Download Diagnostic Methods for Spider Mites Family

Diagnostic Methods
for
Spider Mites
Family: Tetranychidae
This Diagnostic Protocol can be constantly updated and is only correct at time of printing
(Saturday 13th of May 2017 at 06:20:54 AM).
The website http://www.padil.gov.au/pbt should be consulted to ensure you have the most
current version before relying on the information contained.
Introduction
Tetranychid or spider mites are important pests of cotton worldwide. They feed on the
undersides of leaves causing a reduction in photosynthetic capacity of plants, thereby reducing
yield and in severe cases fibre quality, seed oil content and seed viability. Spider mite
populations are usually well controlled by a range of natural enemies. However, control of
primary pests, especially Lepidoptera such as the Heliothis / Helicoverpa complex, often
decimates natural enemies leading to outbreaks of spider mites. Hence they are commonly
referred to as secondary or induced pests. Control is often expensive and spider mites develop
resistance to acaricides quickly. Three species of tetranychids are recorded from cotton in
Australia; Tetranychus urticae Koch which is the major problem, T. ludeni Zacher, a minor
problem and T. lambi Pritchard and Baker which is rarely a pest. The main threat identified is
due to new species entering that are more damaging to the crop, use a different alternative host
range allowing them to become a more serious problem than current species or that are carrying
new acaricide resistance genes making them more difficult to control. This could lead to a
greater need for control and incur greater risks of populations developing acaricide resistance.
This could have flow on effects survival of beneficial
populations, resurgence of other pests and environmental contamination.
Mites in the family Tetranychidae are called 'spider' mites because they often spin protective silk
webs. This family has about 1,200 described species world wide. In Australia, there are 54
described species of tetranychid mites (Bolland, et al., 1998).
Most spider mites are polyphagous and they are distributed mainly in the North and South
Temperate Zones as well as tropical areas. Spider mites are soft-bodied with long, needle-like
movable digit of chelicera. An average adult female is 400μm in size, often red, green, orange or
yellow in color when alive.
Biology
Stages of Development
The life cycle of a spider mite consists of five developmental stages: egg, larva, protonymph,
deutonymph and adult. Development from egg to adult often takes one to two weeks or more,
depending on the mite species, temperature, host plants, humidity and other environmental
factors (Zhang, 2003). The lower threshold for development is about 12°C (53.6°F), whereas the
maximum upper limit to the development is about 40°C (104°F) (Jeppson et al. 1975).
Figure 1. The lifecycle of the two-spotted spider mite. (Jeppson et al. 1975)
The two spotted mite, Tetranychus urticae Koch, takes 8-12 days at 30-32°C to complete its life
cycle (Figure 1).
Female two-spotted mites can lay more than 100 eggs during their life duration of approximately
30 days (Jeppson, et al. 1975).
The change in spider mite populations has been affected by many factors. Climate and hosts are
the most important factors. In China, research showed that temperature was a main factor
affecting the mites' development. For example, the average adult life span of A. viennensis was
19.5-24.2 days at 17.8-23.50C but only 5.3-7.4 days at 27.80C (Wang, 1981). Most spider mites
prefer warm and dry conditions. Suitable conditions could speed up the mites' life cycles.
Spider mites oviposit singly and directly on the host leaf surfaces. Some species of spider mites
prefer to colonize and lay eggs on the underside of the plant leaf, however, some species are
often found on the upper surface of the leaf.
There are many natural enemies of spider mites. Jeppson et al. (1975) lists 28 species of
phytoseiid mites which are important predators of tetranychid mites on various crops. Young and
Zhang (1998) recorded predatory thrips, Scolothrips ?sexmaculatus (Pergande), green lacewing,
Mallada basalis (Walker) and cecidomyiid fly maggot, Feltiella acarivora Zehntner feeding on
two spotted-mites in the Northern Territory.
All the tetranychids mites share a basically similar shape, though there are variations in size and
colouration. More information on the species attacking cotton can be found in Gutierrez (1994)
or Leigh (1985).
Adult:
Females have an ovoid shape when viewed from above, about 0.3-0.5 mm in length. Eight legs,
wingless. There are usually two red eyespots near the front of the body (propodosoma).
