Bee pollination benefits for avocado crops
Extract from Bulletin 4298: Honeybee pollination
Avocado
Persea americana
Fruit production: USA -- averages 9 t/ha; potential increase calculated at 32 t/ha. Spain -- average production is 8 to 12 t/ha.
Western Australia: For tree spacing 8 m x 5 m:
- Year 3 - 0.25 t/ha
- Year 4 - 0.5 t/ha
- Year 5 - 2.5 t/ha
- Year 6 - 5 t/ha
- Year 7 - 10 t/ha
- Year 8 - 15 t/ha
- Year 9 - 20 t/ha
(McCarthy, A. (2001) Avocado culture in Western Australia, Bulletin 4484, Department of Agriculture)
Flowering:Late spring; late October to November in the South-west of Western Australia. Female flower sterility occurs at low daytime temperatures.
|
Avocado variety |
Type |
Flower period (Perth) |
Flower period (Carnarvon) |
| Anaheim | A | Sept - Oct | Sept - Oct |
| Bacon | B | Sept - early Nov | Mid August - Sept |
| Edranol | B | Sept - Oct | End August - Sept |
| Fuerte | B | Aug - Nov | End August - Sept |
| Hass | A | Late Sept - Nov | End August - Sept |
| Hazzard | A | Sept - Nov | End August - Sept |
| Hellen | B | Late Sept - Nov | End August - Sept |
| Linda | B | Mid Aug - Nov | Aug - Sept |
| Millicent | B | - | Aug - Sept |
| Nabal | B | Late Sept - Nov | End August - Sept |
| Reed | A | Late Sept - Nov | End August - Sept |
| Rincon | A | Aug - Sept | Mid Aug - Sept |
| Ryan | B | Mid Sept - Mid Nov | End Aug - Sept |
| Sharwil | B | Sept - Oct | Sept |
| Shepherd | B | Sept - Oct | End Aug - Sept |
| Talbot | A | Sept - Nov | End Aug - Sept |
| Taplin | B | Sept - Nov | Mid Aug-Mid Sept |
| Willard | A | Aug - Sept | End Aug - Sept |
| Wurtz | A | Late Sept - Oct | End Aug - Sept |
| Zutano | B | Sept - early Nov | Early Aug - Sept |
See also:'Avocado: further information on the biology of pollination'.
Hives per hectare:
50 to 75 per 10 ha; 5 to 8; 2 to 4 (Qld).
Honey production:
Dark.
Avocado: Review of bee pollination benefits
- Honey bees represented 81 per cent of insect visitors(South Africa) - see Abstract
- Avocado pollination by honey bees is mainly a process of direct pollen transfer; indirect pollination(where pollen transfer occurs in the hive) plays a limited role (Israel) - see Abstract
- Bees that collect only pollen usually do not visit female (pistillate)flowers and do not contribute to pollination (Israel) - see Abstract
- Significant initial fruit set required a density of at least 5 bees per tree during the female stage of flowering pollination (Israel) - see Abstract
- Avocado yield with and without honeybees - Australia: See tables below
- In an avocado orchard, honey bees tended to travel upwind and this tendency increased with increasing wind velocity. All bees travelled upwind in strong wind conditions. The percentage of cross-pollinating bees decreased with increasing distance from the pollen source. - see Abstract
- Further information on the complex interactions during insect pollination of avocado - see 'Avocado: further information on the biology of pollination'.
