Biomedical subjects

M S Mulla

Publications and source records attributed to M S Mulla.

At least 37 records · Page 2Linked to original sources

PubMed1997

Selection-dependent trends of autogeny and blood feeding in an autogenous strain of Culex tarsalis (Diptera:Culicidae).

During successive en masse selection of autogeny in Culex tarsalis from parental to 20th generation, the autogenous oviposition capacity changed as follows: mean number of egg rafts/female and mean number of eggs/female increased significantly, from 0.11 to 0.56 and from 6.2 to 20.2, respectively; the mean size of the egg rafts decreased significantly, from 56.2 to 36 eggs/raft; autogeny rates increased significantly, from 18.6 to 65.2%; mean number of autogenous follicles/female decreased significantly, from 57.4 to 34; the hatching rate of autogenous egg rafts reduced significantly, from 88.3 to 75.4%; and the feeding rates of the females on a blood meal source during the 7th day postemergence increased significantly, from 62.8 to 71.1%. The autogeny rate determined by ovarian dissection was higher than that indicated by actual oviposition. As the age of females increased during the observed 10-day oviposition period, the mean number of egg rafts/female, the mean number of eggs/female, and the mean number of eggs/raft decreased successively, and scattered "light color" egg rafts became more common. Successive en masse selection enhanced autogeny and strengthened the bloodfeeding tendency in this facultative autogenous species.

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PubMed1997

Field trials with Bacillus sphaericus formulations against polluted water mosquitoes in a suburban area of Bangkok, Thailand.

Two newly developed Bacillus sphaericus larvicidal formulations, VectoLex CG (corncob granules) and VectoLex WDG (water dispersible granules), were tested against Culex quinquefasciatus larvae in 4 highly polluted breeding sites in Thailand. VectoLex CG, applied at rates of 0.5-2 g/m2, gave satisfactory to complete control of late-instar larvae and pupae for up to 4 wk after treatment. The VectoLex WDG, which had higher potency and was applied at rates of 0.1-0.5 g/m2, gave satisfactory control for 1-4 wk after treatment. Among the factors influencing longevity of control were dosage of a given formulation, precipitation, and flooding of the treated sites; the latter had the greatest impact. Presence of larvivorous fish did not seem to influence larval populations because there were heavy populations of mosquito larvae present in the test sites in the presence of moderate numbers of fish before the application of B. sphaericus treatments.

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PubMed1997

Physiological aspects of autogeny in Culex tarsalis (Diptera: Culicidae): influences of sugar-feeding, mating, body weight, and wing length.

Sugar feeding and mating promoted the expression of autogeny in Culex tarsalis. In sugar-fed cohorts fed 5, 10, and 20% sucrose solution, the mean number of egg rafts/female, mean number of eggs/raft, mean number of eggs/female, mean number of autogenous follicles/female, and the autogeny rate were all significantly greater than those in sugar-deprived cohorts. There were no significant differences in these parameters among the sugar-fed groups of 5, 10, and 20%. Similarly, magnitudes of the parameters mentioned above in female-male cohorts were significantly higher than those in female-alone cohorts. There was no difference in the hatching rate of the autogenous egg rafts in the cohorts fed on different sucrose solutions and the female-male cohorts, while it was 0 in male-deprived cohorts. There were positive correlations between mean emergence weight and mean number of autogenous eggs/female (r2 = 0.69), mean emergence weight and mean number of autogenous follicles/female (r2 = 0.75), mean wing length and mean number of autogenous eggs/female (r2 = 0.64), and mean wing length and mean number of autogenous follicles/female (r2 = 0.63). The regression analysis of the data indicated that females with emergence weights < 1.92 mg could not oviposit autogenously, and those with emergence weights < 1.89 mg could not develop the ovaries autogenously. Females with wing lengths < 2.89 mm could not oviposit autogenously and those with the wing length of < 2.83 mm could not develop the ovaries autogenously. The coefficient of correlation between emergence weight and autogenous follicles/female was greater than that between emerging weight and autogenous eggs/female. The coefficients of correlation between emergence weight and autogeny were greater than that between wing length and autogeny. Therefore, autogenous follicles/female is a more accurate parameter to describe autogeny expression level than autogenous eggs/female because oviposition is affected by other factors, and emergence weight is a more important factor determining autogeny expression than wing length.

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PubMed1996

Effect of tadpole shrimp, Triops longicaudatus, (Notostraca: Triopsidae), on the efficacy of the microbial control agent Bacillus thuringiensis var. israelensis in experimental microcosms.

