ABSTRACT-We investigated itch-associated responses (scratching) to mosquito bites and the role of histamine and mast cells in mosquito-induced itching in mice. Although the first bites of mosquito Aedes albopictus did not increase scratching, repeated bites increased scratching. The response was not diminished even after an interval of 2 months. Similarly, repeated intradermal (i.d.) injections of salivary gland extract (SGE) from Aedes albopictus increased scratching after SGE injection itself and mosquito bites. The scratching peaked within 10 min and almost subsided by 60 min. The opioid antagonist naloxone (1 mg / kg, s.c.) inhibited scratching following SGE injection. Although the non-sedative H 1-histamine-receptor antagonist terfenadine (30 mg/ kg, p.o.) significantly suppressed scratching induced by histamine (100 nmol /site, i.d.) in either naive or mosquito-sensitized mice, it did not affect mosquito-induced scratching in mosquitosensitized mice. Repeated injections of SGE increased scratching in mast cell-deficient (WBB6F1-W /W v ) mice as well as in normal (WBB6F1-+/ +) littermates. Repeated exposure to mosquito bites roughly doubled serum concentrations of total IgE and IgG1, but not IgG2a. Repeated injections of SGE markedly increased plasma extravasation induced by mosquito bites and such an increase was almost completely suppressed by terfenadine (30 mg/ kg, p.o.). The results show the presence of histamine-mediated and histamineindependent mechanisms in cutaneous itching and suggest that histamine probably released from mast cells does not play an important role in itching in immediate allergic reaction. Our murine model of mosquito itching may be useful for studying the mechanisms of immediate allergic itching.

The fundamental approach to the biological control of Aedes albopictus requires the mass rearing of mosquitoes and the release of highly competitive adults in the field. As the fitness of adults is highly dependent on the development of immatures, we aimed to identify the minimum feeding regime required to produce viable and competitive adults by evaluating three response parameters: development duration, immature mortality, and adult wing length. Our study suggests at least 0.60 mg/larva/day of larval diet composed of dog food, dried beef liver, yeast, and milk powder in a weight ratio of 2:1:1:1 is required to maximize adult fitness. With standardized protocols in mass rearing, intensive studies can be readily conducted on mosquito colonies to facilitate comparisons across laboratories. This study also evaluated the differences in response of laboratory and field strains under different feeding regimes. We found that strain alone did not exert substantial effects on all response parameters. However, the field strain exhibited significantly lower immature mortality than the laboratory strain under the minimum feeding regime. Females and males of the laboratory strain had longer wing lengths under nutritional constraint due to the higher mortality that resulted in reduced interactions with the remaining larvae. Meanwhile, the field strain exhibited heterogeneous duration of immature development compared with the laboratory strain. The disparities demonstrated by the two strains in this study suggest the effect of inbreeding surfaced after a long term of laboratory colonization. Despite the trade-offs resulting from laboratory colonization, the competitiveness of the laboratory strain of Ae. albopictus is comparable to the field strain, provided the larvae are fed optimally. Journal of Vector Ecology 42 (1): 105-112. 2017.

We demonstrated in this study that blood group O subjects attracted more Aedes albopictus than other blood groups (B, AB, and A) but were only significantly more attractive than blood group A subjects in 64 human landing tests. We collected saliva from the subjects and tested it for agglutination inhibition, categorized the subjects into secretors or nonsecretors, and studied mosquitoes' landing preferences for those groups. The mean relative percent landing on blood group O secretors (83.3%) was significantly higher than on group A secretors (46.5%). We also compared the attraction to subjects according to blood groups using forearm skin treated with ABH antigens. Blood group O disaccharide (H antigen) attracted significantly more Ae. albopictus than did blood group A trisaccharide (A antigen), and subjects treated with blood group A disaccharide attracted significantly more Ae. albopictus than did subjects treated with blood group B trisaccharide (B antigen), but ABH antigens did not, in general, influence the landing preference of mosquitoes among ABO blood groups.

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Proboscis amputation has facilitated the study of mosquito behavior. Using humans as a host is very important in the study of mosquito attractants, repellents, and host preference. However, mosquito bites cause potential medical problems because of hypersensitivity and perhaps secondary bacterial infection, even using laboratory mosquitoes. Moreover, once a normal female mosquito bites and feeds on human blood, it cannot be used in subsequent probing tests. These problems were resolved by proboscis amputation. Variation of attraction among humans was examined effectively without bites using proboscis-amputated Aedes albopictus Skuse. Proboscis-amputated and normal mosquitoes also showed equal repellency against 1% L-lactic acid. Although the mosquitoes lacked the tip of the labium and some sensilla, they alighted on human forearms in the same way as normal mosquitoes. Because proboscis-amputated mosquitoes continued to probe avidly, they could be used repeatedly, thereby reducing the number of mosquitoes required for experimentation. The use of proboscis-amputated mosquitoes would promote various studies of mosquito attraction or repellency with no risk of hypersensitivity and secondary bacterial infection by mosquito bites.