The role of olfaction in host preference by Aedes (Stegomyia) simpsoni and Ae. aegypti

Host preference in females of the mosquitoes Aedes simpsoni (Theo.) and Aedes aegypti (L) appears to be based largely on responses to specific odours at short range, with the site of olfaction being the antennae. In blank Y-olfactometer tests, 48 % of an anthropophilic (llobi) strain of Ae. aegypti responded to one arm and 52% to the other. However, presented with a man's hand in one arm of the olfacto-meter and a whole rat, Arvicanthis niloticus , in the other, 65% responded to man and 35% to the rat. With the same strain in a blank Gouck's type of olfactometer, the response was very poor, only 1 % of the mosquitoes in the olfactometer responded at all, again with no preference for either side. On the introduction of the same hosts into the Gouck's olfactometer, the total response was c. 31 %, of which 72 % responded to man and 28 % to the rat. Elimination of some visual cues affected neither the total response nor the preference. Removing one antenna, reduced the preference for man from about 70 % in the normal mosquitoes to about 58%. The total response remained approximately the same as in the normal mosquitoes. Removing both antennae, in both Ae. aegypti and Ae. simpsoni , caused a sharp depression in the total response and in host discrimination.     

Parasitism of Ascogregarina taiwanensis and Ascogregarina culicis (Apicomplexa: Lecudinidae) in larvae of Aedes albopictus and Aedes aegypti (Diptera: Culicidae) from Manaus, Amazon region, Brazil

The aim of the study was to determine the existence of Ascogregarina spp. in larvae of Aedes albopictus and Aedes aegypti collected in urban and suburban areas of Manaus, Amazon region, Brazil. Between May 2004 and July 2005, the mid-gut of 3rd and 4th instar larvae, collected in tire traps in six neighborhoods of Manaus, was examined for the presence of trophozoites of Ascogregarina. Coexistence of Ae. albopictus larvae infected by A. taiwanensis, and Ae. aegypti larvae by A. culicis, was detected in traps in the field. The percentage of Ae. albopictus larvae infected by A. taiwanensis ranged from 21% to 93.5% and of Ae. aegypti larvae infected by A. culicis from 22% to 95%. The mean infection intensity was similar in both species of Aedes. In traps located in Mauazinho, the replacement of Ae. aegypti by Ae. albopictus larvae was observed. In Manaus, Ae. albopictus larvae were parasitized by A. taiwanensis, and Ae. aegypti larvae by A. culicis. Infection rates were high when the species of Aedes were found separately.     

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.     

Distributions of Competing Container Mosquitoes Depend on Detritus Types, Nutrient Ratios, and Food Availability

Coexistence of competitors may result if resources are sufficiently abundant to render competition unimportant, or if species differ in resource requirements. Detritus type has been shown to affect interspecific competitive outcomes between Aedes albopictus (Skuse) and Aedes aegypti (L.) larvae under controlled conditions. We assessed the relationships among spatial distributions of detritus types, nutrients, and aquatic larvae of these species in nature. We collected mosquitoes, water, and detritus from artificial containers across 24 Florida cemeteries that varied in relative abundances of Ae. aegypti and Ae. albopictus.We measured nutrient content of fine particulate organic matter in water samples as total N, P, and C and ratios of these nutrients. We quantified food availability via a bioassay, raising individual Aedes larvae in the laboratory in standard volumes of field-collected, particulate-containing water from each cemetery. Quantities of detritus types collected in standard containers were significant predictors of nutrients and nutrient ratios. Nutrient abundances were significant predictors of relative abundance of Ae. aegypti, and of larval survival and development by both species in the bioassay. Survival and development of larvae reared in particulate-containing water from sites decreased with decreasing relative abundance of Ae. aegypti. These data suggest that N, P, and C availabilities are determined by detritus inputs to containers and that these nutrients in turn determine the feeding environment encountered by larvae, the intensity of interspecific competition among larvae, and subsequent relative abundances of species at sites. Detritus inputs, nutrients, and food availability thus seem to contribute to distributions of Ae. aegypti and Ae. albopictus in cemetery containers throughout Florida.     