Colouration of the nondiapause form (see below) is usually a pale green with one or more pairs
of dark green spots along either side of the body, or in some species the body is a deep red
(carmine) with dark almost black spots on either side of the body. Identification of species from
adult females is not regarded as reliable. In winter in more temperat regions female mites may
change to the diapause form. This is usually similar in size to the summer form but is usually a
bright orange colour.
Males are smaller than females and from above have a tapered shape. Eight legs, no wings.
Colour is generally pale yellow or orange with no spots.
Eggs are typically laid in shelterd location such as along leaf vains or in leaf folds. They are
round, almost clear and about 0.1 mm in diameter. Thay may become pale brown just before
hatching.
Nymphal stages. Eggs hatch into first instar 'larvae' which are white, oval shaped, about 0.1 mm
long and have six legs. These moult into the protonymph, detonymph then adult. Each stage is
successively larger, and these all tend to be pale green or pink/orange with dark spots on the
sides. Between each moult is a short quiescent period, known as the protochrysalis,
deutochrysalis and teliochrysalis respectively.
Host Range
Most of the spider mites have moderate to very broad host ranges, including a range of
agricultural and horticultural crops (cotton, soybeans, corn, sorghum, sunflower, safflower, field
peas, faba beans, strawberries, pears, apples, palms) and nursery and garden plants and broad
leafed weeds (see Leigh 1985 and Gutierrez 1994) for more details.
Distribution
Tetranychus lombardini; Africa, Australia, Madagascar, Indonesia
T. turkestani; North America, South Africa
T. pacificus; Western USA, Mexico
T. desertorum; Southern USA, central and south America, China, Japan
T. piercei; SE Asia, Philippines
T. gloveri; Southern USA, central and south America, Guam
T. cinnabarinus; tropical areas world-wide
Potential distribution in Australia
Many of these spider mite species could become pests over all or part of the cotton industry,
depending
on particular environmental preferences.
Spider Mites are distributed mainly in the North and South Temperate Zones as well as tropical
areas.
A total of 54 species of spider mites have been recorded in Australia (Bolland et al. 1998), some
are exotic but have established in Australia. There are many economically significant species,
which have been recorded in South-east Asia and China but so far have not been found in
Australia, such as A. viennensis, T. piercei McGregor, T. truncatus Ehara, T. turkestani (Ugarov
& Nikolskii) and T. yusti McGregor. However, these species have a very high potential to
establish in Australia, especially Northern Australia due to the similarities in climatic conditions
and the existence of a wide range of host plants.
Transmission
Adult females are the main migrants. Crawling is a common means of migration, especially for
movement on a single plant but also for movement to other plants should they be in contact (e.g.
in agricultural monocultures). Aerial movement on wind currents is also important, especially
within large host patches and between host patches. Although aerial dispersal is passive, mites
have a complex behaviour pattern that facilitates their becoming air borne. This behaviour is
evident when local host quality declines and mites become positively phototactic. As a result
mites move upwards towards the pheriphery of their host plants where they form aggregations.
Here they adopt a posture to facilitate dispersal by wind currents by facing away from the source
of light with their forelegs raised upright above their bodies. This only occurs in the presence of
both wind and light.
Effect
Spider mites are one of the most economically significant plant pests. Some of these mites cause
serious damage to many agricultural crops over the world. A record from China showed that the
hawthorn spider mite, Amphitetranychus viennensis (Zacher) could cause 30-67% of reduction in
apple yield and Schizotetranychus yoshimekii Ehara & Wongsiri could lead to a reduction in rice
yield of up to 30% (Wang, 1981).
Some spider mites can act as vectors in transmiting plant diseases. Jeppson et al. (1975) states
that the Potato virus Y., which affects potato, tomato, tobacco and other Solanaceae, can be
transmitted by the two-spotted mite. The two-spotted mite can also transmit tobacco ring spot
virus, tobacco mosaic virus, southern bean mosaic virus and cotton curliness.
