Life Tables of the Apple Blossom Weevil Populations (Anthonomus pomorum L.) (Coleoptera, Curculionidae) on Apple and Pear Trees in Urbanized Territories of Moscow and Tver Provinces

Abstract

K-factor life tables and mortality factors of the apple blossom weevil Anthonomus pomorum (L.) (Coleoptera: Curculionidae) populations on apple and pear trees in three urbanized territories in Moscow and Tver provinces for three subsequent years are presented. The larva was the most affected stage. Among the biotic factors, the larvae and pupae were damaged by entomopathogenic microorganisms (presumably bacteria), the parasitoid wasps Pteromalus varians Spinola (= P. grandis Walker) (Pteromalidae), and predators, mainly thrips and sometimes pirate bugs of the genus Anthocoris. In 2016, the strongest effect of the biotic mortality factors on A. pomorum was observed on apple trees in the natural biocenosis of Dubki Park in Moscow, with the total residual mortality ΣK = 0.163; the weakest effect was observed on pear trees in a garden plot of Agronom horticultural partnership in Kimry District of Tver Province (ΣK = 0.079); the total residual mortality of the pest on apple trees in the test plot of the Laboratory of Plant Protection (Russian State Agrarian University – Moscow Timiryazev Agricultural Academy, Moscow) had an intermediate value of ΣK = 0.097. In 2018, the following mortality factors acting on A. pomorum population in Dubki Park were determined: diseases accounted for 2.8% of mortality (k = 0.012); predators, for 1.2% (k = 0.006); parasitoids, for 0.4% (k = 0.002); unknown factors (other than rains), for 18.5% (k = 0.093). In the test plot of the Laboratory of Plant Protection, the weevil mortality from the same factors was 1.35% (k = 0.006), 0.46% (k = 0.002), 0%, and 8.9% (k = 0.041), respectively. In 2017, rains were the dominant mortality factor for the III instar larvae. According to the life tables of A. pomorum on apple and pear trees in Moscow and Tver provinces, the survival of preimaginal stages sheltered inside the flower buds was very high, reaching 64–92%. An attempt was made to estimate the urbanization pressure using two main parameters derived from the life tables: the total population mortality during preimaginal development and mortality from parasitoids. In the growing season with the climatic conditions close to the long-term average, the effect of the urbanization factor on A. pomorum population could be assessed using the first parameter; however, in the season with abnormal weather conditions such assessment was found to be impractical, due to the varying effect of extraordinary precipitation levels on different weevil populations.