HONEY BEES TO DISTRIBUTE BENEFICIAL BACTERIA TO APPLE AND ASIAN PEAR FLOWERS.

Fire blight, caused by Erwinia amylovora, is a bacterial disease which affects different commercial crops such as apple (Malus pumila) and Asian pear (Pyrus pyrifolia) also called nashi. Erwinia herbicola Eh252 is a biological control agent which inhibits the growth of E. amylovora on plate (Vanneste et al., 1992), and reduces the incidence of fire blight in field trials (Vanneste 1996). During the blooming period, flowers are the main point of entry for E. amylovora. The bacteria colonise the stigma, move to the nectaries and then enter the plant tissue (for a review see Vanneste 1995). Since limiting the incidence of fire blight is best achieved by preventing E. amylovora from entering the plant tissue, biological control agents are most efficient when brought directly to the stigma as soon as the flowers open, preventing E. amylovora from colonising these flowers.

Several laboratories have already shown that honey bees (Apis mellifera L.), placed in orchards to aid pollination, could be used to carry beneficial bacteria to apple flowers (Thomson et al., 1992, Johnson et al., 1993, Vanneste 1996). However, differences in flowering between host plants of E. amylovora could limit the use of honey bees as a vector of beneficial bacteria.
Nashi flowers, for example, open approximately 3 weeks earlier than apple flowers, when weather is not as warm, and when bees are not as active.
Honey bees also appear to be more attracted to apple flowers than nashi flowers.
In this study we determined whether honey bees could be used to disperse Eh252 onto nashi flowers, and we compared the efficacy of bees to carry beneficial bacteria onto nashi flowers to that obtained on apple flowers.

The trial on nashi was conducted in a commercial orchard in the Waikato (New Zealand), using 109 trees of the cultivar Kosui distributed in a 4300m² block of mixed varieties.
Two bee hives were placed in one corner of the block.
A pollen insert, a device which allows bees to pick up pollen or other materials before exiting the hive, was attached to each hive and 5 g of a lyophilised powder containing approximately 2.2 x 10¹¹ cfu/g of Eh252R, a spontaneous rifampicin resistant derivative of E. herbicol Eh 252, was placed into the insert at least once, and up to three times a day.
Powder was not loaded when the weather was not conducive to bee activity.
A total of 75 g of powder was used per hive over a 7 day period.
To determine the percentage of flowers colonised with Eh252R, two flowers (2–3 days old) were collected from each of the 109 nashi trees every day for seven days and individually washed in 10 mM MgSO₄. The pollen inserts were removed on the seventh day and the hive entrances cleaned of any visible Eh252R powder.
Flowers (2–3 days old) were collected from the 109 nashi trees four and eleven days later and checked for the presence of Eh252R as described above.
The percentage of nashi flowers colonised with Eh252R increased steadily to reach 81% on day 7 and 95% on day 18 (Figure 1).

The trial on apple was conducted in a commercial orchard in the Waikato using 184 Royal Gala trees (˜2 years old). One hive was placed in a corner of the block.
A pollen insert was attached to the bee hive and 5 g of lyophilised powder containing approximately 2.2 x 10¹¹ cfu/g of Eh252R were loaded into the insert up to four times a day.
A total of 50 g of lyophilised powder was loaded over a 3 day period.
To determine the percentage of flowers colonised with Eh252R, two flowers (2–3 days old) were

VIII International Workshop on Fire Blight

J.L. Vanneste, D.A. Cornish, M.D. Voyle, H.M. Haine, R.M. Goodwin

Fire blight, honeybees, biological control, nashi

https://doi.org/10.17660/ActaHortic.1999.489.107