Avocado yield with and without honeybees - Australia
Avocado yield with and without honeybees. (Vithanage, V. (1989) Proc. 2nd Aust and Intnl Bee Congress, pp. 142-43)
|
Avocado |
Without hives |
With hives |
Statistical significance of difference |
| Mean fruit wt (g)/tree | 0.270 | 0.238 | ns |
| Mean no. of fruits/tree | 227.2 | 788.2 | P=0.05 |
Effect of increasing the number of hives/ha on the average fruit weight of avocado. (Vithanage, V. The role of pollination in improving yield and quality of fruits and nuts. Australian Postharvest Conference 1993)
Average fruit weight (kg)
|
2 hives per hectare |
3 hives per hectare |
Statistical significance of difference |
|
| Site 1 | 0.241 | 0.279 | P=0.05 |
| Site 2 | 0.247 | 0.297 | P=0.05 |
Avocado: further information on the biology of pollination
The insect pollination of avocado is a complex interaction, with research showing honey bees playing a leading role
- Stages of flowering in avocado
- Mechanisms of avocado pollen transfer
- Need for cross-pollination in avocado
- Placing hives in avocado orchards for pollination
- Summary of biology of avocado pollination
- Abstracts of scientific papers on avocado pollination
Stages of flowering in avocado
Each avocado flower goes through two stages of flowering.
| Pistillate - Stage I | The flower first opens as female. This is when pollination and fertilisation occurs. |
| Staminate - Stage II | Later, the same flower reopens as a male, when the anthers shed their pollen. |
To complicate matters even further, there are two 'types' of avocado.
| Type A | Cultivars such as Hass, Hayes and Reed | These cultivars have female flowers that open in the morning, then close completely, and reopen as male flowers in the afternoon of the following day. |
| Type B | Cultivars such as Fuerte, Sharwil and Zutano | These cultivars have female flowers that open in the afternoon, then close overnight and reopen in the male stage the following morning |
If this was not complicated enough, temperature can significantly alter these daily phases of Stages I and II. A one degree Celsius decrease in average daily temperature delays the flowering times by 20 to 60 minutes(see Abstract for further details). On cold days (less than 18 degrees C), the morning stages are delayed to the afternoon, and afternoon stages appear next morning. Don't forget cool weather (less than 13 degrees C) will also limit honeybee foraging activity.
Mechanisms of avocado pollen transfer
Pollen transfer occurs when Type A pollen is available to Type B female flowers in the afternoon, and vice versa. Many cultivars show sufficient overlap (a bisexual phase) in Stages I & II to allow self-fertilisation (see Abstract for further details).
This occurs more frequently in Type A plants (such as Hass) than Type B plants. In Hass X Hassorchards (intra-cultivar pollination), fruit drop is significantly higher than in say Hass X Ettinger orchards. A Hass X Hass orchard still benefits greatly from honey bee pollination, particularly in cooler climates where large shifts in average daily temperature cause large changes in daily flower rhythm.
Pollen can remain viable on the bodies of honey bees from Stage II flowers to Stage I flowers, especially for Type B trees because of its shorter (20 hour) flower cycle. Pollination may be lessened for Type A trees because pollen must be viable on honey bees up to 16 hours longer (Type A trees have a 36 hour flower cycle).
Research has shown that honey bees working the cultivar Hass have far less pollen distributed over their bodies than honey bees foraging on either Fuerte and Ettinger. Avocado pollen is mostly found on the bees legs, underside of thorax and abdomen and head after visiting staminate (stage II) flowers -- see Abstract for further details.
Need for cross-pollination in avocado
Research has shown that insect pollination is necessary -- when self-pollination within a tree is possible, caged trees (to exclude insects) rarely produce fruit ) -- see Abstract for further details. When Type A and B trees are caged together without insects, poor fruit yields are also obtained. Honey bees are therefore an important component of any avocado orchard production system.
A number of Western Australian growers have had production difficulties before they hired beehives. One grower has said "The day I brought in hives, I have never looked back".
Placing hives in avocado orchards for pollination
Traditionally, most orchards have used two hives per hectare. CSIRO research in New South Wales has shown that increasing hive numbers to 3 hives/ha (1.2 hives/acre) caused a corresponding and significant increase of 18 per cent in average fruit weight, from 244g to 288g (see Abstract for further details).
