Biology Reference
In-Depth Information
Wolbachia
, the fascinating intracellular bacterium that exerts cytoplasmic incompatibility and
other powerful effects, has also been found to inhabit cells of
Bactocera
spp.
(Kittayapong et al.,
2000). The promise of using
Wolbachia
spp. as biological control agents of agricultural pests has
been discussed (OÔNeill et al., 1997; Bourtzis and OÔNeill, 1998) and may include control of
tephritid pests. A comprehensive survey of pest tephritids for the presence of
Wolbachia
spp. and
other intracellular species has not been performed. Similarly, pathogens, such as microsporidia,
have not been vigorously sought after; however, they have been reported to cause disease in
tephritids, such as the Oriental fruit Þy,
Dacus
dorsalis
Hendel (Fujii and Tamashiro, 1972).
USE OF PROBIOTICS IN MASS-REARING PROGRAMS
AND STERILE INSECT TECHNIQUE
Contaminating microorganisms are a major problem at mass-rearing fruit Þy facilities. These
organisms have not been candidates for biological control agents because many of the microbial
species that cause disease in insects would also cause disease in humans and other animals. Measures
implemented to avert disease in insects also work to avoid contamination of diets and rearing
substrates by microorganisms that cause disease or decrease the nutritive and environmental con-
ditions of the substrates, i.e., pH, temperature, consistency, and viscosity. Antimicrobial agents are
often added to larval and adult diets; however, expense, issues concerning antimicrobial resistance,
and environmental-impact assessment of disposing diets containing these materials present real
obstacles for corrective measures.
Complete and accurate monitoring and assessment of the health of insect life stages and the
presence of microorganisms in rearing facilities is usually not done. This would accomplish many
goals. It would maintain consistent production, detect presence of pathogens before they reach a
level that would threaten quality assurance and control as well as output, decrease costs by using
corrective chemicals or treatment only when necessary, and allow use of corrective measures speciÝc
for the pathogen. The lack of information about disease in tephritids limits our ability to diagnose
and implement speciÝc and effective treatments. This direction would also provide information
about the production and use of acceptable pathogens for biological control.
A new applied aspect of tephritidÏbacteria research is the use of endosymbionts as probiotics.
Evidence is mounting that probiotic supplements play an important role in animal and human
nutrition and health, and thus it stands to reason that similar effects should apply to insects,
especially given the accounts of obligatory symbioses for certain insects. For example,
Sitophilus
oryzae
have been shown to be unable to Þy without their endosymbionts (Nardon and Grenier,
1991). Probiotics may hold much promise for improving the performance and Ýtness of mass-
reared insects, particularly tephritids. Probiotics have been shown to inhibit pathogens and alter
rates of apoptosis, a known effect of radiation exposure. Theoretically, probiotics would be added
to adult and larval diets, and the normal microbiota would rapidly establish as bioÝlms within these
stages. Normal metabolic and physical beneÝts would occur, radiation damage would be repaired,
and, as an extra beneÝt, the endosymbionts would competitively exclude contaminants that routinely
establish within the diets. Diet quality may be positively affected, and incidence of disease may
decrease. This is the hope, of course, behind the use of probiotics. Current studies are under way
to determine the true merits behind this idea, with preliminary data suggesting that probiotics may
indeed be a positive addition to mass-rearing protocols and lead to improvements in SIT (sterile
insect technique) effectiveness (Lauzon et al., 2000, unpublished).
CONCLUSIONS
Since the Ýrst accounts of tephritidÏbacteria associations, we have moved from the basic
observation of fruit Þy attraction, to proteinaceous compounds containing bacteria, to those of