Productivity of natural and artificial containers for Aedes polynesiensis and Aedes aegypti in four American Samoan villages

Six mosquito species were identified in a survey of containers associated with 347 households in four villages in American Samoa. Aedes polynesiensis Marks (Diptera: Culicidae) and Aedes aegypti (L) were the most abundant species, representing 57% and 29% of the mosquitoes identified. Culex quinquefasciatus (Say), Culex annulirostris (Skuse), Aedes oceanicus (Belkin) and Toxorhynchites amboinensis (Doleschall) were also found. Aedes aegypti and Ae. polynesiensis showed distinct differences in their use of containers, preferring large and small containers, respectively. By contrast with previous studies, Ae. polynesiensis utilized domestic and natural containers with equal frequency, whereas Ae. aegypti continued to be found predominantly in domestic containers. Only 15% of containers holding immature mosquitoes included pupae and fewer than 10 Aedes spp. pupae were found in most containers with pupae. An estimated 2289 Ae. polynesiensis and 1640 Ae. aegypti pupae were found in 2258 containers. The presence of both species in the same container did not affect the mean density of either species for larvae or pupae. Glass jars, leaf axils, tree holes and seashells produced few Aedes spp. pupae in any of the study villages. Overall, 75% of Ae. polynesiensis pupae were found in buckets, ice-cream containers and tyres, with <7% being produced in natural containers, whereas 82% of Ae. aegypti pupae were found in 44-gallon (US) drums ( approximately 166L), buckets and tyres. Source reduction efforts targeting these container types may yield significant reductions in both Ae. polynesiensis and Ae. aegypti populations in American Samoa.     

Factors influencing nuisance blackfly (Diptera: Simuliidae) activity in the Scottish Highlands

Abstract. The nuisance activity of blackflies (Diptera: Simuliidae) was investigated in several habitats on Speyside, near Kincraig (57^o08'N, 3^o56'W), Invernesshire, in central Scotland during May-October 1987-89.
The main blackfly species caught landing/biting on humans were Simulium reptans, S. argyreatum, S. variegetum and the S. tuberosum complex, in order of prevalence. Blackfly biting activity occurred from mid-May to mid-September. Numbers of female blackflies attracted to volunteers were correlated with their body posture, habitat and the season. Overall, Simulium activity was greatest in mixed birch/juniper forest, least in spruce plantations and at intermediate levels on pasture, moorland and in Scots Pine forest.
Compared with an adult, a child experienced twice as many Simulium bites per hour (12.2 v 6.3) in the birch forest. On the child's body, 69% of blackfiies landed on the head, neck and back, whereas the majority landed on the legs (48%) and arms (28%) of adults. Bending over, especially during the exertion of gardening, was more attractive to anthropophilic blackfiies than standing or kneeling.     

Evaluation of some adhesives for collecting Musca domestica and Chrysomya megacephala adults or mosquito larvae in sticky traps

1. Seven types of water-insoluble adhesives were evaluated in sticky traps for collecting adults of Musca domestica L. and Chrysomya megacephala (Fabricius) or mosquito larvae (Aedes aegypti (L.) and Culex quinquefasciatus Say). 2. Adhesive viscosity affected the tackiness of the glues and this determined their trapping efficiency in air or water. 3. From the 'Hyvis' range of adhesives tested, 'Hyvis 200' was most effective for trapping adult flies. 4. With 24 h exposure to fourth instar Ae.aegypti larvae in tapwater, submerged plates coated with 'Hyvis 10', 'Hyvis 30' or 'Hyvis 200' formulations trapped the majority of larvae. In polluted water the highest rates of trapping were 17.3% of Ae.aegypti and 18.7% of Cx quinquefasciatus with 'Hyvis 200'. Floating traps were consistently less productive than submerged traps under laboratory conditions. 5. In a heavily polluted natural breeding-site of Cx quinquefasciatus, floating traps were more productive than submerged sticky traps with four of seven adhesives tested, the most efficient being 'Hyvis 200' (4.2 mosquitoes per hour) and Hyvis:polyethylene 90:10 (4.5/h). Despite the relative inefficiency of aquatic traps, emergent adults, pupae and second to fourth instars of larvae were collected quickly from the habitat.     

