Insecticidal control and the phenology of cherryslug (Caliroa cerasi (L.)) (Hymenoptera: Tenthredinidae) on organic pears in Central Otago

Cherryslug, Caliroa cerasi, is an important pest of organic pear production in New Zealand. It is reported to have two generations per year and cause severe leaf damage, particularly through the feeding of second generation larvae in mid to late-summer. This insect has been little studied in Central Otago. Adult cherryslugs were monitored with sticky traps in a block of ‘Taylor's Gold’ pears in the summers of 1999–2001 and the catches were used to assist in timing the single application each season of a range of organically-acceptable insecticides in randomized block experiments which included untreated control trees. The insecticides were: 1999–2000, ryanodine, lime sulphur, kaolin in January, kaolin in February; 2000–01, pyrethrum +mineral oil, lime sulphur, neem extract, kaolin in January. Efficacy was assessed using pre- and post-treatment larval counts and leaf damage. The impact of pre-treatment larval density on post-treatment efficacy was investigated to determine a preliminary spray threshold, sp...