, regardless of mowing frequency or height. Mowing treatments for HROW safety must be based on site-specific conditions. In areas that receive <35 cm precipitation year^?1, mowing treatments have little effect on vegetation height, and management practices do not necessarily affect visual safety. In areas that receive >35 cm precipitation year^?1, mowing three or less times per year, regardless of mowing height, makes it unfeasible to maintain the vegetation heights of <30 cm needed to maintain the HROW visual safety criterion.     

A geospatial evaluation of Aedes vigilax larval control efforts across a coastal wetland,Northern Territory,Australia

Adjacent to the northern suburbs of Darwin is a coastal wetland that contains important larval habitats for Aedes vigilax (Skuse), the northern salt marsh mosquito. This species is a vector for Ross River virus and Barmah Forest virus, as well as an appreciable human pest. In order to improve aerial larval control efforts, we sought to identify the most important vegetation categories and climatic/seasonal aspects associated with control operations in these wetlands. By using a generalized linear model to compare aerial control for each vegetation category, we found that Schoenoplectus/mangrove areas require the greatest amount of control for tide‐only events (30.1%), and also extensive control for tide and rain events coinciding (18.2%). Our results further indicate that tide‐affected reticulate vegetation indicated by the marsh grasses Sporobolus virginicus and Xerochloa imberbis require extensive control for Ae. vigilax larvae after rain‐only events (44.7%), and tide and rain events coinciding (38.0%). The analyses of vector control efforts by month indicated that September to January, with a peak in November and December, required the most control. A companion paper identifies the vegetation categories most associated with Aedes vigilax larvae population densities in the coastal wetland. To maximize the efficiency of aerial salt marsh mosquito control operations in northern Australia, aerial control efforts should concentrate on the vegetation categories with high larval densities between September and January.     

Effects of hazard-reduction burning on populations of understorey plant species on Hawkesbury sandstone

Density counts were taken for 37 plant species on 12 plots which were assigned to three treatments: spring burn, autumn burn, and control. Post-fire sampling was carried out at intervals of up to 6 years when a second fire treatment was applied, followed by further sampling at 1 year. Most pre-fire species returned by 12 months after fire. Initial recovery was slower on the autumn burn plots and these were surpassed after 12 months by the spring burn plots which remained significantly more diverse until 6 years after fire when the treatments converged. The second fire led to further loss of species, especially on the autumn burn plots. Overall, numbers of individuals were lower in the post-fire community and did not fully recover during the 6 years before the second fire. Of the 37 species followed over the study period, eight had population numbers consistently below pre-fire values, seven showed better recovery on the autumn burn plots, eight showed better recovery on the spring burn plots, and fourteen had population numbers equal to or greater than pre-fire values. Most of the species not fully recovering had relatively poor survival rates. The better recovery rate of species on the autumn burn plots was attributable to better recruitment while the species recovering on the spring burn plots showed better survival and recruitment. The species increasing their numbers after the fire did so through good recruitment or survival, or both. For some species post-fire rainfall or temperature was significantly correlated with greater post-fire recruitment; others were more strongly affected by the treatment itself or more directly by the somewhat different fire intensities in spring and autumn, the differences in soil and litter moisture content, or seasonal variations in soil seed populations.     

Impact of Recombinant Baculovirus Applications on Target Heliothines and Nontarget Predators in Cotton

Recombinant baculoviruses have been genetically engineered to reduce the time to kill infected pests, thus reducing crop damage. In this study, wild-type viruses and recombinant viruses expressing a scorpion toxin were applied to cotton in response to larval infestations of Helicoverpa zea and Heliothis virescens in 1997 and 1998. A chemical standard and an untreated control acted as comparison treatments. The goals of this field study were to (1) assess the efficacy of recombinant baculoviruses in protecting cotton from larval feeding damage; (2) assess the impact of recombinant virus introductions on predator densities and diversity; and (3) determine if cotton predators acquire baculovirus by consuming infected heliothines. When applications were timed at larval emergence, certain recombinant virus treatments protected cotton from damage better than wild-type virus treatments and as well as the chemical standard. Differences in efficacy between recombinant and wild-type baculoviruses were not apparent if treatments were applied 3 to 4 days after peak larval emergence. Predator densities and diversity were similar among recombinant and wild-type baculovirus treatments, whereas plots treated with the chemical standard had consistently smaller predator populations. From polymerase chain reaction analyses of predators in 1997 and 1998, 1.7 and 0.2%, respectively, of predators had consumed a virus-infected heliothine. Nine of the 26 predators carrying viral DNA were positive for recombinant virus. Additionally, 13 of the 26 predators were found to disperse 13.5 to 105 m 2 to 5 days after initial virus applications. Five of these dispersing predators (0.2% of all predators evaluated) carried recombinant viral DNA. These results suggest that the potential for the inadvertent spread of recombinant viral DNA via dispersing predators is low.     

