1. Basically killing insects is not allowed while a person is in the state of Ihram except for when it is insidious and dangerous.
2. It is not permissible to use deodorants or fragrance nor is it permissible to smell such things. There is no problem in using insecticides or insect repellants for killing dangerous insects or animals but he should not smell them.
Indexes:
The answers given by religious authorities (grand jurists) to this question are as under:[1]
Grand Ayatollah Khamenei (may Allah grant him long life):
As an obligatory precaution, the person in the state of Ihram must avoid smelling any fragrant object even if it is not considered to be perfume.
Grand Ayatollah Makarem Shirazi (may Allah grant him long life):
The obligatory precaution is that the person in the state of Ihram should not kill insects such as flies, mosquitoes, ants and the likes irrespective of whether they are on his body or his clothe or elsewhere. In fact, the obligatory precaution is that he should not kill any living things except for when they are a cause of headache or are insidious and dangerous like snakes, scorpions and the likes. Even the obligatory precaution is that the said insects should not be thrown off the body and if he does so inadvertently, he must give some food to the poor.
Grand Ayatollah Sistani (may Allah grant him long life):
Basically killing insects is not allowed while a person is in the state of Ihram.
Ayatollah Hadavi Tehrani (may Allah grant him long life):
It is not permissible to use deodorants or fragrance nor is it permissible to smell such things whilst in the state of Ihram but if you use the insecticides to kill insidious insects and you do not smell them, there would be no problem.

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