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Biomedical subjects

H H Yap

Publications and source records attributed to H H Yap.

At least 37 records · Page 2Linked to original sources
PubMed1986

Field and laboratory observations on Coquillettidia crassipes in relation to transmission of Brugia malayi in Peninsular Malaysia.

Field observations were made on Coquillettidia crassipes during a study of Mansonia in a swamp forest ecotype in Tanjong Karang. There was an increase in abundance in July consistent with the increase in abundance of Mansonia and an increase in rainfall. The biting cycle showed a dramatic early peak during the period 1900-2000 hours. The probability of daily survival through one day for the first three gonotrophic cycles was 0.770, 0.722 and 0.759. Two of the 54 Cq. crassipes dissected were infective, with two and 25 L3 larvae of Brugia. Both subperiodic B. malayi and B. pahangi developed into L3 larvae in laboratory bred Cq. crassipes. The index of experimental infection was higher for B. pahangi. Mansonia bonneae and Ma. uniformis showed higher indices of experimental infection than Cq. crassipes for subperiodic B. malayi. It is concluded that in an endemic area with a high density of Cq. crassipes it could act as a secondary vector of Brugian filariasis.

Animals↗
PubMed1986

Field studies on the surveillance of Coquillettidia crassipes (Van der Wulp) and the isolation of a strain of Cardiofilaria in peninsular Malaysia.

Surveillance methods for Coquillettidia crassipes were studied in an open housing estate near Kuala Lumpur using three types of traps Trinidad 10 trap, modified Lard can trap and IMR trap, each baited with chicken or pigeon. All traps attracted Cq. crassipes. There was no significant difference in the catches in the three traps. There was also no significant difference between chicken and pigeon as bait. Catches at heights of 1.5, 3, 4.5 and 6 m did not show any significant difference in density. Cq. crassipes was active at night with an early peak during the first hour of the night and a minor peak between 0100 and 0200 hours. The activity of the parous and nulliparous sections of the population was similar, except that a higher proportion of the parous females was active during the second peak compared with the nulliparous females. The parous rate was 22.3%, and the probability of survival through one day for two gonotrophic cycles was 0.711 and 0.650. The infection rate for Cardiofilaria was 29 out of 1052 (2.76%) and the infective rate (L3 larvae) was 13 out of 1052 (1.24%). 48.3% of the infected Cq. crassipes had a worm burden of more than ten larvae. One of the chickens in the traps was positive for microfilariae of Cardiofilaria four weeks after exposure as bait. Laboratory bred Cq. crassipes fed on this chicken produced infective larvae in ten days, and these were inoculated into clean chickens and pigeons. Microfilariae appeared in the chickens but not in pigeons. The adult worms recovered await identification.

Animals↗
PubMed1986

Effectiveness of soap formulations containing deet and permethrin as personal protection against outdoor mosquitoes in Malaysia.

Two soap formulations, both containing 20% deet and one each containing permethrin at 0.5 and 1.0%, respectively, were applied to exposed arms and legs of volunteers as personal protection against outdoor human biting mosquitoes in six locations on Penang Island, Malaysia. The predominant mosquito species collected from these locations were Aedes albopictus, Mansonia uniformis, Culex gelidus, Anopheles lesteri and Armigeres subalbatus. Efficacy and residual effects up to 4 hours indicated good protection against these species. Reduction in mosquito landing-biting rates in treated groups ranged from 83.8 to 100.0%. At high densities, small percentages of Ma. uniformis and An. lesteri landed or bit on treated skin. Use of the soap formulations in terms of cost-effectiveness, safety and overall vector control strategy for some tropical diseases is discussed.

Animals↗
PubMed1985

Bioassays of Bacillus sphaericus (strain 1593) against mosquitoes of public health importance in Malaysia.

The pathogenicity of Bacillus sphaericus strain 1593 was tested against laboratory-reared larvae of four local species of mosquitoes of public health importance in Malaysia; Aedes aegypti, Anopheles balabacensis, Mansonia uniformis and Culex quinquefasciatus. The bacteria was shake-cultured at 28 +/- 1 degrees C for three days, using Glucose-Yeast Extract Salts medium. After which, the spores and vegetative cells were harvested and stored at 4 degrees C before use. Conditions for bioassays were mean temperature of 25 +/- 1 degrees C and relative humidity 65 +/- 5.0. Twenty third-instar larvae of each species were assayed in 90 ml of diluted spore solution. Each concentration and a control were replicated three times for each bioassay. Larval mortalities at 24 hours and 48 hours were taken and analyzed through Probit Analysis using a computer (IBM 370). LC50 values after 48 hours of exposure showed an increasing order of larval susceptibility as follows: Ae. aegypti (417.70 x 10(4)), An. balabacensis (45.84 x 10(4)), Ma. uniformis (18.23 x 10(4)) and Cx. quinquefasciatus (4.14 x 10(4) spores/ml). With the ability to kill 90% of the Cx. quinquefasciatus larvae tested with just a concentration of 10(5) spores/ml, B. sphaericus (strain 1593) has shown good potential as a biocontrol agent for this species of mosquito.

Animals↗
PubMed1984

Comparative bioassays of Tolypocladium cylindrosporum Gams (Californian strain) against four species of mosquitoes in Malaysia.

