Field Evaluation of Indoor Thermal Fog and Ultra-Low Volume Applications For Control of Aedes aegypti in Thailand.

Efficacies of a handheld thermal fogger (Patriot™) and a backpack ultra-low volume (ULV) sprayer (Twister™) with combinations of 2 different adulticides (pyrethrin, deltamethrin) and an insect growth regulator (pyriproxyfen) were field-tested and compared for their impact on reducing indoor Aedes aegypti populations in Thailand. The effectiveness of the indoor space sprays was evaluated by sampling the natural Ae. aegypti population in houses and determining their physiological status, by monitoring mortality of sentinel caged mosquitoes (AFRIMS strain) and by assessing larval mortality in laboratory bioassays using water exposed to the spray. A total of 14,742 Ae. aegypti were collected from Biogents Sentinel traps in this study. The combination of ULD® BP-300 (3% pyrethrin) and NyGuard® (10% pyriproxyfen) sprayed either by the Patriot or Twister significantly reduced some Ae. aegypti populations up to 20 days postspray relative to the control clusters. The addition of pyriproxyfen to the adulticide extended how long household mosquito populations were suppressed. In 2 of the 4 products being compared, the Twister resulted in higher mortality of caged mosquitoes compared with the Patriot. However, neither machine was able to achieve high mortality among Ae. aegypti placed in hidden (protected) cages. The larval bioassay results demonstrated that the Twister ULV provided better adult emergence inhibition than the Patriot (thermal fogger), likely due to larger droplet size.

Spatial and temporal patterns in the recovery of Aedes aegypti (Diptera: Culicidae) populations after insecticide treatment.

Given that tools for dengue emergency control are limited, continuous evaluation of the effectiveness of insecticide applications in the field is of utmost importance. Such studies will provide a sound basis for defining spraying schemes for public health authorities in dengue-affected countries. In this article, we address the following research questions: How do different space spraying strategies affect Aedes aegypti (L.) (Diptera: Culicidae) populations in both space and time? More specifically, how well are these mosquitoes killed, and how quickly do their populations recover and from where? Field trials were carried out with ultralow volume sprayers in Kamphaeng Phet province, Thailand, with a pyrethrin mixture that was applied 1) indoors only, 2) indoors plus outdoors, 3) indoors with a doubled spraying time, and 4) indoors with doubled spraying time plus outdoors. We found that within 7 d, Ae. aegypti populations recovered to approximately 50% of their original numbers. Spraying the outdoor area and doubling the time sprayed per room only had a significant impact on mosquito numbers 1 d after spraying. Two and 7 d after spraying, these effects were no longer detected. By investigating the spatial arrangement of Ae. aegypti numbers, we found that during the first 2 d after spraying immigration from untreated areas extended approximately 15 m into the sprayed area, whereas after 7 d this effect extended up to 50 m. Results are discussed in relation to ongoing dengue control efforts in Thailand.

Metaphase karyotypes of Anopheles of Thailand and Southeast Asia. VI. The Pyretophorus and the Neomyzomyia series, subgenus Cellia (Diptera:Culicidae).

A total of 6 species of the Pyretophorus (4 species) and Neomyzomyia (2 species) series of the subgenus Cellia of Anopheles were used for metaphase karyotype analysis. Anopheles subpictus and An. vagus exhibit 4 and 2 forms of mitotic karyotypes, respectively, which are attributable to different types of Y chromosomes. Such distinctive mitotic chromosomes may reflect interspecies differences within each of these 2 taxa. Two distinct species, An. indefinitus and An. sundaicus, show similar metaphase karyotypes, particularly with regard to the size and shape of the sex chromosomes. Likewise, An. tessellatus and An. kochi, which are distinct species of the Neomyzomyia Series, also have metaphase karyotypes that resemble each other. They exhibit a typical feature of telocentric sex chromosomes resembling those of the An. dirus complex and the other species of the Leucosphyrus Group. Like the other cases of the Oriental Anopheles, heterochromatin has played a significant role in chromosome evolution of the 6 species.

