| dc.description.abstract | Recent concerns over possible human health problems and environmental damage resulting
from large scale application of chemical' pesticides for desert locusts control have led to
proposals for alternative control strategies. Biological control based on pathogens
formulated as biological pesticides is an alternative that offers more rapid prospects for
implementation. This study was conducted to investigate, under laboratory conditions the
effect of co-treatment of gregarious desert locust nymphs with phenylacetonitrile and low
doses of the fungus, Metarhizium anisopliae isolate ICIPE 21, with the aim of developing a
mycopesticide formulation.
The specific objectives of this study were: To determine median lethal dose (LD50)) and
median lethal time (LT 50) of, Metarhizium anisopliae isolate ICIPE 21; to assess the effect
of two different modes of application -of pheromone and fungus on insect mortality; to
assess the viability of .conidia in fungus-pheromone cocktail, and to investigate the
sublethal effect of the pathogen on reproductive potential of the surviving adults.
Conidia of Metarhizium anisopliae were formulated in aqueoussolution of Triton X-IOO or
in mineral oil while the pheromone, phenylacetonitrile (P ~N) was applied in mineral oil.
Experimental and control insects were maintained at 28 ± 2° C and 50-60 % relative
humidity throughout the experiment, Evaluations were carried out and fresh wheat
seedlings supplied as food daily.
The time required to kill 50% of the nymphs decreased significantly with the inclusion of
the pheromone, phenylacetonitrile. For instance, Metarhizium anisopliae alone at a
concentration, lxl0s conidia ml', had a median lethal time of9.4 days and upon inclusion
of PAN, it dropped to 6.2 days. The median lethal dose (LDso) of Metarhizium anisopliae
isolate lCIPE 21 was 6.5xl04 conidia ml'. The LTso values (time taken to attain 50%
mortality) for the fungus alone, ranged from 30 days for lx104 conidia mr! to 3 days for
the highest dosage of 5xl07 conidia mr! . The fungus -pheromone cocktail did not affect
conidia viability as it was maintained at 80% for a period of three weeks. The pathogen had
no sub-lethal effects on the reproductive potential of the surviving adults. There was no
difference in percentage hatchability of eggs between treated (67%) and untreated (74%)
females.
The results of this laboratory study demonstrate a complementation interaction between
phenylacetonitrile (PAN) pheromone and .low doses of M. anisopliae for control of
gregarious nymphs of Schistocerca gregaria.
These results are promising since they will lead to development of a fungus-pheromone
formulation for biological control of the desert locusts. | en |
