You can use realtime-PCR (qPCR); extract total DNA from you insect samples (control+ treatments) then use a 16s universal primer in a realtime PCR.

You can use realtime-PCR (qPCR); extract total DNA from you insect samples (control+ treatments) then use a 16s universal primer in a realtime PCR.

I agree... real time PCR. Should you have a specific target bacteria, you can use specific primers and normalize it with the 16s quantification to get relative quantification of that specific bacterial DNA.

Thanks, and I wonder whether the 16s universal primer is used for amplifying bacterial 16S or insect?? 

Your answer is: for bacteria.

16s is abbreviated form for 16s Ribosomal RNA region (also called 16s-rDNA) inside prokaryotic genomes which is highly conserved and unique for each bacterial species and can use as standard DNA bar-coding among bacterial kingdom. with a simple search in google for "universal 16s primers" you can find some sequence for use

Thanks so much Reza, what your mean is that I use 16s as target gene for real-time PCR, and same amount of total DNA as templates from control and treatment. Is it right?  

first, you answer this: why do u want to measure a bacterial DNA level in single insect level? for that purpose? answer this, so i can tell you what can be your control and treatments

You can conduct quantitative PCR (qPCR) for this. Of course, you should be careful about the specific primers you use for that purpose.  

Thanks all guys.

Dear Yi Xu, 

find attached a nice paper from Paul and Linda Baumann (1994), dealing with your question. How to measure the number of bacteria in a single insect. This case is done with Buchnera aphidicola and its insect host, the aphid S. graminum. This work used qRT-PCR based on rrs or 16S rDNA and weighting of single insects at different developmental stadiums.

Aphids are the model insects for insect-bacteria interactions, so this paper will help you with your work. The primers used in this paper almost amplifies lots of bacteria but not all (primers are listed in Munson et al 1991, attached also), you can try the ones described in vanHam et al 1997 (also attached) that I used for locate primary and secondary symbionts in several insects from different genera and order. See also my paper with van Ham et al 2000, we used also these primers lots of time and worked really nice. 

Hope this helps you

Beatriz

I forget to mention that the DNA extraction method also affects the results in qRT-PCR. The paper from Baumann used phenol-Chloroform in-home solutions, but this protocol is out of date nowadays. You sould try several to find the optimal. I generally use the kits from Qiagen, are the best ones in my opinion, but are also expensive. When I don't have budget, I use homemade solutions like Salting-out protocol, which works really nice for routine insect DNA extractions! (check my papers if you like), and I llike it very much as is easy and non toxic as I don't use phenol:Chloroform nor other toxicals. 

hope this helps you,

Beatriz