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

PREDATORY MITES IN IPM
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of sex allocation, sex ratios approached half males, half females under random
mating, whereas a female bias was observed under sib-mating. It is suggested that
arrhenotoky is selected for when there is a substantial risk of high portion of
unmated females in the population: pseudo-arrhenotoky may evolve by
external/environmental pressure, since it retains the possibility to reinstall lost genetic
information in the maternally derived chromosome, by using the paternal chromosome
as a template for DNA-repair. This precise control of sex allocation in phytoseiids is
probably the significant mechanism by which these predators can regulate their
density, depending on both phytoseiid female and prey densities. They can in fact
adjust offspring sex ratio in response to the presence of conspecifics or their cues and
also to synchronize their population with that of prey (Nagelkerke & Sabelis, 1996).
The prediction of optimal sex ratio by means of modeling is selectively advantageous
when local mating groups vary in size and are usually small, as in the case of
experimental laboratory studies on phytoseiids. At a larger spatial scale than the local
mating group, the prediction appears to be less precise, may be due to operating and
interfering selection levels (Nagelkerke & Sabelis, 1998).
3.3. Life Style Types
The characterization and ranking of phytoseiid mites is a helpful and significant tool
(McMurtry & Croft, 1997), allowing a rating of species based on some
morphological, reproductive and developmental aspects. Furthermore, traits like
feeding and diet needs (McMurtry & Rodriguez, 1987; Schausberger & Croft, 1999)
and adaptation to certain foods (Castagnoli, Simoni, & Liguori, 2003), were
considered to ascribe the predators to the different life styles. McMurtry and Croft
(1997) considered that a four-types classification may be efficient to rank the
different species of phytoseiids and gave emphasis to the biological control of spider
mite pests (Table 2). However, new life style types might be identified.
Recent studies aimed at estimating/identifying the more significant traits
involved in phytoseiids rating and to possibly generate more stable classifications
(Croft, Blackwood, & McMurtry, 2004). The mainly and first exploited traits/factors
to rate phytoseiids were: (i) Feeding: the ability to prey and to feed on various prey
and other food types (McMurtry & Rodriguez, 1987; McMurtry, 1992), a primary
criterion considered for classification; (ii) External morphology: apparently, no
strong correlation was found between body size and generalist–specialist phytoseiids
(Schuster & Pritchard, 1963; Chant & Hansell, 1971) and more evidence is needed
to establish the association between body size and different life styles (Croft et al.,
2004); more correspondence was found in the evaluation of the adult dorsal shield
setal length, in association with the feeding specialization (Sabelis & Bakker, 1992).
Also, the mouthpart apparatus may be different between specialists and generalists
(Flechtmann & McMurtry, 1992), but it is not clear to what extent this could work
for a clear attribution to a life style; (iii) Biological parameters: research focused on
reproduction, development and mortality; the specialist phytoseiids generally show
intrinsic rates (Sabelis & Janssen, 1994) and sex ratio values higher than generalist
(Nagelkerke & Sabelis, 1996) as well as shorter developmental times (Luh & Croft,