Cassava brown streak virus disease (CBSD) has been a serious and most damaging disease in cassava crop throughout the East, Central and Southern part of Africa. Several cassava varieties invariably respond to the disease, but the effect of the disease on affected varieties was not known. The current study was conducted to assess the ability of some farmer-preferred CBSD-affected varieties to withstand the disease. Field experiments were conducted at Kibaha Agricultural Research station from 2006 to 2008. The inherent variety characteristics influenced the incidence and severity levels of CBSD in the test plants. Leaf and stem CBSD incidences and severities, root weight and number of whiteflies (vectors) were significantly (P<0.001) related to the individual variety. Varieties Albert, Cheupe, Kibaha and Nachinyaya were seriously affected. The CBSD incidences and severities in these varieties increased with plant age, with highest disease records starting at nine to twelve months after planting. Dual infections of CBSD and CMD were recorded in four (Cheupe, Kibaha, Namikonga and Nachinyaya) of the five test varieties. Namikonga was proven to be resistant to CBSD. The correlation analysis suggested a significantly positive relationship between the perceived disease vector, Bemisia tabaci and the incidence and severities of CBSD and CMD. It was concluded that different varieties responds differently to CBSD and the disease severity increases with plant age.

No abstract

Species diversity, abundance, and dispersion of rice stem borers in framer’s fields were studied in four major rice growing areas of Kahama District. Stem borer larvae were extracted from the damaged tillers in 16 quadrants established in each field. Adult Moths were trapped by light traps and collected in vials for identification. Results indicated the presence of Chilo partellus, Maliarpha separatella, and Sesamia calamistis in all study areas. The most abundant species was C. partellus (48.6%) followed by M. separatella (35.4%) and S. calamistis was least abundant (16.1%). Stem borers dispersion was aggregated along the edges of rice fields in three locations (wards) namely: Bulige, Chela, and Ngaya. The dispersion in the fourth ward, Kashishi was uniform as established from two of the three dispersion indices tested. Further studies would be required to establish the available alternative hosts, the extent of economic losses and the distribution of rice stem borers in the rest of the Lake zone of Tanzania.

Diagnosis of Cassava brown streak disease (CBSD) has for long been based on foliar and root symptoms expression on infected plants. Variability in patterns of symptoms expression between varieties and seasons however, has meant that symptom-based diagnostics are unreliable. The current study established the relationship between symptom expression on cassava plants and the infection with Cassava brown streak virus (CBSV) using RT-PCR diagnostic tool. It was established that manifestation of CBSD-like symptoms (particularly the foliar chloroses and necrotic blotches) may not be an absolute indication of CBSV-infection. Only 67% of tested samples were both foliarly symptomatic and infected by the virus. About 22% of samples were free from CBSV despite being foliarly symptomatic and 7% were CBSV-infected but foliarly symptom less. Some CBSV-infected plants did not exhibit any foliar symptoms although had root necroses. A few CBSV-free plants were regenerated from infected cuttings in one of the four tested cultivars, Albert. Five out of fifteen (33%) plants cv. Albert were symptom less and two out of the five (40%) were CBSV-free. The findings from this study suggest that symptoms-based diagnosing for CBSV infections is unreliable. As some of CBSV-infected plants tend to be considered CBSV-free due to lack of the disease symptoms, the scenario might have contributed to unlimited spread of CBSD through latently-infected planting materials.

Mating in most species of ants occurs during nuptial flights. In the African weaver ant, Oecophylla longinoda Latreille, mating has previously been hypothesized to take place within the nest before the nuptial flight. However, several researchers disagree with this supposition particularly with reference to the closely related species Oecopylla smaragdina (Fabricius) whose mating occur during nuptial flights. Understanding the mating strategy of O. longinoda is of importance for its successful application in biological control programs. We conducted field and screen house experiments during two mating seasons to determine whether the mating occur prior to the dispersal flight. We examined winged O. longinoda queens on the nest surface before taking flight, immediately after leaving the nest, up to twelve hours (12h) after leaving the nest and after settling naturally following the dispersal flights. Mating in captivity between different number of males and queens were also assessed. Only eggs produced by queens (N=65) collected after their natural settling hatched into larvae. No eggs hatched from any of the 527 winged queens that were collected prior to their dispersal flights and no mating attempts in captivity lead to viable offspring. Findings from the current study suggest that mating of O. longinoda queens take place during a nuptial flight and does not take place within the nest, as previously suggested.