The number of fruits per tree also increased (625 to 684), but not significantly. Other research has examined fruit yield and weight differences when an orchard has not used honeybees, compared with an orchard that has used honeybees. Where honeybees have been used, the fruit yield increased by 350 per cent (227 to 788 fruits per tree). In this particular experiment the huge increased yield caused a corresponding decrease in average fruit weight (by 12 per cent).
The distance-from-hive-to-tree factor plays an important role in obtaining optimal yields of fruit. South African research indicates that honeybees will forage up to 300 m along rows of 4 year old avocado trees and only 200 m across rows. Again, this is important information for growers setting up orchards or replacing some trees with pollinisers to maximise yield.
As the trees get older, anecdotal evidence suggests that these distances will be reduced. Other research work on distance found no significant differences in yield when the distance to the hive was about 22 -- see Abstract for further details.. That is to say, placing hives not less than 22 metres apart would be heading in the right direction for maximising the pollination service growers pay for.
Summary of biology of avocado pollination
|
Avocado (Persea americana) |
Abstract available? |
|
| Daily period of flowering | 6 am to 8 pm | |
| Type A plant (Hass) flower cycle | 36 hours | |
| Type B plant (Fuerte) flower cycle | 20 hours | |
| Time of Hass (Stage I) and Fuerte (Stage II) flower overlap | 5.5 hours | |
| Time of Hass (Stage II) and Fuerte (Stage I) flower overlap | 1.5 to 3.5 hours | |
| Nectar production in flowers | high, from six nectaries | |
| Pollen | heavy and sticky | |
| Pollen grains found after pollination | 2 to 7 grains per stigma | |
| Average range of pollen load on honey bees | 1,575 to 4,090 grains per bee | |
| Average honey bee dispersal of pollen | 25,600 grains/h/bee | Yes |
| Duration of visit to flowers by nectar collecting bees | 2 to 10 seconds per flower | Yes |
| Duration of visit to flowers by pollen collecting bees | less than 1 second per flower | Yes |
| Mean number of honeybees per 100 flowers | 16 per 100 flowers | Yes |
| Best temperature range for fruit set | 20 to 25 degrees C | |
| Increase in honey bee activity after adding 2 hives/ha | 500 per cent | Yes |
| Honeybee activity (2 hives/ha) | 20.4 visits/h/sq m of canopy | Yes |
| Recorded fruit yield increase from using beehives (from no beehives) in Hass X Fuerte irrigated orchard | 350 per cent(227 to 788 fruits per tree) | Yes |
| Further fruit weight increase from increasing hives from 2 to 3 hives/ha | 18 per cent | Yes |
| Avocado flower can be unattractive to bees when other crops are flowering nearby | For example, citrus, grape or wild radish within 3 km of orchard | Yes |
| Optimum temperature for pollen germination | 25°C | Yes |
| Pollen viability | Improved by increased relative humidity (RH), that is, 11.4% germination of pollen of Fuerte at 40% RH; 50% germination of pollen of Fuerte at 100% RH | Yes |
| Relative humidity and pollen germination | Fuerte is more sensitive to humidity than Nabal, Ettinger, Bacon or Zutano | Yes |
Abstracts of scientific papers on avocado pollination
These abstracts are taken from the published papers.
- Possible routes of avocado tree pollination by honeybees
- The behaviour of honey bees visiting avocado flowers and their contribution to its pollination
- The natural occurrence of insect pollinators in an avocado orchard
- Pollination of avocados, mangoes and litchis
- Low attractiveness of avocado flowers to honeybees limits fruit set in Israel
- The role of the European honeybee in avocado pollination
- Mobility of honeybees foraging in avocado orchards
- Effect of pre-incubation humidity and temperature on the in vitro germination of avocado pollen
Possible routes of avocado tree pollination by honeybees
TITLE OF PAPER: Possible routes of avocado tree pollination by honeybees
ABSTRACT: The avocado (Persea americanaMill.), known as a typical cross-pollinatedspecies due to its synchronously protogynousflowering rhythm, has now been shown to in fact be both an efficient neighbour and cross-pollinated tree which exposes part of its flowers to inter-cultivar pollination only, while the remainders are exposed to both intra-cultivarand inter-cultivarpollination. Ten morphological stages were recognised during the flower's life span. The flowers change their stage individually and within a two hour period it is changed on the whole tree. Both the appearance and disappearance of each stage are synchronised among the cultivar's trees. In all the cultivars which were checked a bisexual flowering phase occurred daily. Significant linear correlation of flowering time with temperature was found; the occurrence of the flower stages was delayed by 21-60 minutes for a temperature drop of 1 degree C. The staminateand pistillateflowers are similar in structure, thus ensuring that the bee touches both pollen and stigmas in a similar manner. No discrimination between staminate and pistillate flowers has been observed during the flight of nectar collecting bees.
