PAPER SESSION VIII: MANAGEMENT AND CONTROL OF MITES AND TICKS

CHAIRPERSON: Dr. E.O. Osir

LEAD PAPER 3

ASSESsING GENETIC VARIATION BY MOLECULAR TECHNIQUES AS A TOLL IN PEST CONTROL

M. Navajas

Institute National de la Recherche Agronomique. Centre de Biologie et de Gestion de Populations. Campus International de Baillarguet. CS 30 016. 34988 Montferrier sur Lez Cedex, France, E-mail:Navajas@ensam.inra.fr

Efficient control of agronomic pests relies on a clear understanding of the taxonomic status of the target species. Noxious organisms are often small arthropods hence the available diagnostic phenotypic characters are scarce and their taxonomy may sometimes be equivocal. Advances in molecular biology have provided data on nucleotide variation that, added to more traditional morphological features, help in establishing reliable criteria to determine pest systematics. In the Acari, the family Tetranychidae consists of about 1200 described species and includes some of the world’s major agricultural pests. These mites still constitute a problematic group for systematics and considerable experience is required to identify them. Besides providing solid taxonomic criteria, DNA based data may help in understanding the partition of the variability inside a species. In the case of pests this is a critical component of any control effort, because the amount of gene flow existing between populations, determines the diffusion risk of some agronomic important genetic traits (e.g. virulence, insecticide resistance, etc.). Moreover, an increasing number of pest species is being transported to new biogeographic regions each year and the knowledge of the patterns of geographic variation of the species can also be useful in tracing accidental pest introductions. In the past few years increasing DNA based data have became available in acari. The contribution of molecular biology techniques in acarology related to pest management is described using results obtained in my laboratory and examples from the literature. Different biological situations are approached: accurate identification of species with emphasis in distinction of sibling species, the establishment of phylogenies, appraisal of the genetic variability of the target species and tracing the biogeographic origin and diffusion of exotic pest organisms. The current molecular techniques adopted in mites are presented. Because the different DNA based markers might perform differently depending on the target species and/or the type of question addressed, a discussion on the performances of the different available markers will be included.

PAPER 29

THE ISOLATION OF GENES ENCODING SECRETORY PROTEINS FROM THE SALIVARY GLANDS OF RHIPICEPHALUS  APPENDICULATUS

B.E. Lambson¹, P. Pandit¹, O.K. ole-MoiYoi², S. Welburn³, V. Nene¹ and R.P. Bishop¹

¹International Livestock Research Institute (ILRI), PO Box 30709, Nairobi, Kenya, E-mail: b.lambson@cgiar.org

²Institute of Molecular and Cell Biology for Africa, c/o PO Box 30709, Nairobi, Kenya

³CTVM, Univ. of Edinburgh, Easter Bush Veterinary Centre, Roslin, Midlothian, UK

The tick secretes pharmacologically active salivary gland molecules into the host when feeding. These molecules are designed to increase the efficiency of feeding and may enhance the transmission of pathogens. They may also be capable of inducing resistance to further tick infestations in the host. In this study genes encoding secreted proteins are being isolated from the salivary glands of the cattle tick R. appendiculatus which is the main vector of the parasite Theileria parva which causes the lethal and economically important disease East Coast Fever in sub-Saharan Africa. These secreted proteins will be investigated further as possible anti-tick vaccine components. 

The majority of secreted and type I integral membrane precursor proteins have N-terminal signal peptides that target them to the endoplasmic reticulum. Signal sequence trap vectors can be used to isolate cDNAs that encode proteins with these N-terminal signal peptides. If the cloned cDNA encodes a signal sequence in-frame with the vector reporter gene then the reporter protein will be secreted or found on the cell surface. For this study two different signal sequence trap vectors were tested with R.appendiculatus genes chosen from the database. Only those genes with confirmed signal sequences allowed the expression of the reporter genes in both vectors. The tick cDNA library has been constructed in one of these vectors and is being screened for positive clones.

PAPER 30

THE DISPERSAL OF KAMPIMODROMUS ABERRANS BETWEEN UNCULTIVATED AREAS AND GRAPE FIELDS: DOES PESTICIDE APPLICATION AFFECT THE SETTLEMENT OF MIGRANTS?

M.-S. Tixier & S. Kreiter

Ecole Nationale Supérieure Agronomique (ENSAM) – Institut National de la Recherche Agronomique (INRA), Animal Ecology & Agricultural Zoology Unit, Laboratory of Acarology, 2 Place Pierre Viala, 34060 Montpellier cedex 01, France. E-mail: garcin@ensam.inra.fr, kreiter@ensam.inra.fr