Comparative laboratory bioassays of Tolypocladium cylindrosporum, California strain (Kal) was conducted against third instar larvae of four species of mosquito, viz. Aedes aegypti, Anopheles balabacensis, Culex quinquefasciatus and Mansonia uniformis in Malaysia. Of the four mosquito species tested, Ma. uniformis was found to be the most susceptible, followed by Cx. quinquefasciatus, An. balabacensis and Ae. aegypti, in a decreasing order. The LC50 values for Ma. uniformis, Cx. quinquefasciatus, An. balabacensis and Ae. aegypti after four days of exposure were 1.18 X 10(4), 2.02 X 10(5), 4.76 X 10(5) and 1.84 X 10(7) spores per ml test media, respectively. The high sensitivity of Ma. uniformis and its longer life cycle seems to indicate that T. cylindrosporum Kal has good potential as a biocontrol agent for this species of mosquito. But, for Ae. aegypti, this fungus appears to be less effective.

Aedes↗
PubMed1982

Comparative bioassays of Bacillus thuringiensis H-14 formulations against four species of mosquitoes in Malaysia.

Comparative laboratory bioassays of three formulations of Bacillus thuringiensis H-14 (IPS-78, San 402-I and Bactimos) were conducted against late 3rd/early 4th instar larvae of four species of mosquito, viz., Aedes aegypti, Culex quinquefasciatus, Anopheles balabacensis and Mansonia (Mansonioides) indiana, in Malaysia. From the average response of the mosquito larvae to the three formulations of B. thuringiensis H-14, Ae. aegypti was found to be most susceptible, followed by Cx. quinquefasciatus, An. balabacensis and M. (M.) indiana in decreasing order. The LC50 values for Ae. aegypti, Cx. quinquefasciatus, An. balabacensis and M. (M.) indiana after a 48-hour exposure to IPS-78 formulation were 50.9, 129.3, 117.8 and 169.6 International Toxic Unit (ITU) Ae. ae./l; to San 402-I formulation were 54.6, 223.1, 405.1 and 177.6 ITU Ae. ae/l and to Bactimos formulation were 57.2, 175.7, 35.6 and 514.5 ITU Ae. ae./l respectively. The efficacy of the bacterial product was also found to be determined by its formulation in relation to the feeding and resting habits of the mosquito larvae. No delayed pupation or emergence was observed on the larvae exposed to B. thuringiensis H-14 at sub-lethal concentrations.

Animals↗
PubMed1982

Laboratory and field tests of temephos (AbateR) on mosquito larvae and non-target organisms in rice fields in Malaysia.

The toxic effects of Abate (temephos) on mosquito larvae and non-target organisms were studied in the rice-field and in the laboratory. In the laboratory tests, Culex tritaeniorhychus larvae and cladoceran zooplanktons (predominantly Diaphanosoma and Moinodaphnia species) were found to be highly susceptible to Abate with LC50 values of 0.27 and less than 0.10 parts per billion respectively. Other non-target species in decreasing degree of susceptibility to Abate were copepods (Tropodiaptomus spp.), Aplocheilus panchax and Tubifex worms. In field study, Abate at concentrations 60, 100 and 200 gm hectare-1 is effective in maintaining the rice-fields free of Anopheles and Culex mosquitoes for at least 2 days. No mortality was observed for Aplocheilus panchax and Tubifex worms at the above concentrations; nevertheless, populations of cladoceran zooplanktons and copepods were reduced up to seven days posttreatment.

Animals↗
PubMed1977

Evaluation of DursbanR and Dowco 214 as mosquito larvicides in rice-fields.

Emulsifiable concentrates of DursbanR (chlorpyrifos) and Dowco 214 (chlorpyrifos-methyl) were tested as mosquito larvicides using Hudson knapsack sprayers on small plots of rice-fields on Penang Island. The mosquitoes found in these rice-fields are predominantly Anopheles campestris and Culex tritaeniorhynchus. At dosages of 14, 28 and 56 gm hectare-1, Dursban is effective in maintaining the rice-fields free of Anopheles larvae for at least 2, 3 and 7 days respectively. Dowco 214 at 56 gm hectare-1 is able to keep the fields free of all mosquito larvae for at least 2 days.

Animals↗
PubMed1976

Laboratory insecticide susceptibility tests against Mansonia larvae.

Insecticides Abate, DDT, Dowco-214, Dursban, fenitrothion, fenthion, gamma-HCH, and malathion were tested against the field collected fourth instars larvae of Mansonia from Penang Island, Malaysia. The larvae appeared to be highly susceptible to Dursban and Abate with LC50 values of 1.54 and 1.92 parts per billion respectively. Other chemicals, in decreasing degree of effectiveness, were gamma-HCH, fenthion, P,P'-DDT, Dowco-214, fenithrothion and malathion. The potential use of these chemicals in Mansonia control was discussed. A simple method for collecting and testing Mansonia larvae was also described.

Animals↗
PubMed1975

Distribution of Aedes aegypti (Linnaeus) and Aedes albopictus (Skuse) in small towns and villages of Penang Island, Malaysia--an ovitrap survey.

An ovitrap survey was carried out in April and May of 1975 at twenty-one locations scattered throughout Penang Island excluding the City of Georgetown. The results showed the ubiquitous presence of Ae. albopictus. Ae. aegypti was recorded only in Tanjung Tokong Lama, an area adjacent to the City of Georgetown. In the survey, Ae. albopictus females were found to prefer the outdoor ovitraps than indoor ones. The effectiveness of ovitrap in Aedes survey was discussed.

Aedes↗