Page 55 - Volume 2,Issue 2, July 2009

Katsarou

et al.

102

Asia that feeds on numerous aphid species

(1, 14, 24).

As there is lack of data on the toxic ef-

fects of insecticides against the above men-

tioned coccinellid predators, the aim of the

present study was to evaluate the residual

toxicity of one carbamate (methomyl) and

two neonicotinoids (imidacloprid, thiaclo-

prid) insecticides against the larvae (first and

third instars) and adults of three common

predacious coccinellids,

C. undecimnotata O.

conglobata

and

P. quatuordecimpunctata

.

Material and methods

Insects

Laboratory cultures of

C. undecimnota-

ta

were established from individuals collect-

ed in mid August 2006 from an alfalfa field

in the area of Arta (Epirus, south-western

Greece) and cultures

P. quatuordecimpunc-

tata

and

O. conglobata

were established

from adults collected during the same pe-

riod from a corn field in the same area. In

the area where the coccinellids were collect-

ed no insecticides had been applied for the

last five years. Ladybird beetles were reared

on broad bean plants (

Vicia faba

L.) infest-

ed with

Aphis fabae

Scopoli (Hemiptera:

Aphididae) and held in a controlled-envi-

ronment room at 23 ± 1

o

C, 65±5% r.h. and a

16-h photoperiod. F

5

progeny were used for

the experiments. Aphid colonies were es-

tablished from individuals collected from a

commercial bean crop (

Phaseolus vulgaris

L.)

and reared on

V. faba

plants.

Insecticide application

Five broad bean seeds were sown in

each pot (13.5 cm upper diameter, 7 cm

base diameter, 12.5 cm height and 1 l vol-

ume) filled with a mixture of peat (black and

white peat substrate, Floradur B fine, Flora-

gard) and perlite (Perloflor, Protectivo Ltd)

in a 6:1 weight proportion. When the plants

reached 20 cm of height they were spayed

with aqueous solutions of the insecticides

at the recommended doses and leaves were

collected 1 and 8 days after application. The

insecticides tested were: imidacloprid (Con-

fidor 200 SL, Bayer Hellas, 20% a.i., applied

rate 0.5ml/l), thiacloprid (Calypso 480 SC,

Bayer Hellas, 48% a.i., applied rate 0.3ml/l)

and methomyl (Selanox 20 SL, SEGE SA Hel-

las, 20% a.i., applied rate 1.5 ml/l).

Bioassay

Four leaves from the sprayed plants

were placed in each Petri dish (9 cm in di-

ameter) and the appropriate developmen-

tal stage of the predator was left to walk on

the sprayed leaves for 24 h. An opening was

made to the lid of the Petri dishes, which

was subsequently covered with fine mus-

lin to allow ventilation and maintenance

of humidity level inside the Petri dish sim-

ilar to that of the laboratory. For the larval

studies and in order to avoid cannibalism,

first and third instar larvae were placed in-

dividually in the Petri dishes. Groups of 10

larvae were considered as one replicate. For

the adult studies, five adults were placed in

each Petri dish and two Petri dishes were

considered as one replicate. First and third

instar larvae were exposed to insecticides

one day after their enclosure and adults

five days after emergence. After exposure

to insecticides, insects were placed in clean

Petri dishes and were provided with

A. fabae

daily. Larvae were checked daily until they

reached the adult stage. The adults were

also checked daily for 20 days following ex-

posure to insecticides and the dead individ-

uals were counted. Three to five replicates

were used for each insecticide and develop-

mental stage of the predator. The same pro-

cedure was followed for the control plants

which were sprayed with water.

Statistical analysis

Thedifferences inmeanmortality among

treatments were determined by the Mann-

Whitney U test using the statistical package

SPSS 14.0 (20).

Results and Discussion

Insecticides were highly toxic to both larvae