Esther N. Mwangi

Repellent and acaricidal properties of Ocimum suave against Rhipicephalus appendiculatus ticks

An oil extracted from the leaves of a tropical shrub Ocimum suave was found to repel as well as kill all stages of the tick Rhipicephalus appendiculatus. In an in vitro bioassay for the larvae, the LC50 of the oil in liquid paraffin was 0.024%. A 10% solution was found to kill all immatures and more than 70% of adults feeding on rabbits. Rabbits were protected for 5 days against attaching larvae using a 10% solution. Preliminary experiments undertaken with cattle kept in the field suggest that the oil may have potential in tick control, and a role in integrated tick management.

The impact of Ixodiphagus hookeri, a tick parasitoid, on Ambl yomma variegatum (Acari: Ixodidae) in a field trial in Kenya

In an experiment to investigate the effect of the tick parasitoid, Ixodiphagus hookeri, on tick numbers on cattle, 150 000 parasitoids were released over a period of 1 year in a field where ten cattle infested with multiple tick species were kept. Amblyomma variegatum was reduced from 44 to two ticks per animal while Rhipicephalus appendiculatus increased over the time of parasitoid release. During the time of release 51% of the nymphs of A. variegatum collected from the animals were parasitized. The recovery of the parasitoids after the releases were stopped was only 9%. The total numbers of A. variegatum remained low up to 1 year after the parasitoid release was stopped. This study gives an insight into how I. hookeri could be used strategically for the management of A. variegatum on small-scale farms.

Predators, parasitoids and pathogens of ticks: A review

Research conducted on natural enemies of ticks, namely predators, parasitoids and pathogens, is reviewed. Predators include ants, birds, rodents, lizards, shrews, spiders and domestic chickens. All the known parasitoids are hymenopteran wasps belonging to the genera Ixodiphagus and Hunterellus. The work so far done on bacteria, fungi, viruses and rickettsiae which are pathogenic to ticks is reviewed, both with regard to experimental infections and natural infections. The possibilities of using natural enemies as biological control agents of ticks are discussed.

Predation of free-living engorged female Rhipicephalus appendiculatus.

In experiments done over a period of 1 1/2 years using engorged femaleRhipicephalus appendiculatus tethered in a grass plot, 42% predation was observed in long grass (40–60 cm), and 36% in short grass (6–10 cm). Deaths due to environmental factors were 4.8% and 6.8% in long and short grass, respectively.Six groups of animals were confirmed to be predators of the ticks, namely: ants, spiders, rodents, birds, lizards and shrews.The implications of these results in making tick population models, and the possibility of using predators in integrated tick-control packages are discussed.

Visual Evaluation and Recognition of Hosts by the Tick Parasitoid, Ixodiphagus hookeri (Hymenoptera: Encyrtidae)

The role of host size, movement, feeding status, color, and species in the visual host evaluation and recognition behavior of the tick parasitoid, Ixodiphagus hookeri Howard was investigated. Freshly emerged female parasitoids were subjected to a choice bioassay, where the test materials were placed in sealed vials and the vials placed in a Petri dish. When presented with A. variegatum live and mummified nymphs, females examined: larger nymphs significantly longer than smaller nymphs, fed nymphs significantly longer than unfed nymphs, dead and live nymphs for similar lengths of time, and grey live nymphs and yellow-brown and dark brown mummified nymphs for similar lengths of time. The total number of visits to vials containing these test materials were also not significantly different, except there were significantly more visits to yellow-brown mummies when compared to the number of visits to dark brown mummies. When presented with A. variegatum (host) and R. appendiculatus (nonhost) nymphs, the females examined A. variegatum nymphs significantly longer than R. appendiculatus nymphs. The total number of visits to vials containing A. variegatum nymphs were significantly more than the visits to the vials containing R. appendicualtus nymphs. Furthermore, females spent significantly more total examination time per visit on larger and fed A. variegatum nymphs when compared to smaller and unfed nymphs, respectively. Direct and indirect detection were significant when females were presented with fed versus unfed A. variegatum nymphs, grey nymphs versus yellow-brown mummies, and R. appendiculatus versus A. variegatum nymphs. Direct and indirect detection for the rest of the bioassays were not significantly different. Finally, The percentages of females contacting large fed A. variegatum nymphs first were significantly different from those of females contacting small unfed R. appendiculatus nymphs first. The firstcontact percentages for the rest of the bioassays were not significantly different.

Cattle and Amblyomma variegatum Odors Used in Host Habitat and Host Finding by the Tick Parasitoid, Ixodiphagus hookeri

The response of mated naive Ixodiphagus hookeri females to cattle and Amblyomma variegatum nymphal odors was tested in a Y-tube olfactometer. I. hookeri females were attracted to cattle urine, dung, and odors from tick-free feeding sites of A. variegatum nymphs on cattle, e.g., dewlaps, front heels, and hind heels. Tick-free scrotal odors did not attract the parasitoids. Furthermore, odors from off-host unfed and fed A. variegatum nymphs did not attract the parasitoids, despite an increase in the number of the nymphs to amplify any odor signal. A blend of odors from feeding on-host nymphs and cattle scrota attracted the parasitoids. In T-tube bioassays, I. hookeri females were attracted to hexane washes and fecal extracts of A. variegatum nymphs.

Drop-off patterns for engorged adult females, nymphs and larvae of Rhipicephalus appendiculatus

A drop off rhythm of engorged Rhipicephalus appendiculatus Neumann was demonstrated for females and engorged nymphs, but not for larvae. Seventy per cent of 1279 engorged R. appendiculatus females dropped off the animals between 0800 and 1000 hr, while 66% of 2736 engorged nymphs dropped between 1600 and 1800 hr.Females which were put on the animals at night (2000 hr), started to drop-off 24 hr later, than those put on in the day (0900 hr). Ticks which were fed on tick-sensitized animals also started to drop off 24 hr later, than those on tick-naive animals.The implications of these results on tick control management are discussed.RésuméRythme de détachement de femelles adultes, k]de nymphes et larves gorgées de Rhipicephalus appendiculatus. Un rythme de détachement de leurs hôtes de femelles et nymphes Rhipicephalus appendiculatus Neumann gorgées a été déjà décrit mais rien n’a été fait en ce qui concerne les larves. Soixante dix pourcent des 1279 femelles gorgées se détachent des animaux entre 0800 heures et 1000 heures tandis que 66% des 2376 nymphes gorgées tombent entre 1600 heurs et 1800 heures.Les femelles présentées aux animaux la nuit (20 heures) commencent á se détacher 24 heures après celles qui ont été mises sur les animaux le jour (9 heures). Les tiques nourries sur des animaux déjà sensibilisés commencent a se détacher 24 heures aprés celles nourries sur des animaux n’ayant jamais eu contact avec des tiques. Les implications que peuvent avoir ces résultats en matière de contrôle de tiques ont été discutées.