Risk Analysis
The following risk analysis for A. gossypii (exotic strains) is based on the methodology in
Biosecurity Australia's guidelines on Import Risk Analysis for Plants and Plant Products (2001).
Entry potential
Rating = MEDIUM / HIGH
Spider mites are small and easily overlooked, and many have broad host ranges. They are
common pests in horticultural and garden nurseries, and may be accidentally imported on plant
material. Diapause forms which do not feed could survive considerable periods without food and
in cold conditions.
Establishment potential
Rating = MEDIUM / HIGH
Established in Australia already. New strains would be expected to establish readily.
Spread potential following establishment
Rating = MEDIUM
Could be spread by the nursery and horticultural industries. Spider mites cannot fly which limits
capacity for rapid spread.
Economic impact
Rating = MEDIUM / HIGH
Spider mites can cause significant reductions of cotton yield and fibre quality and can be difficult
and costly to control. Additionally they often develop resistance to acaricides used for control.
However, most spider mite species are effectively controlled by beneficial insects and mites
unless these are disrupted by insecticides. Good IPM practice in cotton could therefore moderate
the damage potential of these pests. Additionally, seasonal rainfall patterns have a big influence
on the abundance of winter weeds that act as alternative hosts for mites - dry winters can
substantially reduce overwinter success and the risk of spider mite outbreaks in the following
cotton season.
Environmental impact
Rating = MEDIUM / HIGH
Spider mites could affacte a range of other crops but also a wide range of weed species..
Conclusions
Overall risk: Rating = MEDIUM / HIGH
Potential to cause damage is high but this is moderated by availability of effective IPM strategies
that reduce the risk of inducing outbreaks and seasonal conditions that may not favour over
winter survival.
Taxonomy
Classification
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Chelicerata
Class: Arachnida
Subclass: Acari
Order: Acariformes
Suborder: Prostigmata
Superfamily: Tetranychoidea
Family: Tetranychidae Donnadieu (71 genera, 1200 species)
Tetranycidés Donnadieu, 1875
Tetrnychidae Murray, 1877
Subfamily: Bryobiinae Berlese (35 genera)
Bryobiini Berlese, 1913
Bryobiinae Reck, 1950
Subfamily: Tetranychinae Berlese (36 genera)
Tetranychini Berlese, 1913
Tetranychinae Reck, 1950
Name and Synonyms
Common Names:
Spider mites (various prefixes including two-spotted, pacific, desert, strawberry, carmine etc)
Scientific Name: Tetranychus lombardini Baker and Pritchard, T. turkestani Ugarov and
Nikolski, T. pacificus McGregor, T. desertorum Banks, T. piercei McGregor, T. gloveri Banks,
T. cinnabarinus (Boisduval).
Synonyms:
T. turkestani; T. atlanticus McGregor T. gloveri; T. tumidid Banks
Experts
Dr Owen Seeman and Dr Jenny Beard
Queensland Museum
PO Box 3300
South Brisbane 4101
Telephone 61 7 38407701,
Fax 61 7 3846 1226
E-mail [email protected]
Detection
Detection Method
Identification of spider mites generally relies on the shape of the male aedeagus, and correct
identification initially will require sending to an expert. It is important that collections include
some males if at allpossible.
Figure 2. This diagram illustrates the processes involved in the detection and identification of
spider mites
Symptom Description
Spider mites are the most dominant mite pests harboured by many agricultural and horticultural
crops and ornamental plants. Bolland et al. (1998) listed 3,600 species of plants world wide as
hosts of spider mites. Among these mites, the two-spotted mite, T. urticae, attacks more than 900
plant species including many plants with economical value.
Typical symptoms of spider mite damage are small yellowish-white spots on the upper side of
the leaf due to chlorophyll depletion, which may develop into irregularly shaped white or
greyish-white spots resulting in the yellowing and bronzing of leaves. Necrosis may occur in
young leaves and tender stems. Heavy infestation by some species may lead to leaves turning
brown, defoliation, or even death of the plant (Zhang, 2003).
