Update this question was previously titled as \"Give me the name of a simple algorithm for signal(sound) pattern detection\"
You may be interested in a the MA Toolbox, a Matlab implementation of similarity measure(s).
I personally found this paper, General sound classification and similarity in MPEG-7, interesting. However, it might be behind a paywall (I don't know) and it might not be that useful in practice.
The GPL-ed framework Marsyas has a tool for machine learning classification, called kea. My guess is that this probably does not do what you want or is too much effort to hook up to.
My only idea otherwise is to take Fourier transforms, effectively transforming your sounds into grayscale images. Then use one of the many image similarity algorithms.
A step up from convolution is dynamic time warping which can be thought of as a convolution operator that stretches and shrinks one signal to optimally match another.
Perhaps a simpler approach would be to do an FFT of the sample and determine if your insect any particular frequencies that can be filtered on.
On the more complex side, but not quite a neural network, are SVM toolkits like libsvm and svmlight that you can throw your data at.
Regardless of the path you attempt, I would spend time exploring the nature of the sound your insect makes using tools like FFT. After all, it will be easier teaching a computer to classify the sound if you can do it yourself.
If I were you would start reading a little bit about Window Functions like Hamming window, this is a good starting point for sound recognition. (This is, of course, combined with Fourier Transformation)
A Naive Bayes Classifier may be worthwhile here, classifying sound samples into ones which contain your species of interest and ones which do not. It works quite well for complex phenomena; I once used it to decide if a given millimeter-wave RADAR data set contained an obstacle such as brush, a tank trap, etc. As for how to break up your continuous data into discrete chunks for the Bayesian classifier, you might just slide along the continuous data set and break off chunks equal in length to your insect sample. For example, if the sample you're comparing against is 2 seconds long, you might feed the discriminator 0-2s, 0.5-2.5s, 1-3s, etc. You'll need to train the discriminator, but that is a common requirement of any machine learning-based solution.
These sorts of approaches are about the only way to go if your insect species doesn't have a single, relatively distinct sound that you're looking for. Cross-correlation/convolution are of limited utility if you're looking for something more complex than a single sound which may be at higher or lower volume.
There are naive Bayes classifier implementations for several languages, such as nbc.
Goertzel - You can use it either for simple pattern detection, and for complicated frequencies separation. You can see the sample of my implementation in C#
Some more information is needed.
When you say noisy signal what is the background noise? Is it, to a first approximation, stationary (in a statistical sense, i.e. constant) or is it non-stationary (i.e. likely to contain other sounds, such as other animal calls etc?)
If the background noise is non-stationary then your best bet might be to use something called Independent Components Analysis which attempts to separate a given sound mixture into its component sources, you wouldn't even need the original recording of the insect itself. Lots of ICA software is linked from the Wikipedia page.
(Edit: ICA is a case of Blind Source Separation (BSS), there are many other ways of doing BSS and it might help to search for those as well.)
If however, the background noise is stationary then the problem is much easier (though still very hard):
In this case the approach I would use is as follows. Analyse the amplitude spectrum of a bit of the noise and the amplitude spectrum of your insect call. If you're lucky the insect call may, in general, be in a different frequency band to the noise. If so filter the incoming signal with suitable high-, low-, or band-pass filter.
You can then try comparing sections of your filtered signal that contain "more energy" than average with your (filtered) insect call. Possibly by using the image similarity algorithms suggested by A. Rex.
Edit: Since your background-noise is non-stationary then I can only suggest that searching for Blind Source Separation of non-Gaussian sources may lead you to some more algorithms. I'm afraid that the answer is that there is no simple algorithm that will do what you want.