Kampimodromus aberrans is the most important predatory mite found in vineyards in the South of France. This mite is also present in uncultivated areas and its dispersal into the vineyards was studied. High densities of K. aberrans disperse into the experimental field mainly by aerial means. In order to determine the origin of migrants, a molecular study using RAPD markers was performed. Samples of females were obtained from an experimental vineyard, and from 2 cultivated vine plots and 2 naturally occurring plants (Quercus pubescens Willd.) and Celtis australis L., both very close to the vine plot. Populations of K. aberrans seem to be highly structured and no correlation was observed between genetic and geographic distances. Despite the dispersal of high densities of mites into the plot, once in the plot, selection pressures may affect their settlement. This result confirms data on population dynamics showing that the increase of populations in the vine plot is very small in relation to the high numbers of mites reaching the plot. For determining the impact of pesticide application on settlement, insecticide resistance of K. aberrans populations collected in vine field and an oak located in close uncultivated surrounding areas were compared. The insecticide tested, quinalphos, is the most frequently applied pesticide in the plot. High resistance levels for both populations (313 for populations collected in vineyards and 52 for populations collected on oak) were found. Both populations were resistant to quinalphos. However, at the application concentration, mortality (80 and 87 %) was quite the same for the two populations. It seems that the application of this pesticide is not the major explanation of the low settlement of migrants coming from woody areas into the plot. So other studies have to be conducted to determine which other factors are involved.

PAPER 31

EXPANDING PEST STATUS OF PHYTOPHAGOUS MITES IN INDIA

J. Singh

Department of Entomology & Agricultural Zoology, Institute of Agricultural Sciences, Banaras Hindu University, Varanasi – 221005, India, E-mail: jyoti_preeti@rediffmail.com, janardan@banaras.ernet.in

Phytophagous mites are becoming a worldwide problem in agriculture. Of late, in India the injurious mites are becoming more alarming. The work conducted on expanding pest status of mite problems under the All India Coordinated Research Programme of Agricultural Acarology under the network programme of the Indian Council of Agricultural Research is reported in the present paper. The scenario of mites as pests has been established on many crops. Only the mites causing alarming infestation are highlighted in the paper. Tetranychus ludeni has been identified as a very serious mite pest on cowpea in Varanasi region of Uttar Pradesh. The early infestation of mites causes yellowing of leaves followed by necrotic patches. During heavy infestation of mites, bronzing effects on leaves are pronounced. Aggregation of mites on tips of the fruits is common during morning hours when day temperature is more than 38°C. The hot spots/ballooning symptoms have been recorded during field surveys. The reasons for outbreak of Tetranychus ludeni recorded during recent years are also discussed in the paper. The mixed population of Tetranychus neocaledonicus and Tetranychus urticae (=cinnabarinus) has also threatened the cultivation of okra and brinjal. Tetranychus macfarlanei has also been recorded on vegetables. These mites are more aggressive during summer months. During last few years, the summer brinjal was found severely infested by Aceria lycopersici. The record of this eriophyid mite is showing new trend. The winter hyacinth bean has been found severely infested by Tetranychus urticae. Cucurbetaceous plants, specially bottle gourd and pumpkin showed heavy infestation of Tetranychus urticae and Tetranychus neocaledonicus. The recent surveys also identified the presence of Tetranychus urticae on pointed gourd. The symptoms of injuries and levels of infestations are discussed in the paper. The infestation of brown mite, Petrobia latens is also covering more area on wheat, barley and coriander especially in dryland agriculture of Rajasthan. This mite needs further attention due to its expanding coverage in dryland areas of Punjab, Haryana and Western Uttar Pradesh. During recent years alarming infestation of coconut bud mite, Eriophyes gurreronis has been identified from peninsular states of India. The other mites of very serious status i.e., Aceria cajani, Aceria litchi and Aceria mangiferae are also highlighted in the paper. The paper also highlights large-scale damage caused by Polyphagotarsonemus latus on chilli. The records of predatory mites like Amblyseius alstoniae, Amblyseius longispinosus, Amblyseius multidentatus, Amblyseius tetranychivorus, Typhlodromus homalii, Cunaxa setirostris, Agistemus indusatani, Pronematus fleschneri are highlighted in the paper.

PAPER 32

A SIMPLE AND RAPID METHOD FOR A MINI PREPARATION OF HIGH MOLECULAR WEIGHT DNA FROM CERTAIN ACARINES, BACTERIA AND THE SOYBEAN PLANT

Z.A. El-Fiky

Genetics Department, Faculty of Agriculture, Fayoum Branch, Cairo University, Fayoum, Egypt

A simple, rapid and cheap method for the isolation of high molecular weight DNA from small amounts of cells or tissue within 3 - 5 hours is described. The method does not require proteinase K, costly buffers or liquid nitrogen. This method has been successfully applied to the isolation and purification of DNA from eggs of Hyalomma excavatum, H. dromedarii, Argas persicus, A. hermanni and Boophilus annulatus, in addition to Escherichia coli, actenomycetes (Nocardia sp.) and soybean leaves (Glycine max L). The DNA concentration was calculated from the OD value at wave length 260 nm and the ratios of OD₂₆₀ /OD₂₈₀ and OD₂₆₀ / OD₂₃₀ were determined. The quality and amount of DNA obtained by this method was comparable to the DNA isolated from equal amounts of materials using a commercial Genomic DNA Purification Kit.