Similar symptoms can be caused by thrips. Heavy infestations can cause yellowing or bronzing
of the leaves or even leaf drop, similar to drought stress. The main difference in damage
symptoms between spider mites and thrips damage is that thrips are usually associated with
irregularly shaped white or greyish-white spots distributed mainly along the mid-rib and side
veins of plant leaves (Figure 2); while similar symptoms caused by spider mites are distributed
randomly on leaves (Figure 3).
Figure 3. Thrips palmi damage to cucumber leaf.
Figure 4. Tetranychus sp. damage to bean leaves
Mites feed by piercing the plant tissue with their sharp stylet and then removing the contents of
cells, mostly from the spongy mesophyll. Each feeding event produces a small circle of damaged
cells, leaving a small white spot of damaged cells. With large numbers of mites or prolonged
feeding these feeding spots will eventually overlap, resulting in areas of intensively damaged
leaf. A bronzed colour is seen on the upper surface of the leaf corresponding to the damaged
areas on the underside. Heavily damaged plants may have mostly reddened or bronzed leaves
and may have considerable leaf loss.
Damage caused by mites reduces the photosynthetic capacity of leaves in cotton, thus reducing
the fruit carrying capacity of the plant. Extensive mite feeding eventually causes the leaf or fruit
to dry out, because of increased transpiration. Such leaves or fruit are then abscissed, resulting in
crop defoliation and loss of young fruit. It has also been suggested that mite saliva possibly
includes substances toxic to the plants, though this is still unclear.
In cotton the effect of spider mites on yield and fibre quality is related to the severity and
duration of the infestation. Severe spider mite infestations can reduce crop yields up to 90%,
with associated reductions in fibre quality.
Eggs are laid either directly onto the leaf surface or are attached to webbing produced by adults
from silk glands in their palpus (Jeppson et al., 1975). The webbing also has an important role in
mate finding, dispersal, interspecific relationships (e.g. strongly webbing species may displace
weakly webbing species), shelter and protection from natural enemies (Gerson, 1985). Prior to
moulting mites become inactive for a period. The inactive 'chrysalis' stages are known as the
proto-, deuto- and telio chrysalis respectively. Mites in the chrysalis stage are anchored to the
leaf surface with silk. At eclosion the exuvium splits dorsally. The mite frees itself from the
exuvium, which remains attached to the leaf surface (Crooker, 1985).
Adult male mites are able to locate the female teliochrysalis by chemical cues (sex pheromones)
which are believed to be associated with the production of silk used by the female deutonymph
to attach itself to the leaf. Females are generally mated as soon as they emerge from the
teliochrysalis, and although they may mate more than once, only the first mating is usually
effective. Sex ratios vary widely but are generally female biased with a ratio of approximately
3:1. This ratio normally decreases to 1:1 when densities are high. Reproduction is by
arrhenotokous parthenogenesis. Unfertilized eggs are laid by virgin and mated females and yield
haploid males. Fertilised eggs always yield diploid females.
Adult female T.urticae can survive winter as diapausing adult females or as actively reproducing
populations. The diapausing form facilitates survival in conditions where active forms would
perhaps perish and is therefore most prevalent in regions where winters are harsh and/or winter
hosts are scarce. The diapausing form is bright orange in colour, non-feeding, non-reproductive
and spends winter in sheltered locations such as crevices in bark, crotches of trees and in leaf
litter and soil at the base of trees. Diapause is induced in response to decreasing daylength (short
days) though the response is extremely variable. Temperature, and to some extent plant quality,
may also modify the response. In areas with mild winters mites can remain in the actively
reproducing summer form provided suitable hosts are available.
Sites of Infection/Infestation
Whole plant, leaves, stems, growing points, and inflorescence. Under side of leaves preferred,
but in heavier infestations other parts will be used. Diapause forms of some species may hide
under bark or increvices in plant material.
Spider mites have a preferred location on their hosts. Most spider mites feed on young leaves but
some feed on fruits and young stems. They may be found on the underside of leaves of host
plants, such as for the strawberry spider mite, or on the upper leaf surfaces of plants, such as for
the two spotted mite.
