II.2. SQUASHES, PUMPKINS, ZUCCHINIS, GOURDS (CURCURBITA SPECIES) – 121
facilitation (Hurd, Linsley and Whitaker, 1971). Other bees, e.g. the honey bee
(Apis mellifera), also pollinate Cucurbita.
Phytophagous insects
In general, cultivated plant species are used as a food source by a large number of
phytophagous insects (e.g. Hodgekinson and Hughes, 1982; Hendrix, 1988), and the
Cucurbita are no exception, particularly in an agricultural setting. In addition to
chrosomalid beetles, other insects are known as pests of the cultivated Cucurbita species;
some of these have also been seen feeding from wild plants. These include
Epilachna spp. (Coleoptera: Coccinellidae) and Diaphania hyalinata and Diaphania
nitidalis (Lepidoptera: Pyralidae) (Mariano and Dirzo, 2002). See below for additional
information on common insect pests.
Plants in the genus Cucurbita have been shown to respond to herbivory in a number
of ways, e.g. in the production of flowers, fruits, pollen and pollen performance. Mariano
(2001) has observed such effects in C. argyrosperma ssp. sororia and C. pepo
var. texana. Ávila-Sakar, Krupnick and Stephenson (2001) have shown that the plants of
Cucurbita pepo var. texana are capable of reassigning resources destined for the
production of fruits and seeds to growth and production of staminate flowers as a
response to the removal of female flowers. Further, Avila-Sakar, Leist and Stephenson
(2003) have shown that C. pepo var. texana has a high tolerance of simulated herbivory;
low to moderate levels of foliar damage significantly affected very few traits. Finally,
Theis, Kesler and Adler (2009) in Cucurbita pepo var. texana showed that simulated leaf
damage increased fragrance production in male flowers. Female flowers which were
bigger and produced more fragrance than males flowers were unaffected by leaf damage.
These results suggest that changes in fragrance following herbivory may mediate
interactions between plants, herbivores and pollinators.
Plants
Anaya et al. (1987) and Anaya, Ortega and Nava Rodriguez (1992) suggest that the
effectiveness of Cucurbita species in weed suppression in traditional American
polyculture is due to a combination of competition for light and allelopathy. Qasem and
Issa (2005) reported that volatiles from C. pepo shoots may be phytotoxic:
soil-incorporated C. pepo residues prevented seed germination of P. oleracea and arrested
growth of other weed species tested (Qasem and Issa, 2005). In 2007, Fujiyoshi,
Gliessman and Langenheim examined the weed-suppressive properties of Cucurbita
interplanted with corn (Zea maize) by comparing different planting and weeding regimes,
and measuring weed biomass, light interception by crop canopy and yield. Shading by the
Cucurbita appeared to be the major mechanism of weed suppression, but the analysis
suggested that other factors, such as allelopathy, might also contribute.
Micro-organisms
Several types of viruses are known to attack the Cucurbita. The Mosaic viruses
(cucumber mosaic – CMV, watermelon mosaic – WMV, zucchini yellow mosaic virus –
ZYMV, and squash mosaic virus – SqMV) are the types most commonly observed in the
Cucurbita. These viruses are transmitted primarily by insect vectors (aphids) and the
primary approach to controlling the incidence of viral disease in cultivated Cucurbita is
control of the vector. The next section discusses the viruses known to infect the Cucurbita
in greater detail. The following section then briefly describes newer biotechnological