Trioza apicalis

Bioforsk Rapport
Bioforsk Report
Vol. 5 Nr. 151 2010
The carrot psyllid, Trioza apicalis -
biology and control
Gulrotsuger, Trioza apiclis - biologi og
bekjempelse
Richard Meadow
Bioforsk Plantehelse
Forfatter, Bioforsk rapport nr. Side 1

Tittel/Title:
Hovedkontor/Head office
Frederik A. Dahls vei 20
N-1432 Ås
Tel.: (+47) 40 60 41 00
post@bioforsk.no
Carrot psyllid, Trioza apicalis - biology and control
Forfatter(e)/Author(s):
Richard Meadow
Bioforsk Senter
Bioforsk Division
Adresse
Postnummer og poststed
Tel.: (+47) 40 60 41 00
fornavn.etternavn@bioforsk.no
Dato/Date: Tilgjengelighet/Availability: Prosjekt nr./Project No.: Saksnr./Archive No.:
01.11.2010 Åpen 1110406 Arkivnr
Rapport nr./Report No.: ISBN -13-nr./ISBN-no: Antall sider/Number of
pages:
5(151)/2010 978-82-17-00707-4 Sider Vedlegg
Oppdragsgiver/Employer:
GA-FA Vestfold
www.gafa.no
Kontaktperson/Contact person:
Lars-Arne Høgetveit
lars-arne.hogetveit@lr.no
Stikkord/Keywords: Fagområde/Field of work:
Gulrotsuger, gulrot, bekjempelses strategier,
feller, alternative metoder
carrot psyllid, carrot, IPM, traps, alternative
control
Sammendrag:
Plantevern
Plant protection
Antall vedlegg/Number
of appendices:
Denne rapporten er en del av et forstudie som har som mål å finne frem til midler og metoder for
bekjempelse av gulrotsuger. Gulrotsuger er en alvorlig skadegjører der den slår til. Men utbredelsen
som viktig skadedyr er begrenset til Norge, Sverige og Finland. Den er også kjent som skadedyr i
noen få land lengre sør, som Sveits. Av den grunn har det vært få vitenskapelige undersøkelser og
det er lite som er kjent om artens biologi og adferd. Dette gjør det vanskelig å lage til bekjempelses
strategier som kan lykkes. Av de få studier som er gjort har noen gått grundig til verks, bl.a. Rygg i
1977. Rapporten gir en oversikt over det som er kjent om gulrotsugeren som kan bygges på med
videre forskning til å komme nærmere en vellykket bekjempelse.
Summary:
This report is part of a preliminary study with the goal of finding control measures and methods to
manage the carrot psyllid. The psyllid is serious pest in the areas it attacks. But its distribution as
an economic pest is limited to Norway, Sweden and Finland. It is also recognized as an occasional
pest in some parts of Central Europe, such as Switzerland. For this reason, there have been very few
scientific studies on this species and little is known about its biology and behavior. This causes
difficulty in designing successful management strategies. Of the few studies that have been done,
some have been very thorough as was the study by Rygg in 1977. The report gives an overview of
most of what is known about the carrot psyllid that can be used as a basis for further research
toward the goal of successful management of this pest.
Land/Country:
Fylke/County:
Kommune/Municipality:
Sted/Lokalitet:
Norge
Akershus
Ås
Ås

This report was commissioned by the Norwegian Agricultural Extension Service office GA-
FA Vestfold and is financed by GA-FA, Fylkesmannen i Vestfold and Gartnerhallen AL. The
background for the commission was the extreme difficulty in controlling the insect pest
Trioza apicalis, the carrot psyllid or carrot sucker. As a result of ineffective control, the
carrot psyllid causes damage and losses amounting to millions of kroner each year in the
regions of attack.
Distribution, Biology and Life-cycle
In Norway, the regions with reported attack of the carrot psyllid are southeastern and
eastern Norway from Aust-Agder to Hedmark as well as some areas in Nord-Trøndelag. This
distribution does not appear very different from the assumed distribution reported by Rygg
in 1977.
In addition to Norway, the carrot psyllid has long been the cause of damage of economic
importance annually in parts of Sweden and Finland (Nissinen et al. 2007; Nehlin et al.
