Cicadas (Auchenorrhyncha) are very common insect in most terrestrial ecosystems
particularly agricultural areas. Many species are regarded as pests of cultivated
plants and can also be vectors of different plant diseases. Nevertheless, only
few surveys have been carried out in Tunisian agricultural areas on cicadas.
There have not been any comprehensive studies on cicada biology up to now in
Tunisian peach orchards (Najar et al., 1998;
Boukhris-Bouhachem et al., 2007; Chaieb
et al., 2011).
Peach trees exhibiting stunted shoots with small curled leaves were detected
in summer 2007 and 2008 in several orchards in northern Tunisia (Mornag). Leafhopper
provokes serious damage on young trees, in nurseries and on grafted plants.
Damage was hardly noticed in adult bearing trees. According to studies done
in affected orchards, a large number of adult and juvenile leafhoppers were
observed on peach shoots and on weeds (Chaieb et al.,
Among the diversified Cicadellidae family, the Typhlocybinae which represents
a very specialized group of minute insects, quite regular in shape and sizeable
range, often brightly colored and related with typical damage to plants (Grassi
and Dal Ri, 2006). Many cicadellids are phloem feeders but Typhlocibins
group feed on intracellular liquid of parenchyma cells because of their mouthpart
small size. This limited use of the plant is associated with typical injuries,
often mistaken with Thysanopteran or mite-feeding punctures, appearing as small
areas of depigmented cell clusters. These areas can turn brown with necrosis
and induce wider plant deformations (Nickel and Holzinger,
Recently damages similar to what previously described were observed on Tunisian
peach and almond trees. The leaves show discolored spots that became increasingly
necrotic. These symptoms can be confused with mite attacks. The feeding activity
induces alterations on plant tissues, especially on young, tender tissues on
the top of branches, inducing curled and twisted leaves. When the infestation
is particularly high, many new small leaves are produced. This feeding activity
causes alterations on plant tissues. Damaged leaves may turn yellow starting
from the margins and definitively dry and die (Chaieb
et al., 2011).
Leafhoppers biodiversity on peach trees in Tunisian North East were studied.
And Zygina flammigera were shown to be major species feeding on these
cultivated trees. A. decedens was previously reported on grapevine but
not as stone fruit pest, while Z. flammigera is new for the Tunisian
fauna (Chaieb et al., 2011).
The aim of this research was to study quantitatively the cicadellid populations in Northern Tunisian peach orchards ecosystem including cultivated plant, weed and edge.
MATERIALS AND METHODS
Study of cicadellid populations on weeds: For the quantification of leafhoppers we choose peach orchards with a dominance of weed specie. We used sweep net technique to collect leafhopper. Each sample was collected on linear distance of 30 m of a meter wide. This will allow us to reduce the number of leafhoppers captured per unit area and estimate the abundance of species or populations of leafhoppers on each plant host. At least three replications of 30 m-2 was done for each weed specie. Five principal species of Graminacea were investigated: Cynodon dactylon, Echinochloa laevita, Setaria verticillata, Hordeum murinum, Erigeron canadensis, 2 dicotyledonous associations: Chenopodiacea (Chenopodium album and Chenopodium murale) and Amaranthacea (Amaranthus retroflexus, Amaranthus hybridus and Amaranthus angustifolius).
Study of cicadellid populations on edge: The principal species of edge trees in Mornag was Acacia ebernua, Cupressus sempervirens and Tamarix aphylla. To estimate the population of leafhopper hibernating on each specie, we used yellow sticky traps during January 2009. Traps of 25x25 cm were placed in the canopy of each edge specie at 1.5 m height in the same farm. Traps were observed after one month and leafhopper cathed were counted. Three replications, for each species, were done.
Study of cicadellid populations on peach trees: Mornag, a severely impacted area with cicadellid damages, was chosen for field studies. Two techniques were used to investigate the leafhopper populations: sweep net and yellow sticky traps. One trap of 25x25 cm were placed in culture peach and at 1.5 m height. Leafhoppers were counted weekly and traps renewed monthly.
To verify leafhopper specie, tiny insects were collected in the net using a
mouth aspirator and were killed with ethyl acetate vapours and eventually dried
at room temperature until identification. Yellow traps were observed weekly
and renewed monthly from February to October and insects were unglued using
a paint brush and white spirit, then stored in alcohol until identification.
