Effect of Vegetation Height and Cover on the Viability of Metarhizium acridum Conidia Used in the Control of the Desert Locust Nymphs (Schistocerca gregaria) (Forskål)

Abstract

The effect of plant height and density of vegetation cover
(millet) on the efficacy and residual effect of Metarhizium acridum
conidia (Green Muscle®) in controlling Desert Locusts was evaluated in
semi-field conditions inside large cages of 2x2x1 m. A mixed population
of third (L3) and fourth (L4) instars of nymphs was used as target. The
study was organized in two trials, separately carried out according to the
plants height: Trial I, on short vegetation (27-37 cm) and Trial II, on tall
vegetation (73-93cm). In both trials, the insects were treated in two
different vegetation covers: low (~10 %) and high (~100 %). A dose rate
of 2.5 x 1012 conidia/ha was used with two different application volumes:
1 and 2 L/ha. The efficacy of the biopesticide was evaluated by mortality
rate of treated nymphs followed during two weeks. On the other hand,
untreated nymphs released in cages with treated vegetation were used to
evaluate the effect of residual conidia in the two different vegetation
states. No significant influence of vegetation cover on the efficacy of
Metarhizium was observed in short vegetation (p = 0.828) or in tall
vegetation (p =0.334) when a volume rate of 1 lire per hectare was used.
In high vegetation cover, the increase of the applied volume rate to 2 liters
per hectare significantly improved mortality rate. Also, conidia were alive
six days after treatment with good effect on untreated nymphs released on
treated vegetation. For the same period, no residual effect was observed in