1994). It is also known as an occaisional pest in central Europe, including Switzerland
(Láska 1974; Burckhardt & Freuler 2000). Because of its relatively limited importance
outside the Nordic countries, the carrot psyllid has been the subject of very little study in
the scientific community. This report collects the current knowledge of the carrot psyllid
in relation to controlling the pest and limiting the damage it causes to the crop, with the
aim of providing a basis for further studies to help alleviate this pest problem.
The carrot psyllid has one generation per year. It tolerates cold climates and is unharmed
by winter temperatures of -18°C (Rygg 1977) and possibly as cold as -30°C (A. Nissinen
pers. com.). It overwinters in the adult stage in coniferous trees, preferably Norway spruce
(Láska 1974, Rygg 1977). This preference was confirmed in a recent study in Sweden where
only a few individuals were found on pine, yew, thuja or other conifers, while the greatest
proportion (over 80%) were in Norway spruce (Kristoffersen & Anderbrant 2007). In the
same study, carrot psyllids were found as far as 1 km from carrot fields. The maximum
distance that the carrot psyllid can fly is not known.
The adult carrot psyllids (fig. 1) leave their winter host in late spring, usually at the time
when the main carrot crop is emerging. Observations in recent years in southern
Lågendalen in Norway, an area with high populations, indicate that immigration began the
last week in May (L.-A. Høgetveit pers. com.). It is currently unknown which cues initiate
the carrot psyllid's migration from its winter host to its summer host. It is likely that it is a
combination of daylength and the quality of the winter host as a nutritional source, as is
the case for migratory aphids. Immigration into carrots often occurs at roughly the same
time as emergence of the carrots from the soil. Rygg (1977) found that there was a higher
rate of flight on days with higher temperature and more hours of sunshine. Both males and
females are found in carrot fields and the assumption is that carrot psyllids mate on
carrots (Kristoffersen & Anderbrant 2007).
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Fig. 1. Adult carrot psyllid. Photo: Bioforsk
The carrot psyllid also has a strong preference concerning its summer host. Studies have
shown that it chose carrot over other host plants (Rygg 1977; Nehlin et al. 1996). Rygg
also found that the carrot psyllid could not complete its development on other hosts he
investigated. In other studies, where the females were not given a choice of host plants,
they layed eggs on several species related to carrot and the larvae were able to develop on
most of these (Valterová et al. 1997).
When the adults have settled on the carrot plants they begin feeding. They feed by
inserting a stylet into the plant tissue (Hodkinson 1974) and suck nutrients from the
phloem. Feeding by carrot psyllid causes curling of the youngest leaves (fig. 2), not
necessarily directly at the feeding site. This is assumed to be the result of a toxin that is
transported systemically in the plant causing other symptoms, including wilting and death
of the plants (Markkula & Laurema 1971). The toxin is unknown, but recent studies have
shown an association between the carrot psyllid and the plant pathogenic bacterium
Candidatus Liberibacter solanacearum (Munyaneza et al. 2010). In a Norwegian study, a
trained test panel conducted sensory tests of carrots with different levels of carrot psyllid
damage (Seljåsen et al. 2006). They found that plants with heavy attack early in the
growth period yielded carrots that had negative taste characteristics, including bitterness
and astringency, and that the carrots were tough and lacking crispness.
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Fig. 2. Leaf curling caused by the carrot psyllid. The leaflets at the top are mostly unaffected.
Photo: Bioforsk
The females place the eggs in the leaf tissue, protruding from the edges of the leaves
(fig.3). The nymphs continue the feeding process through 5 stages which last through most
of the summer. The new generation of adults feeds for a period on the carrots before
migrating to the winter host.
The carrot psyllid is very difficult to control using currently registered insecticides.
Growers in Norway have reported poor efficacy when using pyrethroid insecticides against
the pest. Although DNA tests have not been able to confirm genetically based resistance
(Nordhus et al., 2006), the poor effect seems to indicate that the carrot psyllid has
developed resistance against this group of insecticides. This is not unlikely, as evidenced
by the development of insecticide resistance in the carrot psyllid's close relative, the pear
psyllid (Psylla pyricola) (Burts 1989).
