PAPER SESSION VI: MANAGEMENT AND CONTROL OF MITES AND TICKS

CHAIRPERSON: Prof. F.C. Clarke

PAPER 23

Release and establishment of Exotic Predatory Mites (Acari: Phytoseiidae) for biological control of the Cassava Green Mite Mononychellus tanajoa (Acari: Tetranychidae) in Zambia

M. Mebelo¹, R. Hanna² & C. Malambo³

¹Mansa Technology Assessment Site, Box 710129, Mansa, Zambia, E-mail: nlccp@zamtel.zm

²Biological Control Centre for Africa, International Institute of Tropical Agriculture (IITA), 08 BP 0932 Cotonou, Benin

³Misamfu Regional Research Station, Box 410055, Kasama, Zambia

Efforts at the biological control of the cassava green mite Mononychellus tanajoa have been going on since 1984 after the pest was first observed damaging cassava. Between 1984 and 1994 several strains belonging to six species Neoseiulus idaeus, Neoseiulus anonymous, Euseius concordis, Galendromus annectens, Typhlodromalus manihoti, and Typhlodromalus limonicus imported from Brazil and Colombia, were released in several locations in Zambia. Of the six species, only N. idaeus was recovered after being released in several locations for periods ranging from one to three months before it also disappeared. In 1994 another predatory mite Typhlodromalus aripo was released initially in the Northwestern province and later in Luapula province. The newly introduced species gave some promising results with recoveries made over a period of one month to six months in Luapula and Northwestern provinces before it also disappeared. From 1999 there has been a change in the release strategy to take into account climatic and ecological factors. Emphasis has been placed on identifying varieties with good characteristics such as tip size, compactness, and hairiness. In addition sites near or along shores of lakes and other wetlands are given priority as they may act as reservoir sites during unfavourable weather. The new strategy seems to be paying off as T. aripo is now established in many locations in Luapula province and has persisted in most release sites since November 1999. Several varieties preferred by T. aripo have been identified. Studies on the population dynamics of the pest and its predator have been initiated. It has also been observed that an increase in T. aripo density leads to a corresponding decline in M. tanajoa density an indicator of the predator’s capacity to control the pest.

PAPER 24

COULD LIVESTOCK KEEPERS AVOID TO GRAZE THEIR CATTLE ON PASTURES HIGHLY INFESTED BY AMBLYOMMA VARIEGATUM TICKS?

F. Stachurski, S. Zoungrana, M. Konkobo

Centre International de Recherche-Développement en zone Sub-humide (CIRDES), BP454, Bobo-Dioulasso, Burkina Faso, E-mail: Stachurski@fasonet.bf

Amblyomma variegatum is the most harmful tick species for the domestic ruminants in West Africa. Whereas tick control in the traditional herds was until recently generally done by manual removal, livestock keepers, even those involved in low-input systems, are now increasingly using acaricides. But, these products are expensive and are often misused. Therefore, complementary control methods are required, aiming at limiting cattle infestation, which may consequently allow a reduced use of acaricides. To identify such methods, studies were carried out in order to know better the relationships between the tick and its cattle host. Emphasis was put on the identification of the pastures where the contact between hosts and ticks occurs. As the distribution of adult ticks is mainly dependent on that of engorged nymphs, the distribution of this particular stage was first studied. This was carried out in an area adjacent to Bobo-Dioulasso where cattle are the main hosts of the nymphs. The daily drop-off rhythm of the ticks was determined, and the movements of some herds during the nymph infestation period were recorded. Adult distribution could however not be inferred from that of the engorged nymphs since data on the survival rate according to the pasture types were not available. Adult distribution was therefore directly assessed by examination of the infestation of "tracer cattle" kept during three successive days in enclosures of 2,500 m², or followed during fifteen days when they grazed on natural pastures. It appeared that tick distribution was very heterogeneous, adult density varying from one hundred to several thousands per hectare. However, as the most infested areas are the lowlands, where the animals are taken to graze during the beginning of the rainy and the dry seasons, avoidance of ticks seems to be impossible.

PAPER 25

CONSEQUENCES OF EXPERIMENTAL REMOVAL OF UNGULATES FOR TICK ABUNDANCE IN CENTRAL KENYA

F. Keesing¹, R.S. Ostfeld², B. Allan³ & G. Means¹

¹Bard College, Annandale, NY, USA 12504, E-mail: keesing@bard.edu

²Inst. of Ecosystem Studies, Millbrook, NY, USA 12545

³Mpala Research Centre, P.O. Box 555, Nanyuki, Kenya, E-mail: ballan@mpala.org

Ticks are important vectors of human and livestock diseases throughout Africa. In black cotton habitat in central Kenya, two species of ticks, Rhipicephalus praetextatus and R. pulchellus, are common. We investigated the abundance of these species over two years on experimental plots from which different combinations of large mammals have been excluded since 1995. Plots (200m by 200m) consist of three replicates of each of 6 treatments. The six treatments exclude different combinations of cattle, megaherbivores (giraffes and elephants), and other native ungulates. Since September 1999, we have conducted monthly sampling of ticks on all treatments. In general, plots that allow access by native ungulates had significantly higher densities of ticks than did plots that allowed only cattle, or those that excluded all ungulates. Virtually no larval ticks were found on plots without native large mammals. R. pulchellus adults were at highest densities on plots allowing only native wildlife, while R. praetextatus adults were most abundant on plots from which all large mammals had been excluded, suggesting very different host preferences for these two species. We found pronounced intra- and interannual variation in abundance of ticks, especially larvae. Because previous research has demonstrated that small mammals, particularly the pouched mouse (Saccostomus mearnsi), reach high densities in the absence of large mammals at this site, we tested whether pouched mice were adequate hosts for larval ticks. Mice had no natural tick burdens at the time of the test, and were found to be very effective at grooming off larvae placed on them in the lab. Together, these results suggest that the most abundant small mammal at this site may be a poor host for larval ticks, and that the presence of ungulates is necessary for the completion of the R. pulchellus life cycle but not that of R. praetextatus.