Studies On The Biology And Activity Levels Of Carboxylesterase As An Indicator Of Insecticide Resistance In Populations Of Diamondback Moth, Plutella Xylostella (L.) (Lepidoptera: Plutellidae

ABSTRACT

Biology of Diamondback moth, Plutella xylostella (L.) (Lepidoptera:

Plutellidae) was studied in the laboratory under controlled conditions, i.e.

28 ±1 °C, 65-70 % r.h and a photoperiod of 12L: 12D hours. The results

indicated that the developmental time of P. xylostella from egg to adult

emergence took on the average 17.5 days. About 59 % of the eggs were laid

on the first night of oviposition. Additionally females were generally larger

(5.0mm) than males (4.5 mm).

Effects of temperature, pH, and substrate concentration on the hydrolysis of

a- naphthyl acetate by carboxylesterase from P. xylostella were evaluated.

Optimum ranges of these parameters were, 40-45 °C for temperature, 6 9-7.3,

for pH, and 35-40 mM for substrate concentration.

Carboxylesterase analyses of P. xylostella populations collected around Accra

indicated the probable incidence of insecticide resistance in the insect

population. Carboxylesterase activity levels ranged from 2.06 to 28.29 nmol /

10min/μg protein. While the highest activity was recorded by populations from

Kumoji Road and classified as moderately resistant, G.B.C (Ring Road) and

Legon populations were classified as highly susceptible. The finding has

enormous implications for the vegetable growers.

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