AUTHOR: Gad Ish-Am and Dan Eisikowitch
JOURNAL: Acta Horticulture 288, Sixth Pollination Symposium 1991
The behaviour of honey bees visiting avocado flowers and their contribution to its pollination
TITLE OF PAPER: The behaviour of honey bees (Apis mellifera) visiting avocado (Persea americana) flowers and their contribution to its pollination
ABSTRACT: Observations of honey bees (Apis mellifera) foraging behaviour on five cultivars of avocado (Persea americana) were carried out in 1982-1984 and 1990-1992 in Galilee, Israel. Examination of the morphology of avocado flowers showed that the pistillate and staminate flower stages have similar structure. Bees collecting nectar or nectar and pollen, visited both pistillate and staminate flowers, and due to the flower structure they were forced to touch both pistiland anthers. Only limited sites on a bee's body contacted the anthers, and these 'collection sites' also contacted the stigma, which occupied the same position as the anthers of the inner stamens. Most avocado pollen grains on bees visiting staminate flowers were clumped at the 'collection sites' and constituted the main pollen available for pollination. Some pollen grains randomly distributed over the entire bodies of bees visiting either pistillate or staminate flowers could have been acquired inside the hive, and did not play an important role in pollination. The observations suggest that pollination within a cultivar is accomplished during the overlapping phase of its pistillate and staminate flowering, during which bees collecting nectar and pollen move freely among neighbouring staminate and pistillate flowers. Pollination between cultivars of opposite flowering type is carried out by bees moving between them throughout the overlapping period of pistillate flowering of one cultivar and staminate flowering of the other. Bees which collect only pollen usually do not visit pistillate flowers and do not contribute to pollination.
AUTHOR: Gad Ish-Am and Dan Eisikowitch
JOURNAL: Journal of Apicultural Research 32(3/4): 175-186 (1993).
The natural occurrence of insect pollinators in an avocado orchard
TITLE OF PAPER: Preliminary report on the natural occurrence of insect pollinators in an avocado orchard
ABSTRACT: A survey of insect pollinators was carried out in an avocado orchard on the Westfalia Estate during a 3-day period in September 1992. Observations began at 8.00 am and continued until 4 pm. Many insects other than honeybees visited the avocado flowers, but most species were present in such low numbers that even if they pollinated the flowers their influence could be assumed to be negligible. Most of the insects simply robbed the flowers of nectar and carried very little or no pollen. The only insects that appeared to pollinate the flowers were the honeybees (Apis mellifera), the small carpenter bee (Allodape microsticta) and a calliphorid fly (Rhyncomya forcipata). Of these, only the honeybees were present in sufficiently high numbers to influence pollination.
AUTHOR: C.D. Eardley and M.W. Mansell
JOURNAL: Yearbook - South African Avocado Growers' Association (1993) 16 127-128.
