[Edited_by_A._Ciancio,_C.N.R.,_Bari,_Italy_and_K.(Bookos.org)

CLASSICAL AND CONSERVATION BIOCONTROL
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guidelines (Aucejo et al., 2003). More recently, studies are underway to ascertain the
usefulness of banker plants as a source of aphid parasitoids in citrus, using the same
strategy already in use in protected crops (Calvo & Urbaneja, 2004). Barley plants
infested with cereal-specific aphids, such as Rhopalosiphum padi (L.), parasitized by
aphidiine parasitoids, such as Aphidius colemani Viereck, are produced by
commercial insectaries and introduced into the orchards before citrus aphid
populations peak during early spring. This strategy could prove very useful when
grassy covers [e.g. Festuca arundinacea Schreb (Poales: Poaceae), see below]
providing food to these specific aphids are also used.
5.3. Ground Cover Management Strategies
Spanish citrus orchards are quite commonly grown on bare soil by either use of
herbicides or mechanical means. This is not the ideal situation and the use of a cover
crop as an ecological infrastructure (Boller, Häni, & Poehling, 2004) is encouraged
by IPM guidelines. However, little is still known about the fauna inhabiting this
stratum in citrus and the ecological relationships occurring between the ground and
the tree arthropodofaunas. Therefore, the ground cover management is being
investigated at this moment as a means of conserving ground-dwelling natural
enemies and enhancing their impact on some citrus pests (top-down control), as well
as a means of providing bottom-up control of these pests. This is the case of both
T. urticae and C. capitata.
Tetranychus urticae is a serious problem in clementine mandarins in the Eastern
coast of Spain. Infestations downgrade fruit and, because T. urticae can feed on
more than 900 plant species (Bolland, Gutiérrez, & Flechtmann, 1998), cover crop
management can dramatically affect the dynamics of T. urticae populations on the
trees. In 2003, a survey of the acarofauna associated to the most common weeds
appearing in citrus orchards showed that Poaceae presented the lowest ratio
T. urticae/Phytoseiidae from the 45 weed species studied (Aucejo et al., 2003).
Therefore, a cover of Festuca arundinacea Schreb (Poales: Poaceae), a grass that
had been previously selected as a citrus ground cover for other agronomic favorable
characteristics, has been compared to a wild cover and to bare soil during the last 2
years (2006–2007).
The results obtained so far show that the F. arundinacea-sown cover has resulted
in the lowest populations of T. urticae on the trees and could consequently be
recommended to growers. The mechanisms explaining these results could be related
both to a host-feeding specialization by T. urticae (bottom-up control) and to the
composition of the beneficial acarofauna associated to the ground cover (top-down
control), which resulted more diverse and balanced on both F. arundinacea and the
trees grown on that particular cover than on both the wild cover and the bare soil
systems (Aguilar-Fenollosa, Pascual-Ruiz, Hurtado-Ruiz, & Jacas, 2008, 2009). In
addition to T. urticae, other citrus pests spend part of their life cycle on the ground
cover, such as aphids, or in the soil, like C. capitata, which pupates in it. In recent
years, different groups of ground-dwelling predators have been catalogued in
Spanish citrus orchards (Monzó et al., 2005; Urbaneja et al., 2006). These studies