Evaluation of pseudostem trapping as a control measure against banana weevil, Cosmopolites sordidus (Coleoptera: Curculionidae) in Uganda.

Controlled studies to determine the efficacy of pseudostem trapping in reducing adult populations of the banana weevil, Cosmopolites sordidus (Germar), were conducted under farmer conditions in Ntungamo district, Uganda. Twenty-seven farms were stratified on the basis of C. sordidus population density (estimated by mark and recapture methods) and divided among three treatments: (i) researcher-managed trapping (one trap per mat per month): (ii) farmer-managed trapping (trap intensity at discretion of farmer); and (iii) controls (no trapping). Intensive trapping (managed by researchers) resulted in significantly lower C. sordidus damage after one year. Over the same period, C. sordidus numbers declined by 61% on farms where trapping was managed by researchers, 53% where farmers managed trapping and 38% on farms without trapping; however, results varied greatly among farms and, overall, there was no significant effect of trapping on C. sordidus numbers. Moreover, there was only a weak relationship between the number of C. sordidus removed and the change in population density. Trapping success appeared to be affected by management levels and immigration from neighbouring farms. Although farmers were convinced that trapping was beneficial, adoption has been low due to resource requirements.

Towards the selection of cattle for tick resistance in Africa.

Half-body tick collections and visual assessment of tick burdens were performed monthly over six months on 100 bulls at the Kenya National Boran Stud, Mutara Ranch, Kenya. Boophilus decoloratus predominated among several tick species infesting the animals. Burdens of B. decoloratus and total tick burdens were highly correlated. Rankings of relative tick resistance among bulls were consistent from month to month. Rankings based on visual assessment were very close to those based on actual tick burdens. Animals with thin skins appeared to carry fewer ticks, but tick burden bore no relationship to coat colour. The results suggest that simple visual inspection of total tick burdens may be a suitable basis for the selection of tick resistance in cattle.

Tick (Acari: Ixodidae) infestations on Zebu cattle in western Kenya: seasonal dynamics of four species of ticks on traditionally managed cattle.

A study was conducted on the population dynamics of four tick species infesting livestock on Rusinga Island. Infestations of Rhipicephalus appendiculatus Neumann, Rhipicephalus evertsi evertsi Neumann, Amblyomma variegatum (F.)., and Boophilus decoloratus (Koch) were monitored on East African shorthorn Zebu cattle at monthly intervals for 2 yr. These cattle were of unimproved stock under traditional husbandry without any tick control practices. Most ticks were on cattle between September and March, with a peak in December-February. Following the onset of the rainy season in April, tick numbers on the cattle declined markedly; this decline continued until July or August, when numbers started to increase again. No significant correlation could be made between these population changes and any of the four climatic factors recorded. Instead, there was a notable relationship between tick population changes and local farming practice. The area and duration of cattle grazing activity were severely curtailed during the cropping season from April to September, which reduced tick-host contact and thus the tick burdens of the cattle at that time.

Histopathology of attachment sites of Amblyomma variegatum and Rhipicephalus appendiculatus on zebu cattle of varying resistance to ticks.

Mature, unimproved East African Zebu cattle (Bos indicus) naturally exposed to ticks from birth were ranked for resistance to ticks by repeated whole-body counts of infesting ticks. Four cattle of high resistance, four of low resistance and two of intermediate resistance were artificially infested with nymphs of Amblyomma variegatum and Rhipicephalus appendiculatus. Two Friesian cattle (Bos taurus) with less exposure to ticks were similarly infested. Biopsies of tick attachment sites were examined histologically. All attachment sites showed acute inflammatory lesions, and sites of both tick species on high resistance cattle showed delayed hypersensitive reactions with intra-epidermal pustulation and significant increases in the numbers of granulocytes. The predominant cells infiltrating attachment sites on high resistance cattle were eosinophils with A. variegatum and neutrophils with R. appendiculatus. Such differences need to be taken into account in developing immunological tests for selecting cattle for resistance but there are sufficient common features of reactions to the two infesting tick species to justify dermal hypersensitivity tests.

Tick infestations on Zebu cattle in western Kenya: individual host variation.