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Fig. 3. Carrot psyllid eggs in leaf and petiole. Photo: Lund University
Living or Non-living Mulch
Based on reports from the 1930s that sawdust among the plants reduced attack by carrot
psyllid (Apsits 1931), studies were conducted in Sweden using different amounts and
application intervals of sawdust. The results confirmed the earlier reports, with a great
reduction in egg-laying and damage to the plants in all of the treatments with sawdust
(Rämert 1993). It appears that the monoterpenes in sawdust from spruce or pine has a
repellent and/or confusing effect. Both fresh sawdust and sawdust treated with turpentine
or monoterpenes greatly reduced damage to carrots from the carrot psyllid (Nehlin et al.
1994). In a study in Norway in the mid-1990s, carrots were grown either by conventional
agronomic practice or in an intercrop or with a mulch of either sawdust or plant material.
There was also a treatment combining an intercrop between beds and a sawdust mulch in
the beds (fig.4). The results showed a significant reduction in the number of plants with
carrot psyllid eggs in all of the treatments with mulch or intercrop (fig. 5). The greatest
reduction was in the treatment with intercrop (vetch) between the beds and sawdust in
the beds (Aas 2000; Brandsæter et al. 1999).
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Fig. 4. Research plots to compare the attack of carrot psyllid on carrots surrounded by bare soil,
intercrop, plant mulch, sawdust mulch or a combination. Photo: Bioforsk
Fig. 5. The percentage of plants that had carrot psyllid eggs when grown in bare soil or surrounded
by an intercrop of hairy vetch or with mulch. (Source: Aas 2000)
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Crop Covers
The most effective and most commonly used non-chemical method to control carrot psyllid
and other insect pests of carrot is to cover the crop with insect net or other covers.
Because of the psyllid's small size the netting must have a fine mesh. If the crop is covered
from emergence until the main flight period is done, the carrots should be well protected
from attack. When applying the netting at emergence it is important that the carrots are
sown in depressions of at least 5 cm so the newly emerged plants are not physically
damaged by contact with the net. One problem with this method is the extra labor and
exposure to attack when removing the covers to allow for mechanical weed control
(herbicides can be applied through the netting). Another problem is the change in
microclimate, with both higher humidity and higher temperature. The higher humidity
encourages plant diseases. The higher temperatures (as high as 64° C has been recorded)
cause physiological disorders and negatively affect the quality of the crop.
Exclusion Fences
Fences made of insect netting have been successful in keeping some insect pests out of
vegetable fields. This method was developed especially for low-flying insects such as
cabbage and turnip root flies (Delia spp.)(Meadow & Johansen 2005). Kristoffersen and
Anderbrant (2007) found adult carrot psyllids up to a height of 4 meters above the ground
in spruce trees. In Rygg's studies (1977), there were only small differences between traps 8
cm or 70 cm above the ground in numbers of adult carrot psyllids migrating into the field.
Both of these studies tend to negate the probability of fences being effective to keep
carrot psyllids out of carrot fields. A netting impregnated with insecticide, currently in use
worldwide for protection from and control of mosquitoes, has been developed to protect
vegetable crops from insect pests (fig. 6). Produced by Vestergaard-Fransen under the
tradename Fence ® , the netting is intended to both exclude certain insect pests and
through its attractive color and insecticidal effect, it reduces the pest population by way
of "trap and kill". This type of fence might be a tool in an integrated strategy against the
carrot psyllid.
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Fig. 6. Exclusion fence with attractive color and impregnated with insecticide. Photo: Bioforsk
Monitoring
Monitoring is an important tool to give the grower information on the time of attack. In the
case of the carrot psyllid it is the adult migration from the winter host to the summer host
that is crucial. If the grower has an insecticide to use, it should be applied in time to
control the adults before they feed on the carrot plants. By the same token, if the grower
is using insect net or other covers it is important to cover the plants before invasion and
also to know when it is safe to remove the covers. The carrot psyllid is currently monitored
using the same yellow sticky-traps (fig. 7) as are used for carrot fly (Psila rosae). No
studies have been done to test the optimal color or optimal placement of these traps. A
study in Finland where the crop was exposed to carrot psyllid attack at different times in
the flight period, to give different attack levels, concluded that one carrot psyllid adult
per trap (5 traps per hectare) was correlated with economic damage (Tiilikkala et al.
