Microbial larvicides for mosquito control: Impact of long lasting formulations of Bacillus thuringiensis var. israelensis and Bacillus sphaericus on non‐target organisms in western Kenya highlands

The microbial larvicides Bacillus thuringiensis var. israelensis and Bacillus sphaericus have been used extensively for mosquito control and have been found to be effective and safe to non‐target organisms cohabiting with mosquito larvae. Recently developed long lasting microbial larvicides (LLML), although evading the previous challenge of short duration of activity, increase the risk of persistence of toxins in the treated larval habitats. This study monitored the impact of LLML FourStar^® and LL3 on non‐target organisms cohabiting with mosquito larvae in an operational study to control malaria vectors in western Kenya highlands. A total of 300 larval habitats were selected in three highland villages. The habitats were first monitored for 5 weeks to collect baseline data on non‐target organisms cohabiting with mosquito larvae and then randomized into two treatment arms (respective FourStar^® and LL3) and one control arm. Non‐target organisms were sampled weekly for 5 months after treatment to assess the impact of LLML intervention. Before treatment, the mean density of all non‐target organisms combined in the control, LL3 and FourStar^® treated habitats was 1.42, 1.39 and 1.49 individuals per habitat per sampling occasion, respectively. Following treatment, this density remained fairly unchanged for 21 weeks at which time it was 1.82, 2.11, and 2.05 for the respective control, LL3 and FourStar^® treated habitats. Statistical analysis revealed that LL3 and FourStar^® did not significantly alter abundance, richness or diversity of the 11 taxa studied, when comparing the intervention and control larval habitats. However, both FourStar^® and LL3 significantly reduced the density of malaria vectors. In conclusion, one round of label rate application of FourStar^® or LL3 in natural larval habitats did not alter richness, abundance or diversity of the monitored aquatic non‐target organisms cohabiting with mosquito larvae to an ecologically significant level.     

Analysis of the diet of the tadpole shrimp, Triops sinensis, in paddy fields of Shouchang River watershed

The tadpole shrimp, Triops sinensis, was discovered in the paddy fields of the Shouchang River watershed. The gut contents of the shrimp from these field populations were analyzed in order to quantify their dietary patterns. Some species of tadpole shrimps were found to prey on mosquito larvae as well as uproot weeds. Mosquito larvae and weeds were seldom found in the paddy fields which the tadpole shrimp inhabited in the Shouchang River watershed. The results further showed that the larvae of these tadpole shrimp mainly feed on algae and rice lamina. The tadpole shrimp could feed on animal food including protozoa, nematodes, rotifers, crustaceans, and aquatic insect larvae, though the animal food was subsidiary.     

Evaluation of nontarget effects of methoprene applied to catch basins for mosquito control

The mosquito larvicide methoprene is a juvenile growth hormone mimic that is widely used to control mosquito larvae in stormwater catch basins. This study addresses two concerns pertaining to methoprene's use for mosquito control. First, measurements of methoprene concentrations were made from water in catch basins that had been treated with methoprene and from an adjoining salt pond near where the treated catch basins emptied. The concentrations of methoprene in catch basins and at drainage outlets after application at the rates currently used for mosquito control in southern Rhode Island were 0.5 ppb and lower, orders of magnitude below what has been determined as detrimental to organisms other than mosquitoes. Second, the effects of methoprene on the communities that live in catch basins were evaluated both in simulated catch basins in the laboratory and in actual catch basins in the field. We found no evidence of declines in abundances of any taxa attributable to the application. Furthermore, we found no consistent changes in community‐level parameters (e.g., taxonomic richness, and dominance‐diversity relationships) related to methoprene application in either field or laboratory trials.     

Analysis of the diet of the tadpole shrimp, Triops sinensis, in paddy fields of Shouchang River watershed

The tadpole shrimp, Triops sinensis, was discovered in the paddy fields of the Shouchang River watershed. The gut contents of the shrimp from these field populations were analyzed in order to quantify their dietary patterns. Some species of tadpole shrimps were found to prey on mosquito larvae as well as uproot weeds. Mosquito larvae and weeds were seldom found in the paddy fields which the tadpole shrimp inhabited in the Shouchang River watershed. The results further showed that the larvae of these tadpole shrimp mainly feed on algae and rice lamina. The tadpole shrimp could feed on animal food including protozoa, nematodes, rotifers, crustaceans, and aquatic insect larvae, though the animal food was subsidiary.     