Identification
Morphological Methods
Morphological identification of spider mite species requires experience and specific technical
skills. Identification requires properly slide-mounted specimens and a compound microscope
with phase contrast and an interference system. Familiarity with taxonomic characters is very
important. Due to the lack of good diagnostic characters, some species are hard to distinguish by
external morphology. Alternatively, DNA analysis can be used to facilitate species identification.
Method - morphological identification
Materials and equipment
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Stereomicroscope
Compound microscope (with10x, 20x, 40x and 100x objectives)
Microscope slides and coverslips of #0 thickness
Oven set at 40-500C
Mounted micro-pins, glass excavated blocks and covers and fine pointed jewellers
forceps
Reagents
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Clearing agent:
o Nesbitt's fluid (chloral hydrate 40g; concentrated HCl 2.5ml and distilled water 25
ml);
o Kono's fluid (Chloral hydrate 100g; glycerine 10g; concentrated HCI 1ml and
distilled water 50ml)
Mounting medium
o Hoyer's medium (chloral hydrate 200g; gum arabic 30g; glycerine 20ml and
distilled water 50ml)
Sealant: Isonel or Glyptal
Oil immersion
Method
Clearing
Under the stereomicroscope, use a small brush to collect male and female adult mites and place
them in an excavated block containing drops of clearing agent (Nesbitt's fluid or Kono's fluid)
for clearing. Gentle heating (450C) in an oven for 20 minutes will accelerate clearing.
Mounting
1. Place a small drop of Hoyer's medium in the centre of a slide;
2. Place the mite in the medium and push the mite to the bottom of the medium with the aid
of mounted micro-pin: female mites should be oriented dorsoventrally with the legs
spread and male mites should be lying on its side
3. Lower a coverslip onto the drop and gently press the coverslip with a forcep
4. Circle the location of the mite under the slide with a marker pen and label the slide with
all collection information
5. Warm the slide in an oven at 45-500C for 2-4 weeks
6. Ring the edge of the dried slide with sealant applying one or two coats with a small brush
Examination
Under a compound microscope, follow taxonomic keys to identify the slide mounted mite
Results
1. The major taxonomic characters of spider mites (Tetranychidae) are:
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recurved long, whip-like chelicerae
thumb-claw on the palp tibia
eyes on lateral prodorsal
Taxonomic characters of subfamily of Tetranychidae:
Bryobiinae: female empodium with tenent hairs
Tetranychinae: female empodium absent, or if present without tenent hairs
2. Description of tetranychid species of quarantine concern, which are absent in Australia and
were studied in the scholarship training program.
The identification follows keys published by Seeman and Beard, 2005; Jeppson et al. 1975,
Zhang et al. 2000 and Wang, 1981.
Amphitetranychus viennensis: female peritreme branching; male aedeagus bent sharply dorsad
and the distal knob modified as a small anterior angulation near the base of the bent portion
Oligonychus shinkajii: female empodium clawlike with proximoventral hairs; dorsal body setae
longer than the distance between their bases; male aedeagus knobbed and bent dorsally
Panonychus ulmi: female empodium claw long and at right angles to the dorsoventral hairs;
dorsal body setae on strong tubercles coloured much lighter compared with rest of the body;
setae f2=2/3 f1; setae h2=1/3 f1
Schizotetranychus spp: female empodium clawlike split into 2 pairs without proximoventral hairs
1. S. bambusae: aedeagus broad basally, gradually curved dorsally with a blunt tip
2. S. nanjingensis: aedeagus gradually narrowing and slightly bent distally to form a
sigmoid shape
Tetranychus spp: female empodium with proximoventral hairs only or empodial claw when
present only a short spur; two pairs of h setae; peritreme hooked
1. T. piercei: female tarsus I with bases of 4 tactile setae proximal to the base of the
proximal duplex seta; male aedeagus weakly sigmoid, with shaft tapering to a pointed tip,
a distinct knob absent
2. T. truncatus: female empodia with a minute spur, tarsus I with bases of 4 tactile setae
proximal to the base of the proximal duplex seta; male aedeagus knob distinct and dorsal
margin with a medial indentation
3. T. turkestani: female tarsus I with bases of 4 tactile setae proximal to the base of the
proximal duplex seta; male aedeagus with the length of the posterior projection
approximately equal to the width of the most distal part of the main shaft, dorsal margin
of the aedeagus angulate.