Laboratory bioassays using Culex quinquefasciatus larvae evaluated the effect of tadpole shrimp on the persistence of Bacillus thuringiensis var. israelensis (B.t.i.) in water collected from the surface of field microcosms. Time elapsed since B.t.i. treatment, as well as presence or absence of soil and tadpole shrimp, affected B.t.i. persistence at the water surface in 15- and 30-cm total depths. The presence of tadpole shrimp slowed the natural decline in B.t.i. effectiveness over time, but this effect was depressed when soil was present. Tadpole shrimp foraged throughout the water column and stirred up the substrate, keeping more particles in suspension at the surface than in microcosms with no shrimp, in microcosms with water depths of 15 and 30 cm.

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PubMed1996

Diel patterns of oviposition and influence of agitated water surface in Chironomus anonymus (Diptera:Chironomidae).

A series of experiments was carried out in a 0.5-ha lake at Portola Country Club, Palm Desert, CA, to study the oviposition habits of Chironomus anonymus. Egg masses were collected by floatable polypropylene ropes attached to the 1.5-m-long stakes placed in the lake. In the diel experiment, ropes were changed every 2 h to determine the preferred oviposit on periods of C. anonymus. The peak of oviposition was between 1900 and 2100 h. For the interruption of oviposition experiment, ropes were placed in the still and agitated portions of the lake for 24 h. A significantly higher number of egg masses, according to applied t-test, was collected from the ropes placed in the still portion of the lake.

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PubMed1996

Cross-resistance to Bacillus sphaericus strains in Culex quinquefasciatus.

Laboratory and field-collected strains of Culex quinquefasciatus that were selected with Bacillus sphaericus strain 2362 in the laboratory for about 100 generations and attained 37- and 31-fold resistance, respectively, did not show marked cross-resistance to Bacillus thuringiensis spp. israelensis; only 2-3-fold tolerance was noted. However, they showed significant levels of cross-resistance to strains 1593 (6-22-fold) and 2297 (4-12-fold) of B. sphaericus. Possible mechanisms and management implications are discussed.

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PubMed1996

Optimal conditions for rearing the tadpole shrimp, Triops longicaudatus (Notostraca:Triopsidae), a biological control agent against mosquitoes.

Tadpole shrimp (TPS) were reared at 15, 20, 25, and 30 degrees C in the laboratory. Size of TPS was temperature and age dependent with more rapid development at warmer temperatures. Survivorship was inversely related to rearing temperature. Mean age at death was 24.2, 19.2, 14.3, and 11.8 days at 15, 20, 25, and 30 degrees C, respectively. Rearing temperature (excluding 15 degrees C) did not affect lifetime fecundity, but larger TPS laid more eggs than smaller ones. Tadpole shrimp began ovipositing earlier at higher temperatures, and at a smaller size than their counterparts in lower temperatures. Mean age at reproductive maturity was 18.8, 13.1, and 10.2 days and mean carapace length was 10.8, 11.0, and 10.3 at 20, 25, and 30 degrees C, respectively. Embryogenesis required a minimum of 3 days for completion. Hatching rates during the first hydration decreased with increasing egg batch number produced by individuals, ranging from a mean of 74% for the first batch to 31% for the 5th batch. Cumulative hatching rates of eggs after 2 hydrations were consistent across temperatures and egg batches (79 +/- 2%).

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PubMed1995

Effects of organic enrichment on temporal distribution and abundance of culicine egg rafts.

The effect of organic enrichment of the larval habitat on mosquito oviposition was determined in 2 replicated field experiments. In the first study, Culex stigmatosoma and Culex quinque-fasciatus oviposition (as measured by the number of early instar larvae) reached a maximum peak soon after flooding and then declined to a substantially lower equilibrium level. A group of ponds that later received supplemental organic matter had a significant increase in oviposition soon after the additional organic matter was added. In the second experiment, a similar ovipositional pattern was noted by the sampling of egg rafts along transects and determining larval abundance by the dipping technique. In the second experiment a mixture of Culex stigmatosoma and Culex tarsalis larvae was collected.

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PubMed1995

The future of insect growth regulators in vector control.

Insect growth regulators (IGRs) are diverse groups of chemical compounds that are highly active against larvae of mosquitoes and other insects. The IGRs in general have a good margin of safety to most nontarget biota including invertebrates, fish, birds, and other wildlife. They are also relatively safe to man and domestic animals. The IGR compounds do not induce quick mortality in the preimaginal stages treated. Mortality occurs many days later after treatment. This is indeed a desirable feature of a control agent because larvae of mosquitoes and other vectors are an important source of food for fish and wildlife. On account of these advantages of IGRs and the high level of activity against target species, it is likely that IGRs will play an important role in vector control programs in the future.