Effects of a larval mosquito biopesticide and Culex larvae on a freshwater nanophytoplankton (Selenastrum capricornatum) under axenic conditions

The effects of microbial biopesticides used for mosquito control on autotrophic microorganisms such as nanophytoplankton are equivocal. We examined impacts of mosquito biopesticides and mosquito larvae on primary producers in two independent experiments. In the first experiment, we examined the effects of a commonly used microbial biopesticide formulation (VectoMax^® CG) on a unicellular microalga, Selenastrum capricornatum Printz, under axenic laboratory conditions. The biopesticide treatments included two concentrations (0.008 and 0.016 g liter^?1) of VectoMax^® CG and two controls (one untreated and another with autoclaved 0.016 g VectoMax^® CG liter^?1) in replicated axenic experimental microcosms. Spectrophotometric analysis of chlorophyll a (proxy for algal biomass) and direct enumeration of algal cells following the treatments revealed no significant effects of the microbial biopesticide on algal population growth during the four‐week study. In the second experiment, we tested the effects of different densities of Culex larvae on the population of S. capricornatum. Effects of mosquito larvae feeding on S. capricornatum were significant with a curvilinear relationship between larval density and algal abundance in the water column. Together, these studies demonstrated a lack of direct cytological/toxicological effects of Bacillus‐based microbial pesticides on freshwater primary production and support the hypothesis that the reduction in algal primary production previously reported when Bti products were applied to aquatic environments was likely independent of the Bacillus‐based larvicidal toxins. Instead, it was likely mediated by microbial interactions in the water column and the trophic cascade effects that resulted from the removal of larval mosquitoes. These studies suggest that mosquito larvae independent of pesticide application can influence primary production. Our method of evaluating biopesticides against small photoautotrophs can be very useful for studying the unintended effects on autotrophic microorganisms of other pesticides, including herbicides and pesticides applied to aquatic environments.     

Aquatic microfauna alter larval food resources and affect development and biomass of West Nile and Saint Louis encephalitis vector Culex nigripalpus (Diptera: Culicidae)

Ciliate protists and rotifers are ubiquitous in aquatic habitats and can comprise a significant portion of the microbial food resources available to larval mosquitoes, often showing substantial declines in abundance in the presence of mosquito larvae. This top‐down regulation of protists is reported to be strong for mosquitoes inhabiting small aquatic containers such as pitcher plants or tree holes, but the nature of these interactions with larval mosquitoes developing in other aquatic habitats is poorly understood. We examined the effects of these two microbial groups on lower trophic level microbial food resources, such as bacteria, small flagellates, and organic particles, in the water column, and on Culex larval development and adult production. In three independent laboratory experiments using two microeukaryote species (one ciliate protist and one rotifer) acquired from field larval mosquito habitats and cultured in the laboratory, we determined the effects of Culex nigripalpus larval grazing on water column microbial dynamics, while simultaneously monitoring larval growth and development. The results revealed previously unknown interactions that were different from the top‐down regulation of microbial groups by mosquito larvae in other systems. Both ciliates and rotifers, singly or in combination, altered other microbial populations and inhibited mosquito growth. It is likely that these microeukaryotes, instead of serving as food resources, competed with early instar mosquito larvae for microbes such as small flagellates and bacteria in a density‐dependent manner. These findings help our understanding of the basic larval biology of Culex mosquitoes, variation in mosquito production among various larval habitats, and may have implications for existing vector control strategies and for developing novel microbial‐based control methods.     

