Page 13 - Volume 6, Issue 2, July 2013

© Benaki Phytopathological Institute
Papanikolaou et al. 60
Type II functional response seems to be
common among aphidophagous coccinel-
lidae species. Thus, a type II functional re-
sponse is recorded for Cheilomenes sulphurea
Olivier male adults on Aphis fabae Scopo-
li (Hodek et al. 1984), Coelophora inaequalis
F. fourth instar larvae and female adults on
Toxoptera citricida Kirkaldy (Wang and Tsai,
2001), Propylea dissecta Mulsant fourth in-
star larvae and adults on Aphis gossypii Glov-
er (Omkar and Pervez, 2004), Harmonia axy-
ridis Pallas larval instars and female adults on
Myzus persicae Sulzer (Lee and Kang, 2004),
Coccinella septempunctata L. fourth instars
and adults on M. persicae (Cabral et al., 2009),
H. axyridis and C. septempunctata third in-
star larvae and adults on Aphis glycines Mat-
sumura (Xue et al., 2009), Hippodamia var-
iegata Goeze larval instars and adults on A.
fabae (Forhadi et al., 2010) and Adalia bipunc-
tata L. female adults on M. persicae (Jala-
li et al. , 2010). However, few exceptions have
been reported, as Messina and Hanks (1998)
showed that plant architecture may alter the
type of functional response of P. quatuor-
decimpunctata L. fourth instars and adults,
where Lou (1987) reported type I and Hu et
al. (1989) type III functional responses for
Harmonia axyridis Pallas adults.
Coccinellids’ handling time, i.e. the time
a predator spends on pursuing, subduing,
eating and digesting its prey, is not constant
through functional response experiments
(Hassell et al. , 1976). Hodek (1996) stated that
hungry aphidophagous coccinellids com-
pletely devour the first prey items they en-
counter and then become less competent at
exploiting prey. According to Papanikolaou
(unpublished data) this trait results from the
digestion process. Nevertheless, the estima-
tion of handling time based on mean values is
substantial for developing general models for
the description of density-dependent preda-
tion in a realistic manner (Hassell et al., 1976).
In a previous study, Papanikolaou et al.
(2011) showed that larval instars of P. quatuor-
decimpunctata exhibit a type II functional re-
sponse on A. fabae, when allowed to prey for
24 h. The present study investigated the func-
tional response of the predator on A. fabae at
12 h taking into account that handling time
is not constant through functional response
experiments. Furthermore, the appropriate
model was fitted to the data in order to pre-
dict the predation ability of P. quatuordecim-
punctata on several densities of A. fabae.
Materials and Methods
An A. fabae colony (originally from a stock
colony from the Biological Control Laborato-
ry, at the Benaki Phytopathological Institute)
was reared on potted fava bean, Vicia faba
L., plants at 20 ± 1ºC (65 ± 2% RH, 16:8 (L:D)
h). Propylea quatuordecimpunctata was col-
lected in summer 2006 from corn, Zea mays
L., plants infested by the corn leaf aphid,
Rhopalosiphum maidis Fitch, in Arta Coun-
ty (Northwestern Greece, 21°0’0’’/39°10’0’’)
and was reared on A. fabae in cylindrical
Plexiglass cages (50 x 30 cm) at 25 ± 1ºC, 65
± 5% RH and a photoperiod of 16:8 (L:D) h.
Functional response experiments were
carried out at 20 ± 1°C, 65 ± 2% R.H., with a
photoperiod of 16:8 (L:D) h. The experimen-
tal arena consisted of a plastic container (12
cm height x 7 cm diameter) with a potted V.
faba plant (top growth was cut in order to
provide plants of 8-9 cm height), bearing
different densities of A. fabae (3-3.5 day-old
immature aphids to avoid reproduction dur-
ing the experiments). A single predator lar-
va of a certain instar, which was previously
starved from food for 12 h, was placed into
the experimental arena for 12 h. The prey
densities tested were 2, 4, 8, 16 and 32 aphid
nymphs for the 1st instar larvae of the pred-
ator, 2, 4, 8, 16, 32 and 64 nymphs for the
2nd instar larvae, and 4, 8, 16, 32, 64 and 128
aphids for the 3rd and 4th instar larvae.
In order to test for density-dependent
prey mortality, a logistic regression analy-
sis was conducted on the proportion of prey
eaten as a function of the initial prey densi-
ty, fitting the polynomial function (Juliano,
2001):
)NP NP NP P exp( 1
)NP NP NP P exp(
N
N
3
0 3
2
0 2 0 1 0
3
0 3
2
0 2 0 1 0
0
e
+ + + +
+ + +
=