Police monitored Baden-Clay's phone calls: court Police used "covert technology" to monitor the phone conversations of prestige real estate agent Gerard Baden-Clay after his wife Allison vanished, a court has heard. Homicide Detective Sergeant Peter Roddick told a Brisbane court on Tuesday he interviewed Mr Baden-Clay's mistress Toni McHugh on a number of occasions. Before Ms McHugh gave her fifth statement to police, he said, detectives issued her with a warning over her failure to disclose a phone call she had with Mr Baden-Clay. "She told us she had not had any contact with Gerard Baden-Clay and we were aware that that was not true," he said. Mr Baden-Clay's defence barrister Peter Davis asked how police came to be aware of the phone call. "I'm not really sure how to answer that ... covert technology," Detective Sergeant Roddick replied. Toni McHugh, Gerard Baden-Clay's mistress. He went on to deny ever instructing Mr Baden-Clay not to join the search for his missing wife in case he stumbled upon the crime scene. "It wasn't given to him by me and I'm not aware of that direction given to him per se," Detective Sergeant Roddick said. Detective Sergeant Gavin Pascoe, who was with the homicide squad at the time of Allison's disappearance, conceded it would be "fair to say" that Mr Baden-Clay became a person of interest very early in the police investigation. Mr Davis also asked him whether Mr Baden-Clay had been told not to participate in the search for his wife. "No, I don't recall that at all," the detective answered. Not to my knowledge ... but that's possible, yes. Earlier, the court heard from insect ecologist Professor Myron Zalucki, who was called upon by police to verify claims by Mr Baden-Clay that he suffered a bad reaction to a caterpillar. The court heard that the 42-year-old father of three told Taringa general practitioner Dr Renu Kumar on April 21 he had scratched himself after a caterpillar fell on him while he was in the garden. Professor Zalucki told the court he went to the scene where the "caterpillar incident" allegedly occurred. "Different people can have different reactions," he said. The court also heard on Tuesday from Dr Gordon Guymer, director of the Queensland Herbarium, who confirmed he found traces of six different plant species in samples taken from Mrs Baden-Clay's hair post-mortem. He found the same combination of six plant species at the Baden-Clay's Brookfield home - particularly around the car port - he said. Earlier the court heard from Christine Skrzeczynski, a teacher librarian, who claimed she was the woman seen by a witness walking in Brookfield on the morning Mrs Baden-Clay was reported missing.