Monthly collections were made of all ticks from 25 mature East African Zebu cattle and 5 yearlings for 13 mo on Rusinga Island, Lake Victoria, Kenya, from September 1986 to September 1987. The most common species were Rhipicephalus appendiculatus Neumann and Amblyomma variegatum F.; Boophilus decoloratus Koch and Rhipicephalus evertsi evertsi Neumann also were present in fewer numbers. Cattle were ranked according to their degree of resistance to each of the four species and to each stage in the life cycle of the three-host ticks. Ranking according to infestations of females and nymphs of R. appendiculatus, nymphs and larvae of A. variegatum, or all three stages of these two species when compared with the total burden gave statistically significant correlations. Sampling difficulties prevented the ranking of cattle for infestations of larvae of R. appendiculatus, although the numbers on cattle were high. On the other hand, failure of attempts to rank the cattle on females of A. variegatum, B. decoloratus, or R. e. evertsi counts was attributed to the small differences between tick numbers on cattle. Highly resistant cattle showed little or no seasonal fluctuations in tick numbers for most of the period compared with animals of low resistance, which showed an up to sevenfold increase in the magnitude of the tick burden when the tick challenge was high. Cattle with low resistance were responsible for much of the tick multiplication in the field, whereas highly resistant animals tended to limit the populations. There were no distinct differences between the numbers of each tick species on yearlings and mature cattle.

Tick infestations on Zebu cattle in western Kenya: quantitative assessment of host resistance.

Groups of previously tick-exposed East African Zebu cattle together with tick-susceptible Friesian steers as controls were artificially infested with adults, nymphs, and larvae of Rhipicephalus appendiculatus Neumann on two occasions. Comparison of the feeding performance data from the two different breeds of cattle showed significant differences in the number and weight of engorged females and the weight of engorged nymphs. Data from the first challenge were used to derive a function for discriminating between resistant and susceptible categories. The use of the function gave repeatable results on resistance rankings when compared with original ranking of cattle based on natural tick counts following natural exposure. The function was converted into an index that could then be used to monitor the seasonal and annual fluctuations in tick resistance rankings of individual animals in a herd.

Feeding responses ofChilo partellus (Swinhoe) (Lepidoptera: Pyralidae) larvae to sorghum plant phenolics and their analogs.

Phagostimulatory responses of third-instar larvae ofChilo Partellus to phenolic components identified in an ethyl acetate extract of the leaf whorls of 3-week-old plants ofSorghum bicolor cultivar IS 18363 were studied in no-choice bioassays. The major components in the extract were identified as 4-hydroxybenzaldehyde and 4-hydroxybenzoic acid, with 4-hydroxy-3-methoxycinnamic acid, 3,4-dihydroxycinnamic acid, and 4-hydroxycinnamic acid present in minor amounts. All but 4-hydroxycinnamic acid were stimulatory at the doses tested. 4-Hydroxybenzaldehyde was more stimulatory than other potential biogenetic analogs. Hydroxybenzoic acids generally elicited greater feeding response than cinnamic acids, and the pattern of oxygen substitution in the benzene ring was related to bioactivity.

Histological reactions to bites of Amblyomma variagatum and Rhipicephalus appendiculatus (Acari: Ixodidae) fed simultaneously on naive or sensitized rabbits.

Histopathological studies on attachment sites of nymphs, 48 h after attachment on three groups of rabbits, have revealed differences that were related to the rabbits' previous tick experience. Feeding lesions caused by Amblyomma variegatum (F.) in tick-naive rabbits were extensive and the total number of inflammatory cells was about 10 times greater than that in the feeding lesions caused by Rhipicephalus appendiculatus Neumann fed simultaneously on contralateral ears. Rabbits that were previously sensitized either to A. variegatum or R. appendiculatus by repeated tick infestations showed epidermal vesiculation and significant mobilization of eosinophils at the homologous tick feeding sites, events that did not occur with tick-naive rabbits. The feeding of A. variegatum nymphs on rabbits sensitized to R. appendiculatus produced a similar type of intense reaction, but the cellular responses to R. appendiculatus in the skin of rabbits sensitized to the A. variegatum were negligible.