Heterochromatin variation in chromosome X in a natural population of Anopheles willmori (Diptera: Culicidae) of Thailand.

Among the eight families of Anopheles willmori derived from individual wild-caught females collected from Chiangmai Province (northern Thailand) and examined, four isofemale lines showed variation in the X chromosome, including the normal X1 and three aberrant types (X3, X4 and XL). It is postulated that these different types of X chromosomes could have arisen as a result of spontaneous chromosomal rearrangements involving tandem translocation and paracentric inversion followed by acquisition of constitutive heterochromatin. Such rare events of chromosomal changes have become established in the natural population of An. willmori in northern Thailand.

Metaphase karyotypes of Anopheles of Thailand and Southeast Asia: V. The Myzomyia Series, subgenus Cellia (Diptera:Culicidae).

Metaphase karyotypes of 9 species of the Myzomyia Series show intra- and interspecific differences based on quantitative variation and distribution of constitutive heterochromatin in the sex chromosomes or the centromeric regions of the autosome pairs or both. Anopheles jeyporiensis and Anopheles aconitus each exhibit 4 forms of mitotic karyotypes, which may reflect interspecific differences within each taxon. The well-defined genetic species within the Anopheles minimus and the Anopheles culcifacies complexes clearly exhibit distinctive metaphase karyotypes that can be used as diagnostic characters for separating these sibling species, which are difficult to identify by morphological criteria alone. Our analysis on metaphase karyotypes of Anopheles pampanai, Anopheles varuna, and Anopheles flavirostris also confirms their morphological identification based on heterochromatin differences in the sex chromosomes and autosome 2.

Metaphase karyotypes of fruit flies of Thailand. I. Five sibling species of the Bactrocera dorsalis complex.

Natural populations of fruit flies of the Bactrocera dorsalis complex exhibit chromosomal variation based on differences in the amount and distribution of constitutive heterochromatin in the centromeric regions of the autosomes and the sex chromosomes. The chromosomal variation, coupled with differences in external morphology and host plant specific preferences, strongly suggest the existence of 5 closely related species within the B. dorsalis complex that have provisionally been designated B. dorsalis species B, C, D, and E in contrast with B. dorsalis s.s. (species A). Analysis of heterochromatin in autosomes and sex chromosomes has revealed 4 distinct groups of mitotic karyotypes. Bactrocera dorsalis is the only representative of Group I, which is characterized by the typical metacentric X chromosome and major blocks of centromeric heterochromatin in autosomes 5 and 6. Group 2 consists of species B and C, which show prominent landmarks of pericentric heterochromatin in all autosomes and in the X chromosome. Group 3 comprises species D, which is characterized by conspicuous blocks of pericentric heterochromatin in all autosomes but the long arm of the subtelocentric X chromosome is euchromatic and lacks a major portion of centromeric heterochromatin. Species E belongs to Group 4, which differs from Group 3 in having major blocks of heterochromatin at the distal portion of the X chromosome in addition to the prominent landmarks of pericentric heterochromatin in all autosomes. Chromosomal evolution among closely related species within the B. dorsalis complex clearly involves the presence or absence of constitutive heterochromatin in the centromeric regions of autosomes as well as in the X chromosome.

Metaphase karyotypes of Anopheles of Thailand and Southeast Asia: IV. The Barbirostris and Umbrosus species Groups, subgenus Anopheles (Diptera: Culicidae).

