It is difficult to say if the same is true for students in colleges and universities in the United States, but a recent survey in Britain found economics majors to be the most promiscuous.
I am sure we can all agree that the common description of economics majors as being “boring” or “too serious” is more urban legend than driven by data. According to the survey, economics majors report having 4.88 partners while the second most, social work, community care and counseling report 4.7 (see report of survey at http://www.dailymail.co.uk/news/article-2209275/Economics-students-promiscuous-campus.html?ITO=1490 ).
In my opinion, one of two factors could be driving these results. The first is that for the most part, undergraduate economics is taught primarily from a positive (what is or what will be) perspective as opposed to a normative (what should or ought to be) perspective. This could lead to students simply weighing costs and benefits of many sexual partners rather than incorporating societal norms. Another explanation is that since there is no truth telling constraint, economics majors choose to inflate their numbers.
Regardless of what is driving the results, this study reminds me of an argument that Steven Landsburg made many years ago ( http://www.slate.com/articles/arts/everyday_economics/1996/07/more_sex_is_safer_sex.single.html ). Landsburg made the argument that an increase in promiscuity could be better for society (read the article for the details). He also makes an argument for subsidizing condoms. This second argument brings me back to the study and has me hoping that if economists are the most promiscuous on campus, hopefully someone is subsidizing their condom consumption because most economists only consider private benefits and costs in the decision making process.