Laboratory and field evaluations of industrial formulations of Bacillus thuringiensis serovar. israelensis against some mosquito species of central Italy

Two wettable powder formulations (Bactimos and Vectobac) and a flowable concentrate (Teknar) formulation of Bacillus thuringiensis serovar. israelensis were evaluated as larvicides of Culex pipiens, Aedes caspius, and Aedes detritus. In the laboratory, the levels of susceptibility of these species to the test formulations were essentially similar and corresponded to their relative potencies; the LC₉₀ values ranged from 0.042 to 0.37 ppm. C. pipiens, A. caspius, and A. detritus, in that order, were susceptible to the biocide. Under field conditions in central Italy. Bactimos at 0.5 kg/ha gave 98% control of C. pipiens in an irrigation canal. Teknar at 1.25 liters/ha gave 86–100%, and at 2.5 liters/ha gave 90–100% control of C. pipiens in two natural ponds. Against A. caspius in salt marsh habitats, Bactimos at 0.5 kg/ha and Teknar at 2.5 liters/ha yielded complete control of the larvae, while a lower rate (0.2 kg/ha) of Bactimos, and Vectobac at 0.5 kg/ha resulted in 82–94% and 67–91% control, respectively. Higher rates (0.75 and 1.0 kg/ha) of Vectobac gave 76–100% and 98–100% control of A. caspius. Bactimos at 0.15 kg/ha gave 93–98% control of A. detritus in two salt marsh ponds. B. thuringiensis serovar. israelensis is practically economical for the control of C. pipiens, A. caspius, and A. detritus in the various biotopes in central Italy.     

The efficacy of high and low volume spray applications of Mimic® (tebufenozide) for managing autumn gum moth larvae Mnesampela privata (Lepidoptera: Geometridae) in eucalypt plantations

Abstract 1 The autumn gum moth Mnesampela privata (Guenée) (Lepidoptera: Geometridae, Ennominae) is a native moth that can outbreak, resulting in significant defoliation of plantation eucalypts in southern Australia. 2 Laboratory trials tested M. privata larvae for their dose–response to the ecdysone agonist, Mimic® 700 WP (a.i. 700 g/kg tebufenozide); ground and aerial field trials also tested its efficacy in eucalypt plantations. 3 The laboratory trials showed that there was no significant difference in mortality between larvae treated with 172 g Mimic® (120 g a.i)/ha and those sprayed with doses ranging from 86 to 3340 g Mimic®/ha. 4 Laboratory and field trials demonstrated that second instars were the most susceptible, with the most rapid response. However, second to fourth instars all reached 100% and fifth instars 90% mortality 3 weeks after aerial spraying at 120 g a.i./ha. 5 Aerial spraying an Eucalyptus globulus plantation with 120 g a.i. Mimic® at 20 L/ha caused 95% mortality of instars two to five, and 100% for instars two to four within 3 weeks after spraying. 6 Ground spraying to run‐off with 120 g a.i. Mimic®/ha reduced defoliation of E. grandis from between 67% to 80% for unsprayed trees to 0% defoliation for sprayed trees. 7 The window for effective management of M. privata larvae is 3–5 weeks, during first to third instar development. 8 Replacement of broad‐spectrum insecticides with the more target‐specific Mimic® should increase the biodiversity of plantations and therefore would be more environmentally friendly.     

Efficacy of an esfenvalerate plus methoprene aerosol for the control of eggs and fifth instars of Plodia interpunctella (Lepidoptera: Pyralidae)

Abstract  Aerosol insecticides may provide an alternative to fumigants for control of the Indianmeal moth, Plodia interpunctella (Hübner), the Indianmeal moth, a major insect pest of stored processed food. In this study, eggs and larvae (5th instars) of P . interpunctella were exposed to aerosol applications of the pyrethroid esfenvalerate and insect growth regulator methoprene, alone and in combination, in open and obstructed positions inside small sheds. When larvae were exposed to methoprene alone, adult emergence from those exposed larvae was 7.1%± 1.5%. In contrast, adult emergence was 92.5%± 3.5% when larvae were exposed to esfenvalerate alone. When eggs were exposed to methoprene, adult emergence of those exposed eggs was approximately 75%; however, when eggs were exposed to esfenvalerate, adult emergence was approximately 35%. In the combination treatment of methoprene plus esfenvalerate at their respective label rates, adult emergence following larval exposure was 0.91%± 0.61% compared to 16.3%± 9.6% when eggs were exposed. Based on our results, methoprene alone is highly effective in reducing adult emergence after larval exposure. However, it is not as effective on eggs as esfenvalerate. A combination treatment of esfenvalerate plus methoprene could be used to control eggs and the wandering-phase larval stages of P . interpunctella . An economic risk analysis also supports a strategy of combining methoprene and esfenvalerate.     

