Studies are reported on the aetiology of allergic dermatitis of horses in Australia. This disease is considered identical with a dermatitis of horses reported from India, the Philippine Islands, and the United States of America, of which the skin-infesting microfilariae of Onchocerca reticdata are claimed to be the cause. These larval helminths could not, however, be incriminated in allergic dermatitis in Australia, which proved to be due to the development of a hypersensitivity to the bites of a sandfly, Culicoides robertsi. Observations on blood histamine levels revealed that in non-susceptible horses the level was constant throughout the day and also throughout the year, whereas in susceptible animals in the summer the levels fluctuated widely during the day, reaching a maximum value at 6-9 p.m. This period coincides with the period of maximum activity of C. robertsi. Susceptible horses stabled in an insectary from 4 p.m. to 7 a.m. during the summer months did not develop the disease. The geographical and seasonal distributions of the disease are also similar to the known geographical and seasonal distributions of C. robertsi.Intradermal skin tests with antigen prepared from biting insects gave consistently positive results in susceptible animals only with C. robertsi antigen. The pathological and blood histamine pictures following the use of antigen from this insect were identical with those seen in naturally occurring cases of the disease and also following experimental biting and engorgement by this insect. Evidence was obtained of the presence in susceptible animals of a thermolabile, skin-sensitizing antibody which was capable of passive transfer. An immune antibody was demonstrated in susceptible animals, after a course of treatment with "Hapamine", by means of the precipitin test and also by the in-vitro neutralization of histamine liberated in the blood of untreated, susceptible animals. The absence of immune antibodies in non-susceptible horses is regarded as evidence that their freedom from the disease is due to an inherent immunity and not to an acquired immunity or to desensitization.

View related articlesCiting articles: 6 View citing articles Converging farmers' and scientists' perspectives on researchable constraints on organic cocoa production in Ghana: results of a diagnostic study

Cocoa (Theobroma cacao L.) is an important foreign exchange earner for Ghana. However, production is constrained by a high incidence of pests and diseases. Based on farmers' needs, this study focused on the control of capsids, mainly Sahlbergella singularis Haglund and Distantiella theobroma (Distant) (both Hemiptera: Miridae). Annual crop loss caused by capsids is estimated at 25 -30%. To control capsids, formal research recommends application of synthetic insecticides four times between August and December. However, farmers hardly adopt this recommendation, which they consider unsuitable for their conditions and context. Three alternative control methods were tested with farmers: mass trapping, using sex pheromones; applying crude aqueous neem Azadirachta indica A. Juss. (Meliaceae) seed extract (ANSE) and using the predatory ant Oecophylla longinoda Latreille (Hymenoptera: Formicidae) as a biological control agent. Contrary to most previous reports, studies on temporal distribution of cocoa capsids indicated that the population peaked in March. ANSE was effective against capsids and other cocoa insect pests and did not affect the predatory ant. When O. longinoda occurred in high numbers, capsid incidence was low. Shade did not influence ant or capsid abundance significantly. ANSE caused 100% mortality of capsids in cage and 79 -88% in field experiments. The sex pheromone was as effective as ANSE or ants in suppressing capsids. All the three methods were effective and compatible; hence, they can be used in an integrated pest management strategy for cocoa, including organic production in Ghana.

The conventional method of 'delivering' technologies recommended by researchers to farmers through extension has proved ineffective, resulting in a persistent low (3.5% over ten years) adoption of researchbased cocoa technologies. The present study was conducted in the Eastern Region of Ghana and assessed the impact of the Local Agricultural Research Committee (LARC) approach on the diffusion of capsid management knowledge and practices, developed with the LARC, to others in the community. Capsids (Sahlbergella singularis and Distantiella theobroma) were diagnosed as the most serious production constraint. LARC members engaged in intensive interactive learning and experimentation to control them. The interactive approach developed by the International Centre for Tropical Agriculture was used to link the LARC with community farmers, a majority of whom aspired to produce organic cocoa for a premium. The LARC acquired vital agro-ecological knowledge on capsid management, including skills in scouting for capsids to determine their temporal distribution and systematic experimentation with control methods, before presenting its results to the community. This article reports on a survey comparing three categories of farmers: LARC members, exposed and non-exposed community farmers, so as to assess the diffusion and impact of LARC knowledge coproduction. The results show that the LARC approach significantly influenced acquisition and diffusion of knowledge and practices.