1996). Researchers in Switzerland currently use the yellow sticky-traps in an extension
strategy to indicate when the first adult carrot psyllids come into the field. The growers
are informed at the start of the attack and follow up by observing 20 plants at 10
reference points in the field for curling damage (Fischer & Terrettaz 2002; S. Fischer pers.
comm.). These observations are compared to treatment thresholds to determine whether
or not to apply insecticide.
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Fig. 7. Yellow sticky trap for monitoring flight activity of the carrot psyllid. The vials near
the top of the post are experimental dispensers for attractants. Photo: GA-FA Vestfold
To inrease monitoring efficiency, research has been done to identify the plant components
that are attractive to the carrot psyllid. Swedish studies found two components that were
present in high amounts in attractive plant species, sabinene and alpha-pinene (Nehlin et
al 1996). They also found that species with high amounts of another component, limonene,
were very unattractive to adults of the carrot psyllid. The attractive components have
since been studied to enhance trapping, but so far without success. The unattractive
components have been tested for repellent effect which appears to reduce attack when
applied in high amounts (Nehlin et al. 1994). It is likely that the repellent effect is due to
the predominance of these compounds in the winter host, spruce. Since the adults have
received cues to leave the spruce and seek out carrot, it is reasonable to conclude that
they are repelled by the odor of the winter host.
Future Prospects
Because the carrot psyllid is a pest of a small crop there is little (or no) investment by
international pesticide companies to find insecticides for this pest, neither chemical
compounds nor biological control agents. There are few closely related pest species on
closely related crops, so the possibilities for off-label registration of insecticides against
carrot psyllid are also very limited. Since damage is initiated by attack of overwintered
adults on small plants, an insecticidal control has to be quick acting. The most likely
candidates should have a contact effect and/or be systemic in the plant, since the psyllid
feeds from the plant phloem. Of the synthetic insecticides, ones with new chemistries will
help avoid problems with resistance. Spirotetramat (trade name Movento) is one such
insecticide that has a good effect against sucking insects, including psyllids (Brück et al.
2009).
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Biological control agents will probably have most effect against the nymphs of carrot
psyllid. Their biggest contribution in a management strategi will likely be to reduce
populations in a region to improve the situation for the following year. A strain of the
insect pathogenic fungus Paecilomyces (=Isaria) fumosorosea has been shown to have a
good effect against the Asian citrus psyllid Diaphorina citri, a major pest of citrus that has
threatened the Florida citrus industry (Avery et al. 2009; Hoy et al. 2010). P. fumosorosea
non-specific and is also native to Norway, so this fungus could be a candidate for further
investigation as a tool in an integrated management program.
As this report has shown, much research remains to be done to have a better
understanding of the biology and behavior of the carrot psyllid in order to develop an
effective management strategy. In terms of more basic research, we need to investigate
the response of the carrot psyllid to plant odors and pheromones. Finding the most
attractive odors will provide a tool for monitoring, trap-and-kill and push-pull strategies.
Further studies on repellant odors such as the monoterpenes, will help us to keep the
carrot psyllid from finding the carrot host plants and can also be utilized in push-pull
strategies.
Studies on the carrot psyllid's migration behavior will shed light on the alternative hosts
that it utilizes after leaving the winter host (spruce) until it arrives on the summer host
(carrot). This knowledge will provide the opportunity to monitor the pest before it begins
feeding on the crop and give the growers time to protect the crop.
Applied research also needs to be done. Methods need to be developed for protecting the
crop from attack, including directly reducing the population of the carrot psyllid. New
insecticides need to be tested for their effect on controlling this pest. Biological control
agents should be included in such tests. Ways to physically prevent the psyllid from
reaching the plants, such as exclusion fences, should be further studied. Dependable
methods, such as crop covers of insect netting need to be optimized to give maximum
protection without undue negative effects on crop quality.
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Thesis. The Agricultural University of Norway 69 pp.
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