Influence of pest control pressure on occurrence of ground beetles (Coleoptera: Carabidae) in apple orchards

Bioindicators that reflect the level of chemical control have not been developed for use in apple orchards in Japan. In Japan, many carabid beetles and spiders are beneficial predators of a wide range of agricultural pest insects. In apple orchards, spider numbers are reflective of the level of control pressure, but there is no information on carabid beetles. To establish whether carabid beetles could indeed be useful bioindicators, the number of carabid beetles and spiders in six apple orchards (A–F) under different levels of control pressure was investigated in Akita prefecture, northern Japan, in 2008 and 2009. The negative impact on beneficial arthropods was assumed to decrease in the order of pyrethroids (A) > organophosphates (B) > neonicotinoids (C) > insect growth regulators (D) > fungicides only (E) > no spraying (F). Sprays were applied at 2-week intervals from mid-May to early August. Twenty species of carabid beetles were found in orchard F; about 50% of adults were Anisodactylus punctatipennis, and 30–40% were Amara chalcites. The number of Am. chalcites significantly decreased with increasing control pressure: (A–C) < (E, F) in 2008, (A–E) < F in 2009, and (A, B) < E in 2009. Most spiders collected were juvenile Tetragnathidae and Araneidae. The numbers of spiders and Am. chalcites adults were significantly highly correlated at each control pressure in both years. Thus, it was considered that only Am. chalcites adults can be used as bioindicators reflecting the control pressure in apple orchards in northern Japan, whereas the main diet of this species is probably C3 plants.