PAPER SESSION II: BIOLOGY AND DIVERSITY OF THE ACARI
CHAIRPERSON: Dr. R.O. Maranga
PAPER 6
ON A COLLECTION OF PLANT MITES
(ACARINA: MESOSTIGMATA) FROM THE
A.K. Bhattacharyya
Desert Regional Station, Zoological Survey of India, Jhalamand, Pali Road, Jodhpur 342 005, Rajasthan, India. E-mail: asitzsi@usa.net
The Thar Desert of Rajasthan, situated in the northwestern part of India is considered as the second largest desert of the world. Considering the huge plant diversity of this region virtually very little work has been done on plant associated acarine fauna. According to latest information, 65 species are known from this region. To improve the knowledge on plant mites the author conducted a preliminary study and collected nearly 240 specimens from 21 localities. Nine species of plants were examined. Mainly the agricultural crops were checked for the collection of mites. The specimens were found to belong to three species viz., Amblyseius alstoniae, A. delhiensis and Abrolophus delhiensis. The crops were often heavily sprayed with synthetic pyrethroids. Amblyseius delhiensis showed its abundance to about 95%. The first two species are well known for their use as biocontrol agents for different phytophagous mites and insects such as cotton jassids. It has been observed that the population of A. delhiensis is inversely proportional with the increase of temperature and attains peak during October to November. On the other hand, A. alstoniae population showed its dominance throughout the year. Economic importance of Abrolophus delhiensis is not well studied. Except A. alstoniae the other two species are recorded for the first time from the Thar Desert.
PAPER 7
RICCARDOELLA OUDEMANSI (THOR) AND R. LIMACUM (SCHRANK) (ACARI: ERYNETIDAE) RECORDED FOR THE FIRST TIME FROM SOUTH AFRICA.
E.A. Ueckermann1 & L.R. Tiedt2
1ARC-Plant Protection Research Institute, Private Bag X134, Pretoria, 0001, South Africa. E-mail: rieteau@plant2.agric.za
2Potchefstroom University for C.H.E., Laboratory for Electron Microscopy, Private Bag X6001, Potchefstroom, 2520, South Africa. E-mail: emslrt@puknet.puk.ac.za
To date five species of the genus Riccardoella are described, namely, R. limacum (Schrank), R. oudemansi (Thor), R. reaumuri Fain & Van Goethem, R. canadensis Fain & Van Goethem and R. triodopsis Fain & Klompen, from slugs (Family Limacidae) and snails (Fam. Helicidae). Of these species R. limacum, and R. oudemansi are the best known and are becoming pests in snail cultures, but can also be bio-control agents in other situations. These mites live on the surface or in the mantle cavity of their hosts. The presence of large numbers of R. limacum causes blood (haemolymph) loss and may even kill their mollusc hosts. It obtains the blood by producing a feeding tube in the tissues of the host with its salvia. The female deposits her eggs in the mucus of the mantle cavity. Mobile mites detect their host by following the slime trails. The life cycle of these mites consists of an egg, six-legged larva, eight-legged proto- (difficult to find), deuto-, and tritonymph and the adults. This study deals with an electron microscopy study of R. limacum found on the snail Helix aspersa Müller (Helicidae) in gardens in Pretoria. Riccardoella oudemansi was collected from only one locality from the same host. The former appears to be the dominant species. Surveys to establish the distribution of these mites and probably new species will be continued.
PAPER 8:
SURVIVAL OF ENGORGED AMBLYOMMA
VARIEGATUM NYMPHS ON A TYPICAL WEST AFRICAN SAVANNAH IN
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
The density of Amblyomma variegatum adults on a pasture depends firstly on the distribution of the engorged nymphs, and secondly on the survival rate of the ticks. This survival was studied for different cohorts of ticks placed from November to February (beginning of the dry season) on a woody and shrubby savannah. Ticks were placed in plastic bottles or in 50x50 cm cages slightly driven in the soil. The different setups were afterwards checked fortnightly. It was observed that the moulting period of the nymphs lasted 4 to 7 weeks, depending on the temperature. This means that unfed adults are present on the pastures four to five months before they are becoming active (the tick activation follows the first rains, beginning earlier for the males than for the females). The survival rate of the unfed adults did not vary according to their age, i.e. to the detachment period of the engorged nymphs. On the other hand, high variations were observed during the hot dry season (from March to May) for ticks of the same age depending on the place where they had been placed: within a few metres, the survival rate could vary from 0 to 90%, presumably because of the presence or absence of predators (mainly ants). On average, the survival rate of the ticks, at the beginning of the rainy season, was 20 to 25%. As only one environment (woody savannah) was examined, it is not possible to assess whether this survival rate varies according to the soil type or to the vegetation, or whether the impact of the predators also varies depending on these factors. Nevertheless, these results show that the predators have a great impact on the natural population of A. variegatum adults, but also that this impact is highly variable and probably unpredictable.
PAPER 9:
THE ULTRASTRUCTURE OF HALLER’S ORGAN AS EXPRESSED IN AMBLYOMMA HEBRAEUM, AMBLYOMMA GEMMA AND AMBLYOMMA MARMOREUM
1 Dept of Biology, 2Dept of Anatomy, 3Electron Microscope Unit, Medical University of Southern Africa, P.O. Box 139, Medunsa, 0204, South Africa,. E-mail: clark@medunsa.ca.za
Theiler, 1962 recognises 21 Amblyomma species in the Afro-tropical region. Ten of these are capable of transmitting Cowdria ruminantium. The survival of a specific tick species depends on how successfully it can locate a host and a mate. Host and mate location is facilitated through a specialised organ, Haller’s organ, that is situated on the dorsal surface of the tarsi of appendage I. This unique organ consists of a number of sensory setae and sensilla, which are strongly innervated. Besides olfaction, some of these sensilla have been found to function in a hygrosensory, mechanosensory, thermosensory and gustatory role. Three species of Amblyomma that act as vectors of C. ruminantium were selected. Both A. hebraeum and A. gemma parasitise livestock and large ungulates (mammals) as adults, but are geographically completely isolated from each other. The distribution of the third species, A. marmoreum corresponds roughly with that of A. hebraeum but this species parasitises tortoises and large varanids (reptiles) as adults. Males and females of each species were preserved in 70% ethanol, after submersing them in hot water (70oC). The first appendages were removed and prepared for viewing in a Leica Stereoscan 420 scanning electron microscope (SEM) at 5 to 10 kV. The composition and ultrastructure of Haller’s organ as it is expressed in the three species were compared. The sensory structures were grouped into the pre-capsular setae, anterior pit setae surrounded by a cuticular fold, a number of sensillae contained within a capsule with a thin slit-like aperture, and a post capsular group. In spite of the differences in host prevalence and habitat, no major differences in the number and grouping of the sensilla could be found. Obvious differences in the microstructure could, however, be demonstrated.