Species and abundance of ladybirds (Coleoptera: Coccinellidae) on citrus orchards in Northland, New Zealand, and a comparison of visual and manual methods of assessment

Abstract

Ladybird populations were assessed on citrus orchards in Northland, New Zealand, from January 1991 to February 1994. Ten-minute visual counts were made during all months and compared with manual searches of trees on three occasions. Halmus chalybeus (steelblue ladybird) comprised 97-99% of the ladybirds found by both types of assessment and was present throughout the year. Over 95% of the ladybirds recorded in visual counts were adults, whose numbers peaked in February-March. The most larvae and pupae were recorded in December-January.A manual search for ladybirds at an orchard near Kerikeri, Northland, in November 1991 recorded 153 ladybirds/tree with 91% comprising egg batches, larvae and pupae. Searches at a nearby orchard in December 1992 found 22 ladybirds/tree (71% immature) and 59/tree in February 1993 (5% immature). Visual counts of ladybirds recorded approximately 4-5% of the number of adult ladybirds found by manual searches, but only 0-3% of egg batches, larvae and pupae.Visual counting was a suitable method for estimating numbers of adult ladybirds on citrus orchards, but not immature stages.