Leishmaniases are among the important public health problems facing populations in the tropical and subtropical world. The wide diversity of the state of the disease and its epidemiology contributes greatly to the difficulties experienced in the control or management of the leishmaniases. Each focus of the disease calls for specific control or management strategies. Furthermore, the knowledge of the true prevalence of the disease and the extent to which it is responsible for human suffering and invalidity is lacking. However, our current knowledge of this disease indicates that it is on the increase.

The spatial distribution and abundance of galls of Phytolyma lata were investigated. There was significant correlation between gall counts and the proportion of young leaves. It is suggested that the preference for young leaves not only ensures that good quality food is available but also that the insect is able to complete development before leaf fall. The distribution was also found to be influenced by the surface of leaf, region of leaf and size of veins.

Population dynamics of pink bollworm on cotton was studied through male moths captured in the traps baited with sex pheromone ‘gossyplure’ and by its damage to the flowers and green bolls during 1978 and 1979 crop seasons. The number of pink bollworm male moths captured in traps were low up to August. Maximum moth population was recorded from the second fortnight of September to the second week of November. The population started declining after the first fortnight of November, indicating that most of the larvae had entered diapause due to the short photoperiod and low temperature. Incidence of pink bollworm on flowers was high up to the last week of August, after which it declined. While on green bolls its infestation started in the beginning of August and continued to increase up to the end of the season. A linear and highly positive correlation was found between the male moth catches in traps and the larval damage in flowers and bolls (r = 0.84 and 0.95 in 1978 and 1979 crop seasons, respectively).

Antigenic variation is a mechanism exploited by parasitic protozoa to evade the host's immune response. Studies on such variation are of cardinal importance in approaching the practical problems of vaccine design and diagnosis of infection by serological tests. Coincidently these studies have revealed novel gene expression mechanisms which are of fundamental biological interest (Vickerman and Barry, 1982). The African (salivarian) trypanosomes all exhibit antigenic variation and the process has been studied in Trypanosoma brucei subspecies in particular.

A number of resistance sources have been identified against two major pests of sorghum, viz the sorghum shootfly, Atherigona soccata Rondani, and the stem-borer, Chilo partellus (Swinhoe). These identified sources of resistance were generally tall, late maturing and poor yielders. Two of these identified sources of resistance, viz. BP 53 and M 35-I, have been utilized in the breeding programme, by crossing with dwarf exotic types, which are highly susceptible to both the pests, but are agronomically desirable varieties. The crosses thus obtained were screened for their reaction to the two pests. An extensive screening programme was carried out under heavy levels of shootfly and stem-borer infestation from 1968 to 1980, which resulted in the identification of nine advanced generation derivatives possessing moderate to high levels of resistance to both shootfly and stem-borer as well as desirable agronomic characters.

The derivatives with M 35-I, as one of the parents showed more resistance to shootfly as compared to derivatives with BP 53, as one of the parents. However, in the case of resistance to stem-borer, the reverse was true.

The first paper of this symposium was presented by Y. Tsukii (Hosei, Univ.) under the title of ‘Genes controlling the specificity of mating type and matingtype-substance interactions in Paramecium.’

Sexual reproduction in the ciliate Paramecium caudatum is initiated by ciliary agglutination (mating reaction) between cells of complementary mating types, E and O. This initial cell contact involves specific macromolecules called the ‘mating-type substances’, proteins associated with ciliary membranes. Although they have eluded all attempts at isolation, genetic approaches are disclosing their structural characteristics.