EUROPEAN JOURNAL OF ENTOMOLOGY

Eur. J. Entomol. 103 (3): 547-551, 2006 | DOI: 10.14411/eje.2006.074

Effects of low temperatures on Chilocorus kuwanae (Coleoptera: Coccinellidae) trophic activity

Carlo RICCI¹, Andrea PRIMAVERA¹, Valeria NEGRI²

¹ Department of Agricultural and Environmental Sciences, Perugia University, Borgo XX Giugno, 06100 Perugia, Italy; e-mail: cricci@unipg.it

² Department of Biology and Agro-environmental Biotechnology, Perugia University, Borgo XX Giugno, 06100 Perugia, Italy

Chilocorus kuwanae Silvestri is an effective predator of Unaspis euonymi (Comstock), a scale insect harmful to spindle trees (Euonymus europeus L. and E. japonicus Thumb). The feeding behaviour was studied on wild adults, collected from spindle trees in the Botanic Garden of Perugia University, and fed on overwintering U. euonymi females. The insects were exposed to gradually changing constant temperatures (13°-->10°-->8°-->6°-->4°-->2°-->13°-->15°C) for a ten day period at each temperature. C. kuwanae adults preyed on the scale also at low temperatures. The number of scales eaten decreased with decreasing temperatures from the initial 13°C to 4°C, and at 2°C the trophic activity of C. kuwanae adults almost stopped although they made brief walks in the petri dishes. At all tested temperatures the ladybirds made holes in or lifted the scale cover and preyed on the female. Sometimes they lifted the scale cover , but did not prey on these U. euonymi females which were destined to die from cold. As the temperature dropped from 13°C to 4°C, the number of females eaten by ladybird males and females did not differ statistically. When the temperature was raised to 13°C and 15°C, the ladybirds resumed feeding. Large differences were recorded between sexes, with females showing a much higher feeding activity than males. Scale cover lifting was most frequent at the beginning of the experiment and then decreased with diminishing temperatures, although no significant difference was recorded among temperatures within the range from 10°C to 4°C. The threshold for trophic activity can be taken as 2°C since we noted that a few (12%) individuals on one day showed predatory activity. At 13°C and 15°C lifting activity rose again but remained at a lower level than at the initial exposure to 13°C. There was no significant difference in activity at 13 and 15°C upon raising the temperature. As for total number of U. euonymi damaged by C. kuwanae the trend in damage revealed the same pattern as for number of scales eaten. At the final exposure to 15°C, 60% of C. kuwanae females laid eggs. Our data demonstrate that C. kuwanae can reduce U. euonymi populations in a submediterranean environment even in winter when the range of temperatures is similar to that tested in this experiment.

Keywords: Coccinellidae, Chilocorus kuwanae, Unaspis euonymi, coccidophagous predator, low temperatures, Euonymus japonicus, Diaspididae, feeding behaviour

Received: December 8, 2005; Revised: February 6, 2006; Accepted: February 6, 2006; Published: July 3, 2006  Show citation