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PubMed1995

Oviposition responses of Culex tarsalis and Culex quinquefasciatus to aged Bermuda grass infusions.

Fermented infusions of organic matter are commonly used as baits in traps for gravid female mosquitoes. However, infusions are dynamic, and their effects on mosquito oviposition as their chemical and microbial constituents change over time are not well documented. Bermuda grass infusion fermented for periods of 0-63 days was stimulatory to gravid Culex quinquefasciatus. In contrast, only 5-25-day-old infusion was stimulatory to Culex tarsalis. Standard-aged infusion (7 days old) was as effective or better than infusion of any other age for Cx. tarsalis, whereas Cx. quinquefasciatus exhibited a distinct preference for 2-4-wk-old infusion. The results are discussed in terms of mosquito species' oviposition site preferences and in terms of mosquito surveillance programs.

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PubMed1995

Mode of existence and seasonality of midge larvae (Diptera: Chironomidae) in man-made lakes in the Coachella Valley, southern California.

Over the past 2 decades, numerous man-made ponds and lakes constructed in country clubs and on golf courses in the Coachella Valley have become ideal habitats for various chironomid species. Large numbers of adult midges emerging from these water bodies pose nuisance and economic problems. During 1992 and 1993 we initiated comprehensive studies on the nature and scope of the nuisance midge problem in the valley. We sampled on a biweekly basis 2 lakes supplied with well water, 2 supplied with tertiary effluent water, and one supplied with a mixture of these 2 sources, to determine the midge larval fauna and the mode of existence, seasonal abundance, and population trends of these midges. Climbers, clingers, portable sand tube builders, and tube builders on plants predominated in well-water habitats with submerged vegetation and detritus bottoms. Tube builders and burrowers predominated in the tertiary water, which characteristically had a detritus bottom, devoid of vegetation. Habitats holding a mixture of the 2 water types with sandy bottoms supported midge larvae known to be sprawlers.

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PubMed1994

Protein hydrolysates and associated bacterial contaminants as oviposition attractants for the mosquito Culex quinquefasciatus.

Six protein or protein hydrolysate solutions were tested for activity as attractants for ovipositing Culex quinquefasciatus mosquitoes in the laboratory. Four of these solutions (egg albumin, lactalbumin hydrolysate, casein hydrolysate and yeast hydrolysate) were attractive to ovipositing females at varying concentrations, when compared to distilled water controls. Soy hydrolysate was repellent at 1%, but not significantly attractive or repellent at lower concentrations. 'Nulure', a tephritid fly bait containing protein hydrolysate, also had no significant effect on oviposition behaviour. Gravid females mostly oviposited within the first 4 h of the scotophase, regardless of the presence or absence of an oviposition attractant. Lactalbumin hydrolysate 1% solution, with or without 0.1% neomycin antibiotic, was attractive to Cx quinquefasciatus. This effect was reduced by the presence of neomycin which, alone, had no effect on oviposition. Hence both lactalbumin hydrolysate and bacterial contaminants were shown to be attractive to gravid Cx quinquefasciatus.

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PubMed1994

Mosquito control then, now, and in the future.

This is a memorial lecture honoring the late Professor Stanley B. Freeborn of the University of California. In the spirit of his life-long academic and research interests in mosquitoes and mosquito-borne diseases, I am presenting here the evolution of vector control technology, especially that pertaining to mosquitoes and mosquito-borne diseases during the 20th century. Vector control technology in the first half of this century was relatively simple, utilizing source reduction, larvivorous fish, petroleum hydrocarbon oils, and some simple synthetic and botanical materials. During the 2nd half of this century, however, various classes of synthetic organic chemicals, improved petroleum oil formulations, insect growth regulators, synthetic pyrethroids, and microbial control agents were developed and employed in mosquito control and control of other disease-vectoring insects. Among these groups of control agents, petroleum oil formulations have endured to be used through the whole century. It is likely that petroleum oil formulations, insect growth regulators, and microbial control agents will provide the main thrust against vectors at least during the first quarter of the 21st century. It is also possible that effective tools through the development of vaccines and molecular entomology techniques might become available for the control of vectors and vector-borne diseases during this period of the 21st century.

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PubMed1994

Interaction of the Culex quinquefasciatus egg raft pheromone with a natural chemical associated with oviposition sites.