Biological control of Culicidae with the copepod Mesocyclops aspericornis and larvivorous fish (Poeciliidae) in a village of French Polynesia

The copepod Mesocyclops aspericornis Daday and the larvivorous fishes Gambusia affinis (B. & G.) and Poecilia reticulata R. & B., were released into mosquito breeding sites in Tuherahera village, Tikehau atoll, French Polynesia, to control larvae of Aedes aegypti (L.), Ae.polynesiensis Marks, Culex annulirostris Skuse and Cx quinquefasciatus Say. Treatments were completed within a week, in January 1990. Fish quickly eliminated mosquito larvae from the open breeding sites (ponds, wells). The impact of copepods in water tanks, drums and covered wells was inconsistent, apparently depending on the availability of microfaunal diet for growth of copepod nauplii. As the biting rate of adult Ae.aegypti seemed to be unaffected by the biological control of larvae, this village-scale experiment was judged to be unsuccessful as a means of vector control.     

A laboratory investigation of mosquito larval predation by Toxorhynchites moctezuma on Aedes aegypti

1. Functional responses of predatory Toxorhynchites moctezuma (Dyar & Knab) larvae feeding on Aedes aegypti (L.) larvae (Diptera: Culicidae) were found to be type II of Holling (1959) and Rogers (1972). 2. Estimates of searching rate were generally higher for later instar predators. The search rate of second instar predators declined as prey instar increased, but fourth instar Tx. moctezuma had the highest search rate for second instar Ae. aegypti. 3. Prey handling times were higher for early instar predators and late instar prey. 4. When presented with mixtures of two instars of Ae. aegypti, second instar Tx. moctezuma showed frequency independent selectivity for the early instars, whereas fourth instar predators showed frequency independent selectivity for the late instars of Ae. aegypti. There was no evidence of frequency dependent predation. Preferences appeared to be transitive. 5. Extended random predator equations, using parameters derived from the functional responses, did not adequately describe the outcome of predation in the prey mixture experiment, even when the possibility of optimal switching behaviour was accounted for.     

Comparison of the insecticide susceptibilities of laboratory strains of Aedes aegypti and Aedes albopictus

A susceptible strain of Aedes albopictus derived from the Gainesville strain (Florida, USA) was established in our laboratory. The larvicidal efficacies of the neurotoxic insecticides temephos, permethrin and the pure cis and trans-permethrin isomers and the microbial insecticide Bacillus thuringiensis israelensis (Bti) against Ae. albopictus were estimated and compared to a susceptible strain of Aedes aegypti. The larvicidal effect of insect growth regulator pyriproxyfen was also evaluated in both mosquito strains. The median lethal concentration/median emergency inhibition values for Ae. aegypti and Ae. albopictus, respectively, were: temephos, 3.058 and 6.632 ppb, permethrin, 3.143 and 4.933 ppb, cis-permethrin, 4.457 and 10.068 ppb, trans-permethrin, 1.510 and 3.883 ppb, Bti, 0.655 and 0.880 ppb and pyriproxyfen, 0.00774 and 0.01642 ppb. Ae. albopictus was more tolerant than Ae. aegypti to all six larvicides evaluated. The order of susceptibility for Ae. aegypti was pyriproxyfen > Bti > trans-permethrin > temephos > permethrin > cis-permethrin and for Ae. albopictus was pyriproxyfen > Bti > trans-permethrin > permethrin > temephos > cis-permethrin. Because both species can be found together in common urban, suburban and rural breeding sites, the results of this work provide baseline data on the susceptibility of Ae. albopictus to insecticides commonly used for controlling Ae. aegypti in the field.     