Specific detection of Lysobacter enzymogenes (Christensen and Cook 1978) strain 3.1T8 with TaqMan® PCR

Aims: To develop a strain‐specific TaqMan^® PCR method for detecting and quantifying the biocontrol strain Lysobacter enzymogenes 3.1T8. Methods and Results: A primer–probe combination was designed on the basis of a strain‐specific sequence selected using REP‐PCR (repetitive extragenic palindromic‐polymerase chain reaction). The specificity of this combination was demonstrated by 14 other Lysobacter strains that did not react with the selected primer–probe combination. To quantify strain 3.1T8 in cucumber root samples, a calibration curve was prepared by spiking roots with a 10‐fold dilution series of the strain. Detection of the biocontrol strain 3.1T8 with this method showed that the strain survived well for 22 days on root tips as well as on older cucumber roots. Survival was higher when the strain was inoculated to younger plants. In a cucumber production system with large volumes of substrate, strain 3.1T8 was detected in high numbers on cucumber roots 3 weeks after inoculation. Conclusions: The primer–probe combination developed was strain specific, because it did not react with other strains of the same species and genus. The TaqMan^® PCR method successfully quantified the inoculated biocontrol strain on cucumber roots grown in different cropping systems. Significance and Impact of the Study: The developed TaqMan^® PCR method is a strain‐specific real‐time detection method that can be used to assess the population dynamics of L. enzymogenes strain 3.1T8 for further optimization of its biocontrol efficacy.     

Identifying threshold densities for wild deer in the UK above which negative impacts may occur

• 1 At high densities, deer populations may have adverse effects upon and within their environment. In this review we explore published and unpublished information to derive density thresholds for deer species in relation to impacts upon agriculture, forestry, conservation habitats, road traffic, and human and livestock health in the UK. Impact levels are affected by many factors other than absolute density. We therefore seek to establish the range of densities within which negative impacts might start to occur and which should trigger objective monitoring of actual impacts.
• 2 In commercial forestry, a threshold of 4 deer per 100ha has been suggested. Unfenced native woodlands seem to regenerate naturally if there are fewer than 4–5 large deer or fewer than 25 roe deer Capreolus capreolus per 100ha; open habitats may suffer only light or moderate impacts from red deer Cervus elaphus at landscape densities of 7–8 per 100ha.
• 3 Woodland bird species may have declined where deer densities are high but absolute thresholds seem impossible to establish. One study suggests maximum diversity at about 8 white‐tailed deer Odocoileus virginianus per 100ha.
• 4 Deer–vehicle collisions are affected by various factors in addition to deer density, but British and American studies suggest that accident frequencies decline at densities below 7–8 per 100ha.
• 5 Fallow deer Dama dama populations may maintain bovine TB (bTB) infection at much lower densities (25/100ha) than red or roe deer (91/100ha and 200/100ha, respectively) assuming 100% prevalence. Even at 30% prevalence a density of 75 fallow deer per 100ha could maintain bTB within the population.
• 6 We conclude that deer density alone is unlikely to be a good predictor of impact, and suggest that long‐term management should be based on assessment both of actual impacts and apparent density of deer.

     

Tolerance of the planarianDugesia dorotocephala to high concentrations of pesticides and growth regulators

In laboratory tests, the planarianDugesia dorotocephala (Woodworth) was exposed to temephos (0.001 ppm), fenthion (0.003, 0.0035 and 0.004 ppm), malathion (0.1 ppm), chlorpyrifos (0.001 and 0.004 ppm), methoprene (0.005 ppm) and Dimilin ® (0.005 ppm) for 24 h without producing recognizable immediate or delayed effects to the viability, behavior, and asexual reproductive capacity of this planarian.D. dorotocephala tolerated relatively high concentrations of the pesticides and growth regulators suggesting their potential for integrated mosquito control. Post-exposure observations concerning the asexual reproductive capacity ofD. dorotocephala that were initially reared in water with a chloride content of 1200–1500 ppm (type 1 planaria) and 780–870 ppm (type 2 planaria) before experimentation indicated that the degree of asexual reproduction of type I planaria was significantly greater than was observed with type 2 planaria. These results would indicate the possibility of artificially stimulating asexual reproduction, hence mass production by stressingD. dorotocephala in some pesticides and growth regulators and/or by subjecting them to changes in chloride or salinity levels.     

