54
The use of
B. popilliae has proved remarkably successful. Between 1939 and 1953 over 100 tons
of spore powder were applied to turf in over 160,000 sites in the USA as part
of a Government
programme (Fleming, 1968). Larval numbers in the turf were reduced 10- to 20-fold and the
population stabilized at this new low level, with corresponding reductions in the levels of adult
beetle damage. However, the treatment is most effective when applied on a
region- or state-wide
basis (or at least to relatively large areas) to reduce overall the levels of beetle infestation. It is less
appropriate for use by small landowners, who may control the larvae in
their own turf only to find
their trees and shrubs being eaten by beetles from their neighbours' properties. Also, because
B.
popilliae is obligately dependent on its hosts for sporulation and because some larvae may not
ingest spores (or not ingest enough to cause disease) a periodic resurgence and decline of the
pest problem can be expected. The success of the control programme must be judged not on this
basis but by the fact that over a number of years the mean level of pest
damage is lower than it
would be in the absence of
B. popilliae.
Advantages and disadvantages of B. popilliae
The advantages of
B. popilliae include (1) its very narrow host range (which is environmentally
desirable) and its consequent lack of effect
on beneficial insects; (2) its complete safety for man
and other vertebrates (for example, it does not grow at 37
o
C); (3) its compatibility with other control
agents including chemical insecticides and, more recently, insect-pathogenic nematodes (Thurston
et al., 1994); (4)
its persistence, giving lasting control.
Its disadvantages, however, include (1) the high cost of production
in vivo; (2) its slow rate of
action; (3) most importantly, its lack of effect (etkisinin olmaması, etkisiz olması) on adult beetles
which often cause the most obvious and distressing (Tehlikeli, Endişe verici) damage, and (4) its
relative unattractiveness to the small landowner. Ni
speten cazip olmaması
Outstanding problems
There is evidence that the Japanese beetle has re-emerged as a serious pest in
some regions
where it had been controlled effectively since the initial applications of spore dust in the 1940s
(Dunbar & Beard, 1975). Larval densities ranged from 0 to 474 per square metre of turf in 1974
(mean 112), and were sometimes as high as those recorded 25 years earlier, before the control
programme was begun. Moreover, in this study only 0.2% of larvae collected from field sites
showed symptoms of milky disease compared with 41.5% disease incidence in a survey in 1946
after
B. popilliae had been introduced. Spores collected from these
few diseased larvae caused
only 7 to 17% infection of larvae in laboratory tests, compared with 65 to 67% infection from spores
collected from New York State where a decline in the degree of control had not been reported.
Even this figure was low in relation to the expected 90% disease incidence at the inoculum level
used. Perhaps there has been a reduction in virulence of
B. popilliae in
field sites over the years,
coupled with an increased degree of resistance of the target pest (see Redmond & Potter, 1995).
This might be expected by natural selection, because an obligately pathogenic bacterium that kills
its host too rapidly would be at a selective disadvantage.
5.1.2. Funguslar
Fungusların bulaĢtığı böcekler hastalanarak çok kere kısa ya da uzun bir süre
sonra ölürler. Fakat funguslar, orman böcekleriyle savaĢta baĢarılı sonuç vermezler.
Çünkü, asalak funguslar oldukça sıcak ve nemli koĢullarda böcek afetlerine karĢı
etkili olurlar. Bunun sonucu olarak, funguslara gereksinim duyulduğu epidemilerde,
mevcut nem oranı ya çok az ya da hiç yoktur. Bu durum fungusların geliĢmesine