Laboratory and field evaluation of the effects of the neonicotinoid imidacloprid on the oviposition response of Aedes (Stegomyia) aegypti Linnaeus (Diptera: Culicidae)

In this paper, we assessed the suitability of using the neonicotinoid imidacloprid with standard ovitraps by evaluating the ovicidal properties of imidacloprid and its influence on the oviposition response of gravid females of Aedes (Stegomyia) aegypti Linnaeus (Diptera: Culicidae). First, we calculated the imidacloprid lethal dose 99 (LD(99)) by exposing third instar larvae of the target species to different concentrations of the insecticide. Next, Ae. aegypti eggs were exposed to the imidacloprid LD(99) for 24 h and hatching inhibition was recorded. Finally, we investigated any potential repellent effect of the imidacloprid solution on the oviposition response of gravid Aedes females in field and laboratory conditions. The LD(99) obtained from larvae tests proved to be sufficient to keep any exposed eggs from hatching. No repellent effect was observed; females laid as many eggs in imidacloprid-treated ovitraps as in traps containing either clean water or temephos-treated water in both field and laboratory conditions. Our results indicate that imidacloprid is a suitable insecticide for treating ovitraps against Ae. aegypti.     

Larval development of Aedes aegypti and Aedes albopictus in peri-urban brackish water and its implications for transmission of arboviral diseases

Aedes aegypti (Linnaeus) and Aedes albopictus Skuse mosquitoes transmit serious human arboviral diseases including yellow fever, dengue and chikungunya in many tropical and sub-tropical countries. Females of the two species have adapted to undergo preimaginal development in natural or artificial collections of freshwater near human habitations and feed on human blood. While there is an effective vaccine against yellow fever, the control of dengue and chikungunya is mainly dependent on reducing freshwater preimaginal development habitats of the two vectors. We show here that Ae. aegypti and Ae. albopictus lay eggs and their larvae survive to emerge as adults in brackish water (water with <0.5 ppt or parts per thousand, 0.5-30 ppt and >30 ppt salt are termed fresh, brackish and saline respectively). Brackish water with salinity of 2 to 15 ppt in discarded plastic and glass containers, abandoned fishing boats and unused wells in coastal peri-urban environment were found to contain Ae. aegypti and Ae. albopictus larvae. Relatively high incidence of dengue in Jaffna city, Sri Lanka was observed in the vicinity of brackish water habitats containing Ae. aegypti larvae. These observations raise the possibility that brackish water-adapted Ae. aegypti and Ae. albopictus may play a hitherto unrecognized role in transmitting dengue, chikungunya and yellow fever in coastal urban areas. National and international health authorities therefore need to take the findings into consideration and extend their vector control efforts, which are presently focused on urban freshwater habitats, to include brackish water larval development habitats.     

Serratia odorifera a Midgut Inhabitant of Aedes aegypti Mosquito Enhances Its Susceptibility to Dengue-2 Virus

Mosquito midgut plays a crucial role in its vector susceptibility and pathogen interaction. Identification of the sustainable microflora of the midgut environment can therefore help in evaluating its contribution in mosquito-pathogen interaction and in turn vector competence. To understand the bacterial diversity in the midgut of Aedes aegypti mosquitoes, we conducted a screening study of the gut microbes of these mosquitoes which were either collected from fields or reared in the laboratory "culture-dependent" approach. This work demonstrated that the microbial flora of larvae and adult Ae. aegypti midgut is complex and is dominated by Gram negative proteobacteria. Serratia odorifera was found to be stably associated in the midguts of field collected and laboratory reared larvae and adult females. The potential influence of this sustainable gut microbe on DENV-2 susceptibility of this vector was evaluated by co-feeding S. odorifera with DENV-2 to adult Ae. aegypti females (free of gut flora). The observations revealed that the viral susceptibility of these Aedes females enhanced significantly as compared to solely dengue-2 fed and another gut inhabitant, Microbacterium oxydans co-fed females. Based on the results of this study we proposed that the enhancement in the DENV-2 susceptibility of Ae. aegypti females was due to blocking of prohibitin molecule present on the midgut surface of these females by the polypeptide of gut inhabitant S. odorifera.     

The first report of Aedes (Stegomyia) albopictus in Haiti

Aedes albopictus was found in six of the 10 departments of Haiti and in 14 of the 35 communes surveyed. The survey found the larvae of Ae. albopictus in 13 different types of containers. Used tires and tins were by far the most common breeding sites used by this mosquito species. At the breeding sites, Ae. albopictus was associated with other mosquito species, such as Aedes aegypti, Culex nigripalpus and Aedes mediovittatus. The highest proportion of association was with Ae. aegypti. This study represents the first report of Ae. albopictus in Haiti.     

