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Conservation biocontrol of pear psyllids

Mitteilungen Klosterneuburg


Anthocorid predatory bugs are known to be key natural enemies of pear psyllids but they often migrate into orchards too late and in too small numbers to effect timely and adequate natural regulation of pear psyllid populations. Tree and an herbaceous plant species for planting in hedgerows/windbreaks around pear orchards that are good sources of anthocorids early in the season have been identified. Preliminary work in 2008 indicated that goat and grey willow (Salix caprea and S. cinerea), hawthorn (Crataegus monogyna), nettle (Urtica dioica), ash (Fraxinus excelsior) and hazel (Corylus avellana) are promising sources of anthocorid predators. In 2009, established replicated plots of these were sampled on 8 occasions through the season to characterise predator communities, especially anthocorids, and their seasonal population dynamics and key prey and competing predator species present on them. A full data base of >70,000 specimens was collected and the most important insect groups were identified to species. Anthocoris nemoralis is the dominant anthocorid predator of pear psyllids. It is adapted to feed on psyllid eggs and nymphs. Anthocoris nemorum also occurs on pear, particularly later in the season. A. nemorum is adapted to feed on aphids. Psyllid larvae, on which A. nemoralis feeds, were found to be more numerous on trees very early in the season with egg laying and nymphs occurring from February onwards. Aphids become more numerous later in the season (May onwards) with a population crash or moving to a secondary host in July. Tree species that have psyllid nymphs early in the season (February to April) are most likely to support A. nemoralis early in the season and be good sources of these predators for pear psyllids. During the early season, the highest numbers of anthocorids were found on C. monogyna, S. caprea, S. cinerea and U. dioica. Tree species that support aphids provide large numbers of A. nemorum later in the season. The highest numbers of aphids were found on birch (Betula pubescens), C. avellana and U. dioica, though the aphids on B. pubescens did not appear to be preyed on by anthocorids. U. dioica is host to the nettle psyllid Trioza urticae which is abundant throughout the year in the adult stage. U. dioica is thus a good source of A. nemoralis early in the season. The nettle aphid Microlophium carnosum is also abundant when growth commences in spring, providing food for A. nemorum which is abundant later in the season. Thus U. dioica appears to be an excellent source of anthocorids, although it may also be a source of the common green capsid, Lygocoris pabulinus, a damaging though easily controlled pest of pear. It is concluded that hedgerows/windbreaks rich in S. caprea, S. cinerea and C. avellana with an abundant understory of U. dioica are likely to be excellent for conservation biocontrol of pear psyllids. C. monogyna was also found to be potentially excellent, but could be a source of fireblight if not carefully managed. Italian alder (Alnus cordata) windbreaks commonly provided round pear orchards provide little or no benefit for conservation biocontrol of pear psyllids. Mark and capture studies to investigate the migration of anthocorids from these conservation biocontrol subjects are in progress.

Author(s): Cross, J; Nagy, C; Batki, M; Linka, J

Journal: Mitteilungen Klosterneuburg

Year: 2010