Morphological identification of the Typhlocybinae genus rely on the use of few
features, mainly color patterns, but can only be ensured by observation of the
male genitalia characteristic shape (Jmaes et al.,
2008; Demichelis et al., 2010). Hence, the
apical part of the male abdomen is cut and put for 12 to 24 h in 10% KOH solution,
then rinsed with water and observed in glycerine under stereomicroscope at magnification
x40 to x60. Identification is based on key of Faune de France (Della-Giustina,
Data analysis: Analyse of variance of data from study of leafhopper on weed and edge were done using ANOVA procedure, comparison of means is done by Duncan test using SPSS 11 software. Differences were considered as significant when p<0.05.
Study of cicadellid populations on weeds: The capture of leafhoppers per sweep net technique in weeds showed variability in the population depending on the species weed. Echinechloa and Setaria are most important reservoirs of leafhoppers. Captures of about 150 cicadelles/30 m-2 are observed in the case of Echinichloa. It is also interesting to note that the monocots are more receptive to leafhoppers than dicots (Fig. 1).
Study of cicadellid populations on hedge: Traps placed at canopy species used as a hedge show that some are covered by more than other leafhoppers, Acacia ebernua for exemple example seems to be a refuge for a large population of leafhoppers. Cupressus sempervirens and Tamarix aphylla do not seem to be a preference host plant for cicadellid (Fig. 2).
Study of cicadellid populations on peach trees: Monitoring of catches of the two main species of leafhoppers of fishing allows us to observe two periods of growth: The first period coincides with the beginning of peach vegetation activity, during this period we see the proliferation in number and limited in time. The population of both species seems similar. A second period comes around the beginning of May, during this period the spread of leafhoppers is more important in terms of number and spread over time. During this period there has been a proliferation of larger number of Asymmetrasca compared to that of Zygina (Fig. 3). In 2009, 1116 leafhopper were trapped, 82.2% Asymmetrasca and 15.9% Zygina, in 2010, 1218 leafhopper trapped: 78.8% Asymmetrasca and 19.8% Zygina. Other cicadellid species were trapped too but they have a very limited number (<2%), they are not be considered as peach pest and will not be studied here.
|| Mean number of leafhopper adults captured in 30 m2
of each specie of weed
||Mean number of leafhopper adults trapped in yellow sticky
trap on different edge species. Means with same letters are not significantly
different at p<0.05 (Duncan test)
|| Evolution of the number of captured A. decedens and
Z. flammigera during (a) 2009 and (b) 2010
Leafhoppers constitute an important pest for peach and other stone fruit species
in Mediterranean region. Important damage has been detected in different Prunus
spp. orchards during 1999 in Spain. Damage is attributed to the feeding
activity of leafhoppers (Homoptera: Cicadellidae) and is very important in growing
plants. The dynamics of these insects was followed between 1997 and 1999 in
five different orchards by means of three methods. The most important species
was Asymmetrasca decedens. It was abundantly collected in summer when
several peaks were observed. Only a single maximum of nymphs was detected. No
difference was found between orientations but a preference to grafted plants
was observed (Torres et al., 2000).
On peach tree leafhopper feeds on the sprouts causing serious damage to nurseries
and trees in formation. Asymmetrasca decedens has been identified as
the specie responsible for this damage. This leafhopper specie has been found
in other crops such as cotton, citrus, beet, in association with: Empoasca
decipiens et Empoasca pteridis. The leafhopper begins to enter the crop
in February-March, multiplying itself extraordinarily during the month of June
and decrease its activity in the following months. The optimum dates of treatment
are noted to be the first fortnight of June (nymphs), or the end of May (adults
before the laying of eggs) (Torres et al., 2000).
In Italy A. decedens Paoli and Z. flammigera are the commonest
leafhoppers infesting peach trees in Campania (southern Italy). A. decedens
can cause severe damage (leaf curling) mainly on young plants and leaves.
The percentage of infested shoots reached peaks of 54% (1989) and 80% (1990).
Adults migrate into peach orchards in April-May, from then populations develop
the maximum density in late July and after decrease. The eggs are deposited,
in general singly, in a wound produced in the main leaf vein. The apical leaves
of the youngest shoots and the medio-distal part of the leaf are the preferred
site for oviposition. The average number of young stages per shoot can reach
more than 2.5 individuals. Z. flammigera is very common, but net a pest
as A. decedens. This species is plasmophagous and cause silvering symptoms
on the infested leaves. (Viggiani et al., 1992).