In laboratory bioassays, gravid Culex quinquefasciatus mosquitoes were strongly attracted and or stimulated to oviposit by a habitat-derived chemical cue, 3-methylindole, at several concentrations ranging from 0.01 to 1 microgram/liter in water. At concentrations above 10 micrograms/liter, 3-methylindole became repellent or deterrent. Responses to the known egg raft pheromone, 6-acetoxy-5-hexadecanolide, were much weaker and were relatively constant above a threshold dosage of about 0.1 microgram. Responses to blends of a fixed amount of the pheromone with variable doses of 3-methylindole were shown to be additive rather than synergistic.

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PubMed1993

Spatial and circadian oviposition patterns in an urban population of Culex quinquefasciatus.

A transect of infusion-baited oviposition tubs was used at the Orange County (CA) Vector Control District facility to determine the circadian periodicity and the influence of urban habitat factors, such as buildings, ornamental plantings, and mercury vapor lights on Culex quinquefasciatus oviposition activity. The peak oviposition activity occurred during the first 2 h after sunset. Nearly 80% of egg rafts deposited were laid within the first 4 h after sunset and no morning ovipositional peak was detected. Urban and physical habitat factors considered had no effect on tub selection by ovipositing females. Linear analysis indicated that eggs were laid randomly among tubs. Eighty-eight percent of the rafts collected were Cx. quinquefasciatus. The remaining egg rafts were laid by Culex tarsalis, Culex stigmatosoma, and Culieseta incidens.

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PubMed1993

Effect of the insect growth regulator methoprene on the ovipositional behavior of Aedes aegypti and Culex quinquefasciatus.

Laboratory and field tests were conducted to determine the attractiveness of the insect growth regulator methoprene to ovipositing mosquitoes when presented at concentrations used in mosquito control programs. Laboratory experiments indicated that ovipositing Culex quinquefasciatus and Aedes aegypti were not attracted to methoprene. In field experiments, Culex stigmatosoma and Cx. quinquefasciatus larval dip counts in experimental ponds treated with methoprene briquets were not significantly different from untreated control ponds. Water taken from these methoprene-treated ponds was not attractive when compared with water taken from untreated ponds to ovipositing Cx. quinquefasciatus in laboratory experiments. These studies provide strong evidence that methoprene is not attractive to ovipositing mosquitoes at concentrations within the range of field applications.

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PubMed1992

Effect of drying period and soil moisture on egg hatch of the tadpole shrimp (Notostraca: Triopsidae).

Tadpole shrimp (Triops spp.) are potential biological control agents against larval mosquitoes in temporary ponds and flood-irrigated fields. In some rice field situations, however, they may become pests that uproot and eat young rice plants. In cursory observations, it has been reported that tadpole shrimp eggs do not readily hatch on flooding when the soil or substrate containing eggs is moist before flooding. The relationship between drying (moisture content) of soil and tadpole shrimp hatch was determined in studies conducted in mesocosms at the University of California Aquatic and Vector Control Research facilities at Riverside and at Oasis in the Coachella Valley of southern California. In laboratory hatching trials, an increase in hatch of Triops longicaudatus (LeConte) with declining soil moisture content was demonstrated (t = 8.4, P less than 0.001; r2 = 0.76). In field trials in mesocosms at Riverside, egg hatch increased with increased drying period and declining soil moisture content (G = 29.8, P less than 0.01). No hatch of eggs occurred after 3 d of drying, when soil moisture content was high, but a high level of hatching occurred after 7 and 14 d of drying, when soil moisture declined to low levels. At Oasis, soil moisture did not decrease with drying time because of porous soil and capillary action of water from adjacent flooded mesocosms and thick vegetation covering the pond bottoms. Therefore, hatch rates at Oasis were not associated with the length of the drying period (G = 35, P greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed1992

Identification of oviposition attractants for Culex quinquefasciatus from fermented Bermuda grass infusions.

Compounds which attract and stimulate oviposition by gravid Culex quinquefasciatus were isolated and identified from a fermented Bermuda grass infusion. The neutral portion of the ether extract of the aqueous infusion contained the stimulatory materials. Fractionation by liquid chromatography yielded an active fraction containing phenol, 4-methylphenol, 4-ethylphenol, indole and 3-methylindole. A blend of the 5 compounds strongly stimulated oviposition, as did blends of any 4 of them. Bioassays with individual compounds showed that only 3-methylindole consistently induced oviposition, in concentrations spanning 5 orders of magnitude.

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