Impact of Lasius turcicus (Hymenoptera: Formicidae) on efficacy of vedalia beetle, Rodalia cardinalis (Coleoptera: Coccinellidae) in citrus orchards of Mazandaran province

Ants (Hymenoptera: Formicidae) can interfere with biological control of scale insects through protecting them against natural enemies. This study was carried out to investigate the impact of Lasius turcicus Santschi on feeding and functional response of vedalia beetle, Rodalia cardinalis on sour orange saplings in a citrus orchard in Sari County, northern Iran, during 2010. A 2-3-day old third instar (L3) or female beetle with a certain number of worker ants (including 0, 2, 4, 6, 8 or 10) were confined on a leaf which infested with a certain density of third nymphal instars of Icerya purchasi Maskell (including, 5, 10, 15, 20, 25, 30, 35, 40, 45 or 50). After 24 hours, the ant and ladybird were removed and the number of consumed scale was counted. The functional responses parameters were estimated using Rogers’ random predator equation. Results showed that the presence of ant on infested saplings decreased feeding of ladybird on scale. Mean daily feeding of females and third larval instars of ladybird decreased from 3.22 to 1.78 and 3.89 to 1.55 scales, respectively, while ant density increased from zero to 10 individuals per leaf. The functional response type was not affected by ant presence and a type II was observed in all treatments. In contrast, the values of functional response parameters were adversely affected by the ant activity. So that, by increasing ant density from zero to 10 individuals per leaf, the attack coefficient (a) of third larval instars of ladybird decreased from 0.143 to 0.009 and of adult females decreased from 0.0905 to 0.0002. After such increasing in ant density, handling times for third instars and adult females were increased from 6.84 to 10.79 and 7.36 to 10.04 hours, respectively. Because of adverse effects of this ant on feeding and functional response ofR. cardinalis, its presence on citrus trees should be considered in biological control and integrated pest management program of cottony cushion scale in citrus orchards of northern Iran.