 Aphids
- the ultimate vector
Aphids damage cucurbits in three ways:
- by direct feeding,
- by contamination with excrements,
and
- as vectors of viruses.
Aphids insert needle-sized sylets through
the skin to feed on phloem in the underlying tissue. Infection is
immediate - a few seconds of probing is all that's needed to acquire
the virus. This vector-aphid relationship is called non-persistent and
is characteristic of ZYMV,
WMV-2, PRSV and CMV.
The aphid's probing results in damage from
the removal of photosynthate needed to fill developing fruits. Aphids
also feed on the lower surfaces of the leaf, causing a downward
cupping of the leaf. This cupping forms a protected area in which
aphids can continue to feed and reproduce because insecticides can't
penetrate the cupping areas. Three aphid species colonize cucurbits
and can cause damage:
- the melon aphid, Aphis gossypii,
- the green peach aphid, Myzys
persicae, and
the cowpea aphid, Aphis craccivora.
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