102 Papaya
several species of aphids in a non-persistent manner. This transmission is generally
characterised by a short acquisition access period (AAP) of a few seconds to min-
utes, absence of a distinct latent period and a short inoculation access period (IAP).
Thus, the virus is acquired during brief exploratory probes in the process of host
finding and is transmitted to a healthy papaya plant within a few seconds to min-
utes. Aphids do not normally colonise papaya and natural transmission is reported to
occur through transient aphid vectors.
9.4.1 Management
Seedlings raised under controlled conditions in net house significantly decrease
PRSV incidence. Removal and destruction of the affected plants is the only control
measure to reduce spread of the disease (Kumar et al. 2010). Aphids can be con-
trolled by application of carbofuran (1.0 kg a.i./ha) in the nursery bed at the time of
sowing seeds, followed by 2–3 foliar sprays of phosphomidon (0.05%) at an interval
of 10 days, starting from 15 to 20 days after sowing.
9.5 Scale Insects
More than five species of scale insects have been found on papayas, the most seri-
ous being the oriental scale, Aonidiella orientalis, which occurs on both fruit and
stem. So far, it is confined to limited areas. Recently other scale insects, Coccus
hesperidum, Aonidiella comperei, Selenaspidus articulates, Aspidiotus destructor
and Philaphedra tuberculosa have been reported (Martins et al. 2004). Scale insects
are not common on papaya trees but occasionally they build up in large numbers
to cause serious damage or death to the trees. Scales do not resemble typical insect
pests, so they often go unnoticed until a large population has developed and caused
damage. In the virgin land, scale insect has been most troublesome, apart from rats
and fruit-bats that attack ripe fruits.
Considerable damage may occur when large number of these insects feed upon
plants already weakened by environmental stresses, such as drought or disease.
Scales remove plant juices with piercing-sucking mouth parts. Some time, cer-
tain scale insects produce tremendous amounts of honeydew (an excess of liquid
and sugar expelled from their bodies). This sticky material may serve as a growth
medium for a sooty mold fungus. During large population build-up, some scales
become so abundant that an infested plant is totally encrusted with them. Three
types of damage to papaya plants are observed. Flower and leaf drop occur from
severely infested young plants. Infestation on seedlings or on young plants near
the apex observed, inducing distortion of apical leaves (Pena and Johnson 2006).
Finally the females get attached to the fruit causing cosmetic damage that makes
fruit unmarketable (Figure 9.4).
9.5.1 Management
The scale insect has at least nine different predators, among which the ladybird bee-
tle (C. montrouzieri) is the most important. It is also attacked by fungus Verticillium