Effects of temperature, pH and salinity on the infection of Leptolegnia chapmanii Seymour (Peronosporomycetes) in mosquito larvae

The effects of temperature, pH, and NaCl concentrations on the infectivity of zoospores of Leptolegnia chapmanii (Argentine isolate) were determined for Aedes aegypti and Culex pipiens under laboratory conditions. Zoospores of L. chapmanii were infectious at temperatures between 10 and 35 degrees C but not at 5 or 40 degrees C. At the permissive temperatures, mortality rates in young instars were much higher than in older instars and larvae of Ae. aegypti were more susceptible to L. chapmanii than larvae of Cx. pipiens. At 25 degrees C, Ae. aegypti larvae challenged with L. chapmanii zoospores resulted in 100% infection at pH levels ranging from 4 to 10. Larvae of Cx. pipiens exposed to similar pH and zoospore concentrations resulted in increasing mortality rates from 62% to 99% at pH 4 to 7, respectively, and then decreased to 71% at pH 10. Aedes aegypti larvae exposed to L. chapmanii zoospores in NaCl concentrations ranging from 0 to 7 parts per thousand (ppt) at 25 degrees C resulted in 100% mortality while mortality rates for Cx. pipiens decreases from 96% in distilled water to 31.5% in water with 6 ppt NaCl. Control Cx. pipiens larvae died when exposed at a NaCl concentration of 7 ppt. Vegetative growth of L. chapmanii was negatively affected by NaCl concentrations. These results have demonstrated that the Argentinean isolate of L. chapmanii tolerated a wide range of temperatures, pH, and salinity, suggesting that it has the potential to adapt to a wide variety of mosquito habitats.     

Food as a limiting factor for Aedes aegypti in water-storage containers.

An understanding of the ecological factors that regulate natural populations of Aedes aegypti mosquitoes can improve control and reduce the incidence of dengue (DF) and dengue hemorrhagic fever (DHF) in tropical areas. We investigated whether immature Ae. aegypti in water-storage containers from an urban area were under food limitation. We used starvation resistance (number of days alive without food) as an indicator of the feeding history in third-instar Ae. aegypti larvae. Resistance to starvation and other measures of immature success, such as development time, survival, and adult mass, were investigated across a wide range of feeding conditions in the laboratory. Resistance to starvation of third-instar larvae and body mass of adults emerging from pupae collected in water-storage containers in an urban area were compared with the laboratory results. If resistance to starvation and adult mass of field-collected Ae. aegypti corresponded with the lower levels of feeding in the laboratory, then food limitation could be inferred in field-collected larvae. Results showed that resistance to starvation was well correlated with previous feeding levels and with the other measures of immature success. Both resistance to starvation and adult body mass of field-collected specimens corresponded with the lower levels of feeding in the laboratory. Therefore, it was concluded that food limitation or competition is likely to be a regulatory factor in water-storage containers in the urban area. It is recommended that any control measure applied to immature Ae. aegypti in water-storage containers should eliminate all or most of the individuals, otherwise unintended, undesirable results might occur, such as the production of more and larger adults.     

