A laboratory simulation study on suppression of resistance genes by differential exposures to an insecticide in Anopheles stephensi Liston population

Background & objectives

: Insecticide applied at optimum dosage and coverage delays the development of resistance in disease vectors. The study was aimed to test the hypothesis whether decrease in exposure to insecticide leads to decrease in selection of insecticide resistance in mosquitoes. The mosquitoes were variably exposed to insecticide in the laboratory by simulating the variations in insecticide sprays applied in the field.

Methods

: The study was carried out on DDT resistant adults of Anopheles stephensi. Mosquitoes were differentially exposed to impregnated papers of DDT (4%), that were differentially masked to 25, 50, and 75% area with an unimpregnated Whatman No.1 filter paper, and to a positive control without any masking, i.e. 100% exposure area. The study was conducted for five generations and at each generation mosquitoes were exposed to differentially masked impregnated papers, and percent mortality was calculated.

Results

: The observed survival rate in differential exposures was more with the increase in heterozygous genotype resistance-susuceptible (RS) frequency. Resistant gene frequency with differential exposures (25 to 75%) was in the range of 0.38-0.54 for the F₀ generation, which increased to 0.84-0.93 for the F₄ generation. In 100% exposure it was 0.18 in F₀ generation, which increased to 0.58 in the F₄ generation. The resistant gene frequencies in the population showed increasing trend with decrease in exposure in contrast to complete exposure.

Interpretation & conclusion

: Variable simulated exposures resulted in precipitation of increased resistance while complete exposure resulted in lower levels of resistance, signifying the importance of optimum dosage and coverage in the indoor residual spray in delaying/avoiding the development of insecticide resistance in the disease vectors.

Malaria vector Anopheles culicifacies sibling species differentiation using egg morphometry and morphology

Background

The malaria vector Anopheles culicifacies (sensu lato) is an important malaria vector in Southeast Asia which comprises of five sibling species namely A, B, C, D and E. However, only a few forms have been identified as malaria vectors in various endemic countries. Currently, for the first time egg morphometry and morphology has been used to differentiate the three known vector sibling species of Anopheles culicifacies collected from malaria endemic Madhya Pradesh state of central India.

Methods

The adult An. culicifacies (s.l.) was collected from five districts using standard mosquito collection methods. Adult female mosquitoes were allowed to lay eggs individually. The emerged mosquitoes were identified using allele specific polymerase chain reaction (AS-PCR) to sibling species. Eggs of sibling species A, D and E were studied using scanning electron microscopy (SEM) for morphometric and morphological characteristics.

Results

Currently AS-PCR identified four known sibling species (B, C, D and E) of An. culicifacies in the study area. The surface morphology and morphometric attributes of the sibling species A, D and E eggs considerably differed from each other. An. culicifacies E had a narrow deck as compared to A and D, while An. culicifacies A had a bigger micropyle with 6–7 sectors as compared to D and E that had 6 sectors. An. culicifacies D had the smallest float (the structure present on sides of the egg surface in which air is filled that help in floating) and the number of ribs was also fewer than for An. culicifacies A and E.

Conclusions

The present study provides the first evidence that in addition to PCR assay, sibling species of An. culicifacies can also be differentiated using morphological and morphometric characteristics of the egg stage. The results also advocate that the sibling species of An. culicifacies are morphologically dissimilar and can be resolved using advanced microscopy.

Chlorfenapyr: irritant effect compared to other insecticides and its intrinsic toxicity in multiple-insecticide-susceptible and -resistant Anopheles stephensi (Diptera: Culicidae)

BACKGROUND & OBJECTIVES

For effective management of vector resistance there is a need for new insecticide molecules with novel modes of action. For desired toxic effect of an insecticide, apart from other behavioural aspects, toxicity and chemical nature of the molecule are important that may cause irritability in the mosquito to the insecticide affecting the uptake. In this study, a pyrrole class insecticide, chlorfenapyr (a late acting insecticide) was tested for its irritability against multiple-insecticide-susceptible and -resistant strains of Anopheles stephensi Liston 1901 (Diptera: Culicidae).

METHODS

Studies were conducted to assess the irritability due to chlorfenapyr, DDT, malathion, deltamethrin and permethrin and intrinsic toxicity of chlorfenapyr in multiple-insecticide-susceptible and -resistant laboratory strains of An. stephensi following standard WHO methods.

RESULTS

Chlorfenapyr molecule has shown least irritant effect against susceptible and resistant strains among all the insecticides tested allowing more landing time to the vector species on the impregnated surfaces to pick-up lethal dose.

