INTERACTIONS AMONG THE ENTOMOPATHOGENIC FUNGUS, Cladosporium uridenicolla SPEG., AND TWO WHITEFLIES BENEFICIAL INSECTS, Eretmocerus mundus MERCERT AND Coccienlla undecimpunctata L.: FROM AN IPM PROSPECTIVE

Laboratory studies were initiated, for the first time, to evaluate the competitive
interactions among the entomopathogenic fungus, Cladosporium uridenicolla and the
two whiteflies natural enemies, the internal parasitoid, Eretmoeerus mundus and the
coccinellid predator, Coecinella undecimpunctata. The positive and negative effects of
these combinations in regulating the population of the silverleaf whitefly, Bemisia
argentifolii, were extensively studied.
The negative effects on the parasitoid were extremely low. No direct contact or
moralities occurred among the parasitoid population when parasitizing the nymphs.
Higher percentages of emerging parasitoid adults were also obtained. Meanwhile,
when Er. mundus adults were exposed directly to the fungal suspension, the mortality
percentage reached 5-7% only. Three to five days after treatment, B. argentifo/ii
nymphs were rejected as a host by Er. mundus adult due to the fungal growtti. The
majority of Er. mundus females also laid no eggs and no parasitism was detected.
 
The susceptibility of C. undeeimpunctata developmental stage'3 to C.
uridenieol/a varied according to spore concentrations and the treated life stages. Eggs
were more tolerant to the fungal infection, and hatchability reached 98.5%. The first
instar larvae of C. undecimpunetata were more sensitive to infection by C.
uridenicol/a, followed by the 2nd instar and pupal.
 
·Intra-guild predations were detected among the fungus and the predator,
because of the predator feeding on the infected SLWF nymphs. Their feeding rates on
the nymphs without mycelium varied between 38.65 and 56.5% for the larval instars
and adult stage. Meanwhile, when the mycosis appeared on the SLWF nymphs, their
feeding rates decreased sharply. Consequently, the pathogen could be considered as
the "intra-guild predator" which was directly able to infect the coccinellid predator in
the guild. In addition, C. undecimpunctata adults and larvae, that fed on the infected
nymphs by the fungus, became also as intra-guild predators of the pathogen.
Therefore, the use of both the fungus and the predator in combination had a
deleterious effect on the biological control of whiteflies and could minimize the control
efficiency. The control efficiency of the three natural enemies of B. argentifolii, when
used separately or in combination, varied according to the tested biological agent.
Using Er. mundus alone reduced the pest populations by 38.1%, whereas, C.
uridenieo/a shared by 19.4% in the pest population reduction. The interaction between
C. uridenieola and Er. mundus raised the control efficiency to 57.8%. The use of both
Er. mundus and C. undeeimpunctata in combination reduced the pest population by
38.7%. The three biological control agents combined together reduced the pest
population by 58.0%. Combination between both C. uridenieola and Er. mundus caused a
synergistic relationship (additive). The use of the pathogen in combinations with Er.
mundus improved suppression of B. argentifo/ii nymphs. Conversely, antagonism
relationship (non-additive) among the pathogen in combinations with the coccinellid
predator was detected. Therefore, the combination of C. uridenieo/a and whitefly
parasitoids require further studies in other systems. The results suggest that the
fungus and the parasitoid or the fungus and the predator may be used together for
IPM program of the whiteflies, which may lead to viable control options. The fungus
spore application should coincide with the later developmental stage of the parasitoid
or the predator developmental stages to pass the sensitive stages in order to
conserve these beneficial insects within the system.