Influence of Low Temperatures on Development of Preimaginal Stages of Colorado Potato Beetles
Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae)

• Hiiesaar, K., Metspalu, L., Jõudu, J., Jõgar, K.
• Institute of Agricultural and Environmental Sciences Estonian Agricultural University, 64 Kreutzwaldi St., 51014 Tartu, Estonia
• The Third International Conference onIPM Role in Integrated Crop management and Impacts on Environment and Agricultural Products. 26-29 November 2005, Giza, Egypt.

Abstract

In northern regions preimaginal stages of Colorado potato beetles (CPB) are not safe from unfavourable conditions like summer night frost or longer lasting temperatures below the development threshold over the entire vegetation period. The hatchability of eggs and survival of I and IV instar larvae after temporary exposure at low temperatures were studied. The egg clutches were exposed to five different temperature regimes, 7.0 ± 0.5°C, 3.0 ± 0.5C, -2.0 ± 0.5, -4.0 ± 0.5°C and -6.0 ± 0.5°C, and larvae to two different temperature regimes, 7.0°±0.5° C and -3.0°± 0.5 C for 24, 48, 72, 96, 120, 144 and 168 hours and after that they were transferred into the culturing conditions. There were no differences when eggs were exposed to the plus temperatures for up to 144-hr, they did not lose their ability to develop and hatch with the time. After 168-hr, larvae could not chew through the egg shell and perished. Cold damage increases with longer exposure to minus temperatures, and the lower the temperature, the quicker eggs became unable to develop: 144-hr exposure at -2 ± 0.5°C can be equalled to 72-hr exposure at -4 ± 0.5°C and 24-hr exposure at -6 ±0.5°C. CPB larvae could survive 144-hr exposure at low positive temperatures and first instar larvae were somewhat more resistant than those of forth instar. At a negative temperature -3 ± 0.5°C, after 96-hr exposure, the proportion of larvae able to survive and develop decreased rapidly and the limit of survival was 120-hr exposure, whereas 144-hs exposure killed all larvae. The tolerance of low temperatures of preimaginal stages of CPB is sufficient to enable their survival in the varying climatic conditions of northern regions, and thus they may develop constant populations there. But temporary low temperatures at the larval stage affect both the mass of beetles developed from these larvae and their offspring and it is he limiting factor of the increase in the number of CPB population in north regions.