Modeling the Influence of Resource Availability on Population Densities of Oxyops vitiosa (Coleoptera: Curculionidae), a Biological Control Agent of the Invasive Tree Melaleuca quinquenervia

The Australian snout beetle, Oxyops vitiosa, was introduced to south Florida, USA, as a biological control agent of the invasive tree Melaleuca quinquenervia during the spring of 1997. As part of ongoing post-release evaluations of this weevil, we sought to quantify the population density that can be maintained by O. vitiosa larvae when fully exploiting the available melaleuca foliage. Seasonal population densities were modeled as a function of tree size distribution and density, plant phenology, quantity of acceptable foliage (suitable for larval development) and larval consumption values. Larval densities varied dramatically due to fluctuating resource availability and ranged from 830 946 larvae/ha in July–August to >4.5 million larvae/ha in January–February. The expected population density for a generalized (mixed sized) tree distribution was estimated to be 13.9 million larvae/ha. Larval densities increased to 18.8 million larvae/ha per year when large trees (>20 cm diameter at breast height) represented the dominant size class, whereas habitats dominated by medium (10–19 cm) and small (1.3–9 cm) trees were predicted to have larval densities of 11.3 and 6.3 million/year, respectively. Validation data obtained from smaller, more accessible plants suggested that the model overestimated realized yearly larval densities by 9% or 15 416 larvae/ha per year.     

Perturbation and delayed recovery of the reed invertebrate assemblage in Camargue marshes sprayed with Bacillus thuringiensis israelensis

Bacillus thuringiensis var. israelensis (Bti) is the most commonly used larvicide to control mosquitoes worldwide. Considered as nontoxic to most organisms, Bti can nevertheless cause trophic perturbations to natural communities by reducing the abundance of Chironomidae, which are a key element of wetland food webs. Since August 2006, up to 8400 of the 33 000 ha of mosquito larval biotopes in the Camargue (Rhône delta, in southern France), are monitored by a public agency and Bti‐sprayed (aqueous solution of VectoBac 12AS at 2.5 L/ha) whenever mosquito larvae (Ochlerotatus caspius and Oc. detritus) appeared in water bodies. This resulted in 30–50 aerial treatments/year, in addition to ground spraying of unknown frequency. The sprayed habitats include Phragmites australis reedbeds, which support a specific avifauna of conservation concern. We compared the abundance of invertebrate prey available to passerine birds at treated and control sites relative to the predicted values based on hydrology over a 9‐year period. Food available to reed passerines was significantly reduced at treated areas, translating into a 34% decrease in breeding birds based on predictive modeling. The most affected arthropods were Diptera, Aranaea, Coleoptera, and Hymenoptera. No cumulative effects were observed over time, but the recovery of the invertebrate assemblage after the cessation of mosquito control was delayed due to Bti spore persistence and proliferation in the sediments. While hydrology remains a prime factor influencing primary and secondary productivity of the Camargue reed marshes, Bti spraying had significant negative effects on animal communities at several trophic levels.     

Larval habitat for the avian malaria vector Culex quinquefasciatus (Diptera: Culicidae) in altered mid‐elevation mesic‐dry forests in Hawai'i

