The Koran does not specify those virgins will be female.
Whilst there are numerous sources, including the Qur'an, which tell us believing males will be rewarded with virgins, many who are concerned about the authenticity of the 72 virgins concept are under the misconception that there is only one weak (da`if) reference to the exact number of houri given to them. These narrations are in fact found in many hadith collections with varying levels of authenticity, ranging from hasan (good) to sahih (authentic).
For example, in the Sunan Ibn Majah, one of the six major Hadith collections, it states in a hasan (good) narration that every male admitted into Paradise will be given eternal erections and wed to 72 wives, all with libidinous sex organs. Similarly in another hadith with multiple narrators that has been graded hasan (good), it states that the martyr (shahid) will be married to seventy-two of al-hoor al-'iyn.
In the Sunan al-Tirmidhi, another of the six major Hadith collections, it states that the smallest reward for the people of Heaven is an abode with seventy-two houri. Note that this is not a "weak Hadith that has no Sanad (chain of narrators)", as some have claimed. It has been graded hasan sahih gharib, meaning this hadith is hasan since it has several chains of transmitters, it is sahih as the chains are all authentic and it is gharib in the words that Imam Tirmidhi narrated.
Also reported in Sunan al-Kubra and Musnad Ahmad ibn Hanbal, and declared sahih (authentic) by Ibn Abi Shayba, Ibn Hibban, and al-Hakim is the hadith that states the servant in Paradise will be married with seventy wives and that they'll be given the sexual strength for a hundred.
Orthodox Muslim theologians have related further hadith that give us the exact number of 72, such as al-Ghazali who wrote, "[The Prophet said] the lowest rank of an inmate of Paradise will have eighty thousand servants and seventy two wives."
Suicide is clearly forbidden in Islam, but the permissibility of martyrdom operations (Istishhad) is an altogether different topic, with scholars being split on the issue.
Notable scholars and apologists such as Shaykh Yusuf Al-Qaradawi, the world's most quoted independent Islamic jurist, Dr. Zakir Naik, known for his advocacy of "Qur'anic science", and Tahir Ashrafi, the Chairman of the All Pakistan Ulema Council, have justified the use of suicide bombing in Islam. Opinion polls have further shown that an extremely large number of Muslims from around the world support the practice.
The Qur'an states that all Muslim males, not only martyrs, will be rewarded with virgins. However, the Qur'an does also mention that those who fight in the way of Allah (jihad) and get killed will be given a "great reward", and there are also hasan (good) hadith which refer to 72 virgins as one of the "seven blessings from Allah" to the martyr. This has lead to the 72 virgins concept being widely used as a way to entice other Muslims into carrying out "martyrdom operations" for Islam.
This is witnessed in Palestine, where the actions of a mother who sends her son to die as a martyr is sometimes seen as "marrying him off", and where the concept is used in Friday sermons and music videos, both airing on official television. It has even been used in the United Kingdom, where, in one event, Muslim teens were told to train with Kalashnikov rifles with the promise that the would receive 72 virgins in paradise if they died as religious martyrs.
Contrary to what the Qur'an, hadith, scholars and Muslims themselves say, a Western author named Margaret Nydell in a book that "promotes understanding between modern-day Arabs and Westerners", states that mainstream Muslims regard the belief of 72 virgins in the same way that mainstream Christians regard the belief that after death they will be issued with wings and a harp, and walk on clouds.
However, both the Qur'an and Muhammad in the hadith literature discuss the issue of virgins being provided for men in Paradise. So, unless the Bible, and more specifically Jesus in the four Gospels, claims Christians will indeed be issued with wings and a harp upon their arrival in Heaven, this claim is inaccurate and misleading.