CONCLUSION

Chlorfenapyr could be an ideal insecticide for management of multiple-insecticide-resistance including pyrethroids.

Olfaction in Asian tiger mosquito Aedes albopictus: flight orientation response to certain saturated carboxylic acids in human skin emanations

The flight orientation response of nonblood-fed and hungry Aedes albopictus females was studied in a Y-tube olfactometer at 10(-6) to 10(-2) g odor plumes of saturated carboxylic acids (C1-C20), in which C2-C18 were the main constituents of human skin emanations. Thirteen acids viz C1, C2, C3, C5, C6, C8 C9, C10, C12, C14, C16, C18, and C20 showed attractance at odor plumes ranging from 10(-5) to 10(-3) g doses, while five acids viz C4, C7, C11, C15, and C19 showed repellence at 10(-4) to 10(-2) g to test mosquitoes. Tridecanoic acid (C13) showed attractance only at 10(-4) g dose while higher doses caused repellence. Dose-dependent reversal of orientation behavior from attractance to repellence was observed at 10(-2) g plumes of C5, C9, C10, C13, C17, C19, and C20 acids. The outcome of the study will help in the identification of odoriferous acids as potential attractants, repellents, or attraction inhibitors, which may find their application in the repellent formulations and odor-baited traps for surveillance and control of mosquitoes.

Variations in life tables of geographically isolated strains of the mosquito Culex quinquefasciatus

Variations in the life tables and other biological attributes of four strains of Culex quinquefasciatus Say (Diptera: Culicidae) from geographically isolated regions of India that had been reared to the fifth generation in the laboratory were assessed under a standardized rearing regime under constant laboratory conditions. Two strains from arid habitats [Jodhpur (JD) and Bikaner (BKN)], one from a semi-arid inland habitat [Bathinda (BTH)], one from a semi-arid coastal habitat [Jamnagar (JMN)] and a standard laboratory strain (LAB) were compared. Horizontal life-table parameters were measured for each strain. Egg mortality ranged from 4.4% (JD and BTH) to 19.5% (BKN). The lowest rate of adult emergence and highest female : male ratio were found in BKN, and the highest rate of adult emergence and lowest female : male ratio were recorded in BTH. The egg-hatching period was longest in BTH and shortest in LAB. The duration from oviposition to adult emergence was longest in JD and shortest in LAB. Females lived longer than males in all strains. The net reproductive rates (R(0) ) of all field-derived strains (122.9-162.2) differed significantly between strains and were significantly greater than that of LAB (107.6). Similarly, both the intrinsic rate of increase (r(m) ) and finite rate of increase (λ) were found to be lower in LAB than in the field strains, but the mean generation time (T) and doubling time (DT) were longest in LAB. For several life-table attributes, JD and BTH clustered together and were more similar to JMN than to BKN and LAB. The results indicate that BTH, BKN and JD can be characterized as r-strategists, more so than JMN. Overall fecundity increased with age. Differences in annual temperature ranges and mean annual rainfall between locations were positively correlated (r = 0.46-0.97) with egg production, female life expectancy, R(0) , r(m) , λ and T. The results suggest that strains of Cx. quinquefasciatus from different geographical areas with contrasting habitats vary in their survival and reproductive strategies accordingly.

Variation in morphology and morphometrics of eggs of Culex quinquefasciatus mosquitoes from different ecological regions of India

Variation in egg surface morphology and morphometrics of Culex quinquefasciatus mosquitoes of the Jodhpur, Bikaner, Jamnagar, and Bathinda strains were correlated with geographical distribution in different ecological regions of India. We report the geographic variation in Cx. quinquefasciatus based on 44 attributes of micropylar and conical-shaped regions of eggs, including micropylar apparatus (corolla, disc, and mound), micropylar tubercles, and the exochorionic tubercle, pores, and network in anterior, middle, and posterior regions. No remarkable differences were observed in the surface morphology of eggs of these strains except the absence of small tubercles in the anterior and middle region of the JMN strain. However, a statistical analysis indicated significant morphometric variations in 66% of the attributes of the eggs. The cluster analysis of all egg attributes showed that the JD, BKN, and BTH strains are closer to each other than the JMN strain. The positive correlation (r = 0.95) also indicated an effect of geographical distribution on morphometry of various egg attributes of these strains. The present study suggests that ecological variation may have affected the morphometric attributes of the egg of four strains of Cx. quinquefasciatus from different geographical areas.