Effective management of avian malaria (Plasmodium relictum) in Hawai'i's endemic honeycreepers (Drepanidinae) requires the identification and subsequent reduction or treatment of larval habitat for the mosquito vector, Culex quinquefasciatus (Diptera: Culicidae). We conducted ground surveys, treehole surveys, and helicopter aerial surveys from 2001–2003 to identify all potential larval mosquito habitat within two 100+ ha mesic‐dry forest study sites in Hawai'i Volcanoes National Park, Hawai'i; ‘Ainahou Ranch and Mauna Loa Strip Road. At ‘Ainahou Ranch, anthropogenic sites (43%) were more likely to contain mosquitoes than naturally occurring (8%) sites. Larvae of Cx. quinquefasciatus were predominately found in anthropogenic sites while Aedes albopictus larvae occurred less frequently in both anthropogenic sites and naturally‐occurring sites. Additionally, moderate‐size (≈20–22,000 liters) anthropogenic potential larval habitat had >50% probability of mosquito presence compared to larger‐ and smaller‐volume habitat (<50%). Less than 20% of trees surveyed at ‘Ainahou Ranch had treeholes and few mosquito larvae were detected. Aerial surveys at ‘Ainahou Ranch detected 56% (95% CI: 42–68%) of the potential larval habitat identified in ground surveys. At Mauna Loa Strip Road, Cx. quinquefasciatus larvae were only found in the rock holes of small intermittent stream drainages that made up 20% (5 of 25) of the total potential larval habitat. The volume of the potential larval habitat did not influence the probability of mosquito occurrence at Mauna Loa Strip Road. Our results suggest that Cx. quinquefasciatus abundance, and subsequently avian malaria, may be controlled by larval habitat reduction in the mesic‐dry landscapes of Hawai'i where anthropogenic sources predominate.     

Insecticide susceptibility of Culex pipiens pallens (L.) and Aedes albopictus (Skuke) to five commonly used pesticides in the Republic of Korea

Field collected populations of two mosquito species, Culex pipiens pallens and Aedes albopictus, were tested for susceptibility to five pyrethroid insecticides using a topical application bioassay. The laboratory strain of Cx. pipiens pallens (KS‐CP) demonstrated the most and the lowest susceptibility to deltamethrin and d‐cis/trans prallethrine with LD₅₀ values of 0.00022 μg/♀ and 0.00178 μg/♀, respectively, while Ae. albopictus (KS‐AL) showed the greatest and the lowest susceptibility to phthalethrin and deltamethrin with LD₅₀ values of 0.00015 μg/♀ and 0.00085 μg/♀, respectively. Cx. pipiens pallens (JF‐CP) collected at a nearby rice field in Jeonju showed the greatest susceptibility to deltamethrin (LD₅₀ value of 0.0473 μg/♀) and the resistance ratios (RRs) and compared to the laboratory strain were 215 fold greater. JF‐CP demonstrated the lowest susceptibility to d‐cis/trans phenothrin (0.7697 μg/♀) with RRs 711.0 fold greater than the KS‐CP. An Ae. albopictus (JF‐AL) collected at a nearby forest in Jeonju showed the highest susceptibility to deltamethrin (0.00203 μg/♀) with RRs 2.4 fold greater than the KS‐AL. JF‐AL demonstrated the lowest susceptibility to d‐cis/trans prallethrine (LD₅₀ value 0.00646 μg/♀) with RRs 9.4 fold greater than the KS‐AL. JF‐AL demonstrated the greatest resistance to phthalethrin with RRs 39.3 fold greater than the KS‐AL. Resistance ratios of Cx. pipiens pallens between field and laboratory strains ranged from 215.0 to 711.0 and Ae. albopictus ranged from 2.4 to 39.3. These results indicate that the choice of effective insecticides to selected species of mosquito populations will result in more effective control against field strains of mosquito vectors and decrease environmental pollution.     

Juvenile hormone (JH) esterase of the mosquito Culex quinquefasciatus is not a target of the JH analog insecticide methoprene

Juvenile hormones (JHs) are essential sesquiterpenes that control insect development and reproduction. JH analog (JHA) insecticides such as methoprene are compounds that mimic the structure and/or biological activity of JH. In this study we obtained a full-length cDNA, cqjhe, from the southern house mosquito Culex quinquefasciatus that encodes CqJHE, an esterase that selectively metabolizes JH. Unlike other recombinant esterases that have been identified from dipteran insects, CqJHE hydrolyzed JH with specificity constant (k(cat)/K(M) ratio) and V(max) values that are common among JH esterases (JHEs). CqJHE showed picomolar sensitivity to OTFP, a JHE-selective inhibitor, but more than 1000-fold lower sensitivity to DFP, a general esterase inhibitor. To our surprise, CqJHE did not metabolize the isopropyl ester of methoprene even when 25 pmol of methoprene was incubated with an amount of CqJHE that was sufficient to hydrolyze 7,200 pmol of JH to JH acid under the same assay conditions. In competition assays in which both JH and methoprene were available to CqJHE, methoprene did not show any inhibitory effects on the JH hydrolysis rate even when methoprene was present in the assay at a 10-fold higher concentration relative to JH. Our findings indicated that JHE is not a molecular target of methoprene. Our findings also do not support the hypothesis that methoprene functions in part by inhibiting the action of JHE.     

