Sex pheromone attractants to improve the trapping and monitoring of mammal pests at low densities
Increasingly, now and in the future, mammalian pests will be controlled at low densities, such as after successful broad-scale control or a pest reinvasion of an island. In such situations, where the food supply is plentiful, there is likely to be a role for non-food-based lures to increase the efficiency of trapping and monitoring operations. Many of New Zealand’s major pests, such as stoats and possums, are solitary animals and seldom interact with their conspecifics. However, the one exception to this is during the mating period. Both possums and stoats are highly effective at finding mates using sex pheromone cues even at low densities, despite the period of oestrus (when the female is receptive) generally lasting only a few days and ending once mating has occurred.
A successful example of the use of non-food-based lures was the trapping of stoats after they recently reinvaded Kapiti Island. A stoat was seen on the Island in November 2010 and its presence confirmed by DNA analysis of scats located by trained predator dogs. The area was intensively trapped using traditional food-based lures for 3 months without success. Landcare Research supplied the Department of Conservation team on Kapiti Island with stoat bedding material in early February 2011 and within 10 days a male stoat was captured. By chance, the bedding material was collected from captive female stoats that were in oestrus and this may have been an important factor in the ability of the bedding material to be an effective lure. Scent lures containing odours or secretions from male or female possums, ferrets and stoats have been shown to be attractive to both sexes of their species, but no one has looked at the effect of reproductive state on attractiveness of such secretions.
Janine Duckworth has been investigating whether sex pheromone lures increase the encounter and interaction rates of possums and stoats with traps or monitoring devices. Janine’s team collected urine from captive female possums at the height of oestrus (24 to 72 hours before mating), as well as from non-breeding females and males. These samples were presented to penned possums by applying 0.05 ml of the urine on a gauze pad inside a plastic perforated lure station to determine how often and how long male and female possums spent investigating the urine-based lures and a saline control preparation.
Male or female possums didn’t usually interfere with (‘paw” or touch) a lure station when no pheromone-based lure was present. For both male and female possums, the number of interferences and the time spent interacting with preparations from non-breeding and oestrous females was significantly greater than for the control lure (Figs 1 & 2). Neither sex displayed any interest in male urine but there was no indication of avoidance either. Both male and female possums responded to the different lures in the same way. Female-derived preparations showed the greatest promise.
To test the ability of the possum secretions to increase trapping efficiency under field conditions when compared to the standard National Pest Control Agencies flour blaze, the oestrous female lure is currently being assessed in field trials (under contract to the Animal Health Board) using possums collared with radio-frequency identification tags (Using radio frequency identification technology to measure possum interaction rates with traps). Early results look promising.
In the longer term, sourcing sufficient biologically-derived active ingredients (bedding materials, urine or anal gland secretions) would limit the practicality of such lures for widespread pest control. Gas chromatography is therefore currently being used to identify differences in the profiles of volatile components present in the lure preparations from breeding and non-breeding females and from males. This will allow synthetic versions of the sex pheromone compounds to be developed and then tested for their ability to attract possums. New potent and potentially species-specific lures may be key to improving encounter and interaction rates with traps and monitoring devices for better, more effective pest control in the future and to make the goal of a ‘predator-free New Zealand’ more attainable.
This work was funded by Landcare Research Capability funding and field trials done under contract to the Animal Health Board.