Mediation of oviposition responses in the malaria mosquito Anopheles stephensi Liston by certain fatty acid esters

The chemical factors involved in oviposition site selection by mosquitoes have become the focus of interest in recent years, and considerable attention is paid to the chemical cues influencing mosquito oviposition. Studies on synthetic oviposition attractants/repellents of long-chain fatty acid esters against Anopheles stephensi are limited. Screening and identification of chemicals which potentially attract/repel the gravid females to/or from oviposition site could be exploited for eco-friendly mosquito management strategies. The ester compounds demonstrated their ability to repel and attract the gravid A. stephensi females in the treated substrates. Significant level of concentration-dependent negative oviposition response of mosquitoes to octadecyl propanoate, heptadecyl butanoate, hexadecyl pentanoate, and tetradecyl heptanoate were observed. In contrast, decyl undecanoate, nonyl dodecanoate, pentyl hexadecanoate, and propyl octadecanoate elicited concentration-dependent positive oviposition responses from the gravid mosquitoes. Forcing a female to retain her eggs due to unavailability of a suitable oviposition site and attracting them to lay the eggs in a baited ovitraps shall ensure effective control of mosquito breeding and population buildup because the oviposition bioassay target the most susceptible stage of an insect life cycle. Treating relatively smaller natural breeding sites with an effective repellent and placing ovitraps containing an attractant in combination with insect-growth regulator (IGR)/insecticide would be a promising method of mosquito management.

Subjects with Impaired Glucose Tolerance Exhibit a High Degree of Tolerance to Honey

The present study compared the relative tolerance to honey and glucose of subjects with impaired glucose tolerance or mild diabetes. Thirty individuals 35-60 years old with a proven parental (mother or father) history of type II diabetes mellitus were subjected simultaneously to an oral glucose tolerance test (GTT) and a honey tolerance test (HTT). Glucose tolerance was found to be impaired in 24 subjects, while six of the subjects were diagnosed as mildly diabetic. All subjects with impaired glucose tolerance exhibited significantly lower plasma glucose concentrations after consumption of honey at all time points of the HTT in comparison to the GTT. The plasma glucose levels in response to honey peaked at 30-60 minutes and showed a rapid decline as compared to that to glucose. Significantly, the high degree of tolerance to honey was recorded in subjects with diabetes as well, indicating a lower glycemic index of honey. Thus, it is evident from the present investigation that honey may prove to be a valuable sugar substitute for subjects with impaired glucose tolerance or mild diabetes.

Profile of burn injury in steel industry

Among the industrial workers of Bokaro Steel Plant 270 cases of burn injury were studied to streamline the cases from the site of accident, to find out the different causes of burn accident and to evaluate the result of specific management. After first-aid and resuscitating at the casualty department they were treated in intensive burn unit. The most vulnerable age for burn injury were the patients of 21-30 years. Maximum number of cases were seen due to electrical flash (78 cases or 28.9%) and slag burn (70 cases or 25.9%). Flame burn (39 cases or 14.4%), electrical contact (30 cases or 11.1%), gaseous burn (20 cases or 7.4%), scald (18 cases or 6.7%) and chemical burn (15 cases or 5.6%) were accounting for the rest. Adequate safety education to young employees, prompt transport to hospital, nursing in isolated area and early excision of eschar reduced the mortality and morbidity of burn injury.

Amylase activity in the alimentary tract and salivary glands of Periplaneta americana L

The optimum conditions for amylase activity and the distribution of the enzyme in the salivary glands and various gut regions were investigated. Maximum activity of the enzyme was observed at 7.0 pH and 50 degrees C temperature and the activity increased with increasing time period, and enzyme and substrate concentrations. Amylase from the salivary glands was found to be exceptionally potent and the enzyme concentration decreased from the anterior to the posterior part of the gut in well-fed cockroaches. The findings are discussed with regard to the source of amylase synthesis.

POLAROGRAPHIC DETERMINATION OF THE DISSOCIATION CONSTANT OF THE SULPHYDRYL GROUP AND DIFFUSION COEFFICIENT MEASUREMENTS OF THIOMALIC ACID

Polarographic study of thiomalic acid has been made in the pH range 1–12.5 using Britton–Robinson buffer at 30°. The half-wave potential [Formula: see text] values have been used to determine the pK3 (SH) value of the acid (pK3 = 10.55).The diffusion current obtained in these experiments has been utilized to calculate the diffusion coefficients of the different charged species of thiomalic acid. The values thus obtained for the respective species are H3A = 1.20 × 10−5 cm2/sec; H2A− = 1.16 × 10−5 cm2/sec; HA−− = 1.08 × 10−5 cm2/sec; and A−−− = 7.67 × 10−6 cm2/sec.The standard potential of the reaction[Formula: see text]has been calculated as +0.266 volt vs. N.H.E.