A field experiment on the effectiveness of spiders and carabid beetles as biocontrol agents in soybean

1 Spiders and carabid beetles are abundant generalist predators that prey upon insect pests of soybean. A field experiment was conducted to determine the impact of spiders and carabids on soybean yield. Prior to planting, three 7 × 7 m plots were fenced in order to reduce spider and carabid immigration. Carabids that emerged within the plots were not removed, but spiders that ballooned into these predator‐reduction plots or that entered by climbing the fence were removed by pitfall trapping and searching the vegetation. Three unmanipulated, unfenced plots served as the control treatment. 2 Densities of spiders on soybean vegetation, and activity‐densities of spiders and carabids determined by pitfall trapping, were c. 75% lower in the spider‐carabid reduction treatment than in control plots. Despite clear differences between treatments in numbers and activity of these major generalist predators, the weight of soybeans harvested did not differ between control and spider‐carabid reduction plots. 3 Paralleling the absence of an effect of predator reduction on soybean yield was the absence of any significant difference between treatments in densities of whiteflies (Aleyrodidae), leafhoppers (Cicadellidae), thrips (Thysanoptera), Lepidoptera larvae and herbivorous Coleoptera. 4 Our experiment provides no evidence that spiders and carabid beetles at ambient densities affect soybean yield. Low populations of pest species or low predation pressure on soybean pests by spiders and carabids at the ambient densities of this experiment could be responsible for this result.     

Determination of the resistance to organophosphate, carbamate, and pyrethroid insecticides in Panamanian Anopheles albimanus (Diptera: Culicidae) mosquitoes

Introduction. The susceptibility of Anopheles albimanus to organophosphates, carbamates and pyrethroid insecticides was unknown in the Panama communities of Aguas Claras, Pintupo and Puente Bayano, located in the Amerindian Reservation of Madungandi. This region is considered a malaria transmission area, where An. albimanus is the main vector. Objective. The resistance to organophosphate insecticides, carbamates and pyrethroids was evaluated in field populations of the Anopheles albimanus in Panama. Materials and methods. Progeny of An. albimanus collected in three localities in the indigenous Madugandi region were exposed to bioassays of susceptibility to organophosphate insecticides (fenitrothion, malathion and chlorpyrifos), the carbamate (propoxur) and pyrethroids (deltamethrin, lambdacyhalothrin, cyfluthrin and cypermethrin). The protocols were in accordance with those established for adult mosquitoes by World Health Organization. Results. The three strains of the An. albimanus were resistant to the pyrethroid insecticides deltamethrin, lambdacyhalothrin, cyfluthrin and cypermethrin. Susceptibility remained for the organophosphate insecticides fenitrothion, malathion, chlorpyrifos, and the carbamate insecticide propoxur. Conclusion. The results provided important information to the vector control program, contributing to the application of new strategies on the use of insecticides, and thereby lengthening the life of the insecticide in use.     

Maintenance of chromosome arm integrity between two Anopheles mosquito subgenera

Low-resolution chromosomal homology between Anopheles gambiae and A. albimanus was determined by polytene chromosome in situ cross hybridization of 17 recombinant DNA and PCR products hybridizing to 23 loci. Hybridization results reflect that the chromosomes have rearranged in the form of autosomal whole-arm translocations and numerous paracentric inversions and not by large detectable pericentric inversions or partial arm translocations. An. gambiae and An. albimanus chromosomes hence differ from each other by possessing alternative autosomal arm associations and rearranged internal structure of each arm, but the integrity of the whole arms has remained conserved. In addition, a photomap of the larval salivary gland polytene chromosomes of An. albimanus that we used to identify sites of hybridization in this species is presented that delineates further banding details than maps published in the past.