Traps ineffective with Porina

Press, Volume CXII, Issue 33052, 20 October 1972, Page 8

Traps ineffective with Porina

Light traps are not effective in controlling infestations of Porina moth (Wiseana cervinata). This is the conclusion reached in a two-year study by Mr D. G. Kelly under the supervision of Dr R. P. Pottinger at Lincoln College.

The study, prompted in part by the appearance of various light traps for sale to farmers for this purpose, was made by Mr Kelly for the degree of master of agricultural science. He graduated earlier this year. Mr Kelly, who comes from the Methven district, found that rather than attracting moths which emerged close to the trap and killing them before they laid their eggs, light traps tended to catch moths which had flown from relatively long distances. These moths, which had already laid hundreds of eggs, landed by the trap

and laid many more eggs before finally being caught. This caused a very high number of eggs to be laid around the trap. Hence, the appearance of many Porina caterpillars in this area could be expected. During the study, it was found that in Canterbury Porina moths flew in large numbers when the wind was westerly, just prior to the passage of a cold front. The female moths emerged from the ground at about 7.45 p.m. and were immediately mated by males which had emerged about a quarter of an hour earlier. Immediately they started

laying hundreds of eggs. Up until 9 p.m. some females and many males might be caught in a

nearby light trap. It was found that up until this time the majority of moths caught in a trap had emerged within 20 yards of it. In studies using marked moths, not one could be attracted to a light trap from more than 40 yards. However, after about 9 p.m. on a warm evening, many female moths, having completed some of their egg laying, flew to heights of 20ft or more, and travelled rapidly downwind for distances of up to several hundred yards. It was found that these moths ceased flying once over a light trap and plummetted to the ground nearby. Many of them were eventually "attracted into the trap, but in the period between landing ad being attracted into the trap, many more eggs were laid. Given suitable conditions for survival, these eggs would produce enough caterpillars to destroy the pasture around the trap. Thus, it was found that any light trap did not significantly reduce the number of Porina caterpillars in a paddock, but merely served to increase the numbers in the area surrounding the trap.