Plant Virus Disease Spread Through Insect Vectors and Their Management 155
- Suitable adjustment of planting and harvest-
ing dates to avoid high-density populations of
vectors. - Breeding vector-resistant cultivars
Biological Control Methods
Although biological control by introduction of
predators and parasites of vectors is attractive for
economic and environmental reasons, it is not at
present very successful in virus control.
Chemical Control Methods
Use of chemicals remains the basic control mea-
sure for vectors of virus diseases but for maxi-
mum economic returns and in order to use them
only when needed, the epidemiology of the virus
and its vector needs detailed study.
Insecticides, particularly the systemic ones,
can sometimes efficiently control the spread of
circulative viruses because long acquisition and
inoculation feedings are required for transmis-
sion. On the other hand, pesticides hardly affect
the spread of NP viruses and may rather aggra-
vate the situation by enhancing vector manage-
ment and more sap sampling.
Mineral and vegetable oils and milk lipids
might inhibit NP transmission by modifying the
probing behavior responsible for transmission.
There, the physico- and electrochemical prop-
erties might insulate the secondary transduction
systems of insect feeding apparatus and inhibit
sap sampling (Simmons et al. 1977 ).
To prevent virus spread by insect, integrated
programmes have to be developed based on an
understanding of the biology and phenology of
the vectors and means of perpetuation of viruses,
adopting cultural control measures and minimum
application of the proper pesticidal formulations
at carefully chosen times.
Integrated Management of Aphid
Vectors vis-a vis PRSV (P)
The field experiment consisting of eight treat-
ments including control as well as synthetic and
plant-based chemicals with maize as border crop
was laid out in randomized block design at I. A.
R. I. Regional Station, Pune. The border crop of
maize was raised 15–20 days before transplant-
ing of papaya seedling. Starting 15 days after
transplanting till commencement of flowering of
plants, four applications of treatments as foliar
sprays were carried out at a fortnight interval.
Observations were recorded on 3rd, 7th and 14th
day after each application for number of migra-
tory aphids on five randomly selected plants per
plot from which mean number of aphids per plot
was worked out separately for each application as
well as pooled data. Similarly, numbers of plants
showing PRSV (P) symptoms were counted in
each plot at weekly interval to get the percent-
age of disease incidence after each application as
well as pooled data.Management of Aphid Vectors on
Papaya
After all the spray applications (Table 1 ), ex-
cept second application, the different treatments
showed significant effect in checking the aphid
incidence on papaya plants as compared to con-
trol plot receiving no spray application. Plants in
the plots with border crop of maize and treated
with fortnightly alternate sprays of dimethoate
(0.05 %) and azadirachtin (Nimbicidin 0.03 EC
4 ml/lt) were most promising in reducing the
aphid population on papaya plants. The average
effect of all the four sprays indicated significant
reduction in aphid incidence by different treat-
ments as compared to untreated control having
1.33 numbers of aphids per plant. The most sig-
nificant treatment of maize as a border crop with