Mosquito density, biting rate and cage size effects on repellent tests

Mosquito biting rates and the mean duration of protection (in hours) from bites (MDPB) of Aedes aegypti and Anopheles quadrimaculatus , using the repellent 'deet' ( N , N -diethyl-3-methylbenzamide) on a 50 cm² area of healthy human skin, were observed in small (27 l), medium (≈65 l) and large (125 l) cages containing low, medium or high densities of mosquitoes: respectively, 640, 128 or 49 cm³ of cage volume per female. At the initial treatment rate of ≈ 0.4 μl/cm² (1 ml of 25% deet in ethanol on 650 cm² of skin), the MDPB for deet against Ae. aegypti ranged from 4.5 to 6.5 h and was significantly less (5.0 ± 0.8 h) in large cages compared with medium (6.2 ± 0.9 h) and small (6.2 ± 0.8 h) cages, regardless of the density. Against An. quadrimaculatus the MDPB for deet 0.4 μl/cm² was 1.5–8.0 h, less in small (3.7 ± 2.3 h) and large (2.2 ± 1.1 h) cages at medium (3.7 ± 2.3 h) and high (2.5 ± 1.7 h) mosquito densities, and was longest in medium cages (6.2 ± 2.6 h) at low mosquito densities (5.8 ± 2.8 h). With equinoxial photoperiodicity (light on 06.00–18.00 hours) the biting rate was influenced by the time of observation (08.00, 12.00, 16.00 hours) for Ae. aegypti but not for An. quadrimaculatus. For both species, the biting rate was inversely proportional to mosquito density and the MDPB. The shortest MDPBs were obtained in large cages with high densities of mosquitoes and longest protection times occurred in medium sized cages with low mosquito densities.     

Susceptibility of ten species of mosquito larvae to the parasitic nematode Romanomermis iyengari and its development

Ten species of mosquitoes (Diptera: Culicidae) from five genera were exposed to preparasites of the tropical mermithid nematode species Romanomermis iyengari (Welch) (Nematoda: Mermithidae), a strain isolated in 1978 from Pondicherry. By exposing mosquito larvae during the second instar, nematode infection was invariably lethal, the rate being highest in Culex sitiens Wiedemann (95%) followed by Cx. quinquefasciatus Say (90%), Aedes aegypti (L.) (79%), Anopheles subpictus Grassi (64%), Ae. albopictus (Skuse) and Armigeres subalbatus Coquillett (62%), Cx. tritaeniorhynchus Giles (57%), Mansonia annulifera (Theobald) (46%), An. stephensi Liston (40%) and An. culicifacies Giles (36%). When fourth-instar larvae were exposed, the infection was highest in Ar. subalbatus (66%), followed by An. stephensi (52%), Cx. quinquefasciatus (47%), Ae. aegypti and An. subpictus (42%), Ae. albopictus (30%), An. culicifacies (29%), Cx. sitiens (24%), Cx. tritaeniorhynchus (19%) and Ma. annulifera (8%), with 2-45% of infected culicines surviving to adulthood. The parasitic phase of the nematode lasted 5-7 days in all the host species, yielding 1.1-3.2 parasites per II instar and 1.1-2.5 parasites per IV instar. The overall output of parasites per 100 mosquito larvae (infected + uninfected) was highest for Ae. aegypti when mosquitoes were exposed during II instar (2.53 parasites/larva) and for Ar. subalbatus when mosquitoes were exposed during IV instar (1.65/larva), and lowest for Ma. annulifera exposed during IV instar (0.09/larva). For routine laboratory culture of R. iyengari it is convenient to employ Cx. quinquefasciatus as the host yielding 90-190 parasites/100 larva.     

A new black fly isolate of Bacillus thuringiensis autoagglutinating strain highly toxic to Simulium pertinax (Kollar) (Diptera, Simuliidae) larvae

Formulations containing the entomopathogenic Bacillus thuringiensis serovar israelensis strain IPS-82 has been widely applied for mosquito control around the world. Strain IPS-82 is highly active against Aedes aegypti but less active against other well-known vectors such as Culex quinquefasciatus and Simulium spp. larvae. Eighteen strains of B. thuringiensis were isolated from Simulium pertinax larvae naturally occurring in rivers of Southeast Brazil with one demonstrating special toxic effects. Simulated field tests against S. pertinax larvae showed that the native Brazilian autoagglutinating B. thuringiensis (LFB-FIOCRUZ 1035) has an LC50 at least 25 times lower than the standard IPS-82 strain. The same bacterial preparation was also tested against Ae. aegypti larvae in laboratory trials and the LC50 values obtained with LFB-FIOCRUZ 1035 were at least three times lower than the one for the IPS 82 strain. The results indicate that this strain is more toxic than the standard B. thuringiensis serovar israelensis (H14) in the two Dipteran species tested. It is noteworthy that differences between LC50 values were more pronounced in S. pertinax larvae, the source of the original isolation.