Metaphase karyotypes of 2 and 3 species of the Umbrosus and the Barbirostris Groups, respectively, of the subgenus Anopheles occurring in Thailand and Indonesia show inter- and intraspecific differences with respect to the amount and distribution of constitutive heterochromatin in the sex chromosomes and/or autosomes. Four forms of metaphase karyotypes have been recognized in the wild samples of Anopheles barbirostris based on differences in size and shape of X and Y chromosomes. It is not known whether forms A, B, and C of the metaphase karyotype of An. barbirostris found in Thailand represent inter- or intraspecific differences. However, form D, which occurs only in Indonesia, may represent a mitotic karyotype of a distinct species closely related to An. barbirostris. Anopheles campestris and An. barbumbrosus are each readily separated from An. barbirostris by mitotic chromosomes. Anopheles umbrosus and An. letifer of the Umbrosus Group also exhibit heterochromatin variation in the X chromosomes. These 2 species can be readily distinguished by the gross morphology of mitotic karyotypes, particularly the X and Y chromosomes.

Metaphase karyotypes of Anopheles of Thailand and Southeast Asia: I. The Hyrcanus Group.

Metaphase karyotypes of 6 species of the Hyrcanus Species Group of the subgenus Anopheles show constitutive heterochromatin variation in X and Y chromosomes. Anopheles peditaeniatus exhibits the most extensive variation in the size and shape of heterochromatic sex chromosomes, with 3 types of X and 5 types of Y chromosomes. Anopheles nitidus shows the least variation, with only 2 types of X chromosomes. Anopheles sinensis and An. crawfordi each have 2 forms of metaphase karyotype in the heterochromatin of the Y chromosome. It is not known whether the 2 forms of metaphase karyotype in these 2 species represent inter- or intraspecific differences. The 2 forms of heterochromatic sex chromosomes observed in An. argyropus and An. nigerrimus may suggest the existence of sibling species complexes within each of these species.

Cytogenetic evidence for a fifth species within the taxon Anopheles dirus in Thailand.

Crossbreeding and chromosomal evidence are presented for the existence of a fifth sibling species within the taxon of Anopheles dirus in Thailand. The new species is morphologically identifiable as Anopheles balabacensis "Fraser's Hill form." Structural differences in mitotic chromosomes and extensive asynapsis in hybrid polytene chromosomes indicate that significant genetic divergence exists between this species and its closest relatives, An. dirus species A, B, C and D and An. balabacensis.

Cytological differences and chromosomal rearrangements in four members of the Anopheles dirus complex (Diptera: Culicidae).

A reference photomap of the larval salivary gland, polytene chromosomes of the Anopheles dirus complex (species A) is presented. Samples of species A, B, C, and D from natural populations in Thailand were compared to this standard map using the larval progeny of wild-caught females. All species show differences in their chromosome banding patterns involving band size, number, and shape, particularly at the free ends of the X, 2R, and 2L. These differences provide useful diagnostic characters for separating members of the species complex. However, overall banding patterns are conservative in the group: species A, B, and C are virtually homosequential. Species D is highly polymorphic for a single paracentric inversion in each of the four autosomal arms and has a fixed inversion on the X chromosome. This same X chromosome inversion occurs at low frequency in species A.

Geographic distribution and biting behaviour of four species of the Anopheles dirus complex (Diptera: Culicidae) in Thailand.

A cytogenetic analysis of the species status of members of the Anopheles dirus group, from natural populations, over a six-year period has produced biogeographic and behavioural data which are presented herein. Species A, B, C and D have quite distinct geographic distributions in Thailand. Species A is the only species in most of the mainland but is absent from the southern half of the peninsula. Species B is dominant in the far south of the peninsula giving way to species C on the north-east side and rarely occurring on the west side of the peninsula; it is unknown from the northern half or the rest of the country. Species C is known from the middle eastern side of the peninsula and from a site far to the north along the Burmese border. Species D occurs down the mountains along the Burmese/Thai border and along the north half of the western peninsula. Each species appears to have distinct times of biting during the night. They also appear to have differential seasonal abundance. These data together with the differing geographic distributions suggest some implications for Plasmodium transmission and that care should be taken to identify these genetic species during malariometric studies.