Indirect effects of the fairy shrimp,Branchipus schaefferi and two ostracod species on Bacillus thuringiensis var Israelensis-induced mortality in mosquito larvae

Bacillus thuringiensis var israelensis (BTI), when ingested by mosquito larvae, is highly toxic to them. Many other aquatic invertebrates feed on bacteria but, in general, BTI is not toxic to them. We tested in the laboratory the hypothesis that certain crustaceans indirectly benefit mosquito larvae by reducing mortality caused by BTI. We presumed the mechanism to be ingestion of the bacteria by the crustaceans resulting in a lower concentration available to the mosquito larvae.Mortality of Aedes aegypti larvae exposed to BTI was reduced in the presence of the fairy shrimp, Branchipus schaefferi and the ostracod, Cypridopsis vidua (only during summer trials and not autumn trials for the latter species) but was not reduced in the presence of the ostracod, Heterocypris incongruens. By contrast, H. incongruens preyed upon infected, though still-moving, larvae. Feeding on the bacteria by the crustaceans may not be an important mechanism; our data indicates that the crustaceans did not reduce BTI in the water. Moreover, B. schaefferi, introduced into water and then removed prior to the introduction of BTI and mosquitoes, also reduced mosquito mortality.The mechanism for the protective effect of B. schaefferi and C. vidua is unknown. However, these results suggest that the abundance of certain organisms co-occurring with mosquito larvae may partially explain why the effective concentration of BTI varies among habitats.     

Effect of habitat complexity on the predation of Buenoa fuscipennis (Heteroptera: Notonectidae) on mosquito immature stages and alternative prey

Notonectids are well‐known predators in aquatic habitats, where mosquito larvae, chironomids, and cladocerans constitute their main diet. Our purpose was to assess the effect of structural complexity on the predatory ability of Buenoa fuscipennis, a common predator in aquatic habitats of Buenos Aires city (Argentina). Buenoa fuscipennis showed type 2 functional responses in both the presence and absence of prey refuge and no differences in attack rate or handling time between refuge treatments. Regarding mosquito size classes, B. fuscipennis exhibited a significantly higher preference for 2^nd instar larvae and no predation on pupae. In the presence of mosquito larvae and alternative prey, B. fuscipennis preferred mosquitoes over chironomid larvae and adult cladocerans over mosquito larvae. No switching behavior was detected in our experiments. Habitat structure only slightly affected the predator´s consumption rates on mosquito larvae. Overall, preference for prey did not vary with the presence of refuge, except for the preference for mosquitoes over chironomid larvae, which was significantly decreased in the presence of refuge as a consequence of reduced predation on mosquito larvae. The results suggest that B. fuscipennis could efficiently control mosquitoes in structurally simple habitats where chironomids are the most abundant alternative prey but not in temporary pools where cladocerans are abundant.     

Incipient invasion of Galenia secunda Sond. (Aizoaceae) in Southern Spain

The occurrence of the carpet weed Galenia secunda (L. fil.) Sond. (Aizoaceae) has been reported in Southern Spain. G. secunda is a prostrate perennial species native to South Africa. In this paper, the current distribution of G. secunda and the main habitats invaded in Southern Spain, are reported. The distribution survey revealed an area of occupancy of 92 ha and an extent of occurrence of 14,250 ha for this species, thus suggesting an early stage of invasion. Since the first citation of this species in Spain (1965), our current data (2007) support a rapid spread and invasiveness of G. secunda as a result of an intense rate of coastal development. G. secunda was more often found near roads, because roads facilitate seed dispersal. G. secunda also appeared in other coastal natural habitats such as sand dunes, where G. secunda forms dense monospecific mats. Studies on its invasion potential and impacts in natural habitats are recommended and control measures should be developed to prevent future expansion.