Beauveriabassiana, a biocontrol agent against the red palm weevil, Rhynchophorus ferrugineus larvae under laboratory and field conditions

Abstract EN

The presented study was carried out to assay the efficacy of a Beauveriabassiana(Balsamo) Vuillemincommercial formulation (Newfar) and its isolates against larvae of the red palm weevil Rhynchophorusferrugineus(Olivier).

Bioassay experiments took place to estimate theLC₅₀, LC₉₀, LT₅₀ and LT₉₀values.

By Newfar treatment, theLC₅₀'s against the 1^st, 5^th and 10^th larval instars of R.

ferrugineus were 0.078, 0.192 and 0.406 g/ml, respectively.

LC₉₀ values were 0.610, 2.030 and 4.547 g/ml, respectively for the 1^st, 5^th and 10^th instarafter 25 days of treatment.

Also, the LT₅₀values after using the concentration 1x10⁸ CFU's / 100mlwere 14.549, 16.167 and 21.022, days, respectively, while those of LT₉₀ were23.374, 31.196 and 99.344 days, respectively.

Whereas, 1 x 10⁸ CFU's / 100ml caused 95% mortality for 1^st instar, 85% for 5^th instar, and 65% for 10^th instar, 25 days after treatment.

The concentration 28 x 10⁶ conidia / 100ml caused 85% 65% and 55% mortality for1^st, 5^th and 10^th instar, respectively 25days post-treatment.

Additionally, five concentrations of both commercial formulation and isolates of conidial spores (1 x 10⁸CFU's / 100ml and 28 x 10⁶ conidia / 100ml) were evaluated against the 1^st, 5^th and 10^th larval instars of red palm weevil under laboratory and field conditions.

The results revealed that mortalities among treated larvae were significantly different than control, where no larva died among the control treatments.

The current study confirmed that the lethal action of B.

bassiana was directly proportional to the spore's concentration.

This study further confirmed that the earlier larval instars was more affected by B.

bassiana treatments than older ones.

The field study showed that infested date palm trees injected by New far formulation (B.

bassiana) at the site of infestation by the red palm weevil caused 80% recovery from infestation after 25 days from treatment.