Pollination of avocados, mangoes and litchis
TITLE OF PAPER: Pollination of avocados, mangoes and litchis
ABSTRACT: The first year's results from an ongoing study of insect pollination in avocado, mango and litchi orchards near Tzaneen in the Eastern Transvaal Lowveld (South Africa) are discussed. All insect visitors were identified, honey bee foraging activity was investigated and the effect of pollinators on fruit set was determined by bagging 400 inflorescences while leaving another 400 to be open-pollinated. In avocados, in which 81% of visits were made by honey bees, insect pollinators were important for increased fruit set (a total of 33 fruits were obtained from the 400 open-pollinated inflorescences, compared with only 2 from the bagged ones). In mangoes, fruit set was poor in both open-pollinated and bagged inflorescences, probably a result of using the first inflorescences which growers normally remove. Honey bees were observed collecting extra-floral nectar from the bases of mango panicles. In litchis, honey bees were the most abundant visitors and fruit set averaged 6/inflorescence in open-pollinated panicles, compared with 2/inflorescence in bagged panicles.
AUTHOR: A.P. DuToit
JOURNAL: Inligtingsbulletin - Instituut vir Tropiese en Subtropiese Gewasse (1994) No. 262, 7-8.
Low attractiveness of avocado flowers to honeybees limits fruit set in Israel
TITLE OF PAPER: Low attractiveness of avocado (Persea americana Mill.) flowers to honeybees (Apis mellifera L.) limits fruit set in Israel
ABSTRACT: Avocado in the Western Galilee region of Israel was found to be dependent on honeybees for fruit set. A significant initial fruit set required a density of at least five bees per tree during the female stage of flowering. The early-blooming avocado cultivars were visited by enough honeybees on fewer than one-third of their blooming days. Because they were visited mostly at the end of their blooming season, and due to rainy days, not more than 5% of their entire season's flowers were exposed to sufficient pollination to set fruit. The late-blooming cultivars however, were visited by many bees and exhibited high initial fruit set. The attractiveness to honeybees of various avocado cultivars and some other plant species, which were found to compete for pollination, was measured by the coefficient 'r' obtained from correlations between bee density and reward measures of these plants, over the course of a day or season. At the beginning of the blooming season, the avocado flowers competed for nectar-foraging bees mainly with flowers of Citrus spp, and for pollen foragers with Brassicaceae and Fabaceae, all of which were more attractive to the bees. Since pollination was carried out only by nectar-collecting bees, Citrus spp. flowers presented the main limiting factor for initial fruit set in avocado. However, toward the end of its blooming season, the avocado competed with Poaceae, Asteraceae and Apiaceae flowers, and its relative attractiveness increased.
AUTHOR: G. Ish-am and D. Eisikowitch
JOURNAL: Journal of Horticultural Science and Biotechnology 73: 2 (Mar 1998).
The role of the European honeybee in avocado pollination
TITLE OF PAPER: The role of the European honeybee (Apis mellifera L.) in avocado pollination
ABSTRACT: Pollination of avocado, Persea americana Mill. (Lauraceae) was investigated. A wide array of insects was involved in pollinating avocado in orchards, with the European honey bee, Apis mellifera L., playing a leading role. Introduction of beehives during flowering significantly improved fruit set. A density of two hives per ha was sufficient to improve the yield but three hives per ha significantly increased the mean fruit weight of experimental trees.
AUTHOR: V. Vithanage
JOURNAL: Journal of Horticultural Science (1990) 65(1) 81-86.
Mobility of honeybees foraging in avocado orchards
TITLE OF PAPER: Mobility of honey bees (Apidae, Apis mellifera L.) during foraging in avocado orchards.
ABSTRACT: The mobility of the honey bee (Apis mellifera L.) during foraging has a great influence on the effectiveness of the bees as cross-pollinators. In this work, honey bee mobility was measured in avocado orchards, between neighbouring trees and up to a distance 15 rows.
The average number of bees crossing between adjacent rows in a 10 minute period was linearly correlated to bee density, and the corresponding percentage increased with the increase in wind velocity, from 30% in a light wind (4 km/h) to up to 65% in a strong wind (45 km/h). The bees tended to travel upwind and this tendency increased with increasing wind velocity. Consequently, under strong-wind conditions, up to 100% of the