Misidentification of similar pests in Australia
The accurate identification of spider mites is always a challenge due to a shortage of taxonomic
specialists as well as access to identification keys to species. An example of a misidentification
of spider mites occurred in Australia in 1929 when a species of spider mite was reported as T.
desertorum Banks, but later was determined as T. ludeni Zacher (Seeman and Beard, 2005).
Further Information
Contacts
Contact Points for further information
Dr Jianzhen Lin
Institute of Plant Protection
Fujian Academy of Agricultural Sciences
247 Wu Si Road, Fuzhou, China
E-mail: [email protected]
Professor Xugeng Sun
College of Plant Protection of Shandong Agricultural University
61 Dai Zhong Road, Taian, China
Telephone 86-538-8242988
E-mail [email protected]
Dr Owen Seeman and Dr Jenny Beard
Queensland Museum
PO Box 3300
South Brisbane 4101
Telephone 61 7 38407701,
Fax 61 7 3846 1226
E-mail [email protected]
Acknowledgements
The information displayed on these Spider Mite webpages was sourced from the Spider Mites
Diagnostic Scholarship Report (Zhang, L.) and the Spider Mites Pest Risk Review. These
documents were kindly provided by Office of the Chief Plant Protection Officer and Plant Health
Australia.
Lanni Zhang
Berrimah Farm - Makagon Road, Berrimah
GPO Box 3000, Darwin NT Australia 0801
Website: www.nt.gov.au/dpifm
Ph: 08 8999 2228
Fax: 08 8999 2312
References
Bolland, H.R., Gutierrez, J. and Flechtmann, C.H.W. 1998. World Catalogue of the Spider Mite
Family (Acari: Tetranychidae). Leiden, Brill. 392 pp
Gutierrez, J (1994) Acari - leaf feeding mites. In, Insect pests of cotton (G.A. Matthews and J. P.
Tunstall eds), CAB International, Wallingford, UK. pp 407-424
Jeppson, L.R., Keifer, H.H. and Baker, E.W. 1975. Mites Injurious to Economic Plants.
University of California Press, Berkeley, California. 614 pp
Leigh, T. F. (1985) Cotton. In, Spider Mites their Biology, Natural Enemies and Control. (Helle,
W. and Sabelis, M. W. Eds), Vol. 1B, pp. 349-358. Elsevier, New York.
Seeman, O. D. and Beard, J. J. 2005. National diagnostic Standards for Thetranychus Spider
Mites. Plant Health Australia National Diagnostic Standards Development (CD). Plant Health
Australia, Canberra
Wang, H. F. 1981. Acariformes: Tetranychoidea. Economic Insect Fauna of China, Fasc. 23
Yang, G. and Zhang, L. 1998. The IPM of snake bean, Vigna unguiculata ssp. sesquipedalis, in
the Top End of the Northern Territory. Proceedings of the sixth workshop for tropical
agricultural entomologists, Darwin. DPI&F Technical Bulletin No. 288, 95-100
Zhang, Z. Q., Zhang, Y. X. and Lin, J. Z. 2000. Mites of Schizotetranychus (Acari:
Tetranychidae) from moso bamboo in Fujian, Chian. Systematic & applied Acarology Special
Publications 4, 19-35
Zhang, Y. X., Zhang, Z. Q., Chen, C. P., Lin, J. Z. and Chen, X. 2001. Amblyseius cucumeris
(Acari: Phytoseiidae) as a biocontrol agent against Panonychus citri (Acari: Tetranychidae) on
citrus in China. Systematic & Applied Acarology 6: 35-44
Zhang, Z. Q. 2003. Mites of greenhouses identification, biology and control. CABI Publishing.
244 pp
Web links
http://www.lucidcentral.org/keys/v3/mites/Invasive_Mite_Identification/key/Tetranychinae/Medi
a/Html/Home_Tetranychinae.html
http://www.montpellier.inra.fr/CBGP/spmweb/index.php