Recently in Italy a study on 8776 cicadellid captured in peach show that 97%
are A. decedens and 3% are Z. flammigera (Viggiani
and Tesone, 2008). In Tunisia the percentage of Z. flammigera seems
to be more important than in Italy (19.8% in 2010 and 15.9% in 2009) (Chaieb
et al., 2011).
A. decedens is a polyphagous species which can feed important crops
such as beans, beet, cotton, citrus, grapevine, lucerne and potatoes. In recent
years, this species has been observed causing damage to peach trees in southern
Europe: Italy (Viggiani et al., 1992) and Spain
(Alvarado et al., 1994). Leafhopper population
can be increased with many factors: climatic conditions, the presence of alternative
food plants, cultural practices (fertilizers and irrigation), presence of natural
enemies. Adults of A. decedens usually overwinter in the shelter of evergreen
plants (citrus, for example) and reappear in spring. Although adult leafhoppers
can already be detected in February in peach orchards in southern Spain (Alvarado
et al., 1994), it is in May that their number increases. Eggs are
laid on the underside of leaves in June. They hatch about 2 weeks later and
the nymphs feed on leaf tissues for about 5 more weeks, passing through five
instars before reaching the adult stage. Nymphs are very active and move about
the foliage if disturbed but, unlike the adults, they cannot jump. This generation
is the one causing damage to peach in both Spain (Alvarado
et al., 1994) and Italy (Viggiani et al.,
1992). Eggs of a second generation are laid in August and a third one can
even occur depending on environmental conditions. It was precisely in August
that growers detected the damage in almond trees. Whether this corresponded
to the second generation or not deserves further investigation (Jacas
et al., 1997).
Leafhopper causes important damage on almond trees in Spain, insect exhibit
stunted shoots with small curled leaves have been detected in Spanish almond
orchards. Damage attributed to the feeding activity of leafhoppers (Homoptera:
Cicadellidae) could be detected during the summer. The dynamics of these insects
was followed in 1997 in three different orchards by means of yellow sticky traps
to monitor adult activity and by collecting young shoots to monitor immatures.
A. decedens was the predominant species. Leafhoppers were detected in
may but did not peak until mid July, when damage was conspicuous. Abundant catches
were observed during the whole summer. Contrarily, nymphs exhibited one single
maximum at the end of July. Any control measure against this pest should be
directed against this nymphal peak. In Spain a study on almond cicadellid show
that 85.2% are A. decedens, 11.6% Frutioidia bisignata and only
2.5% of Z. flammigera (Torres et al., 1998).
In Tunisia a study done on 2251 leafhoppers captured on almond show that 79.3%
was A. decedens and 19.3% Z. flammigera. The percentage of
Z. flammigera seem to be most important than in Spain (Chaieb
et al., 2011). It seem that in Tunisia except A. decedens and
Z. flammigera no other important species was detected.
In 2003, Asymmetrasca decedens was recorded for the first time on red
raspberry in Trentino, alpine region in the north-east of Italy. The damage
of this new pest was spectacular, especially on autumnal fruiting variety Polka.
Preliminary results of these surveys suggest that, on cultivated raspberry,
the pest may complete 2-3 generations in a season, from the end of May to the
end of October. The second generation is the most damaging on autumnal fruiting
varieties. During the season, part of A. decedens population may develop
on various spontaneous hosts too, from which adults may continuously migrate
towards the raspberry crops. The combined use of yellow sticky traps and visual
leaves inspections represent a valuable method to monitor the population development
of the pest on the crop and to time treatments correctly (Grassi
and Dal Ri, 2006). The period of adults activity in Tunisia seems to be
more important than in Italy and Spain. A. decedens and Z. flammigera
were trapped earlier since late February, in Europe this happen in May,
this can be attributed to more favourable climatic conditions in Tunisia. More
investigations are necessary in Tunisian peach orchards to propose such leafhoppers
Leafhopper constitutes serious threats to peach production and may have economic
importance as cited before in some Mediterranean countries. Preliminary observations
on the biology of cicadellids show that leafhopper, their cycle is closely related
to weed and edge. The survey of principal leafhopper on peach tree shows that
these last have a principal activity in summer between March and October. Further
bio-ecological studies should be conducted with deeper phonological analysis;
investigation of the interaction with beneficial fauna is necessary to implement
an adequate management program.
Thanks to Dr. Nusillard Benoit for his valuable recommendations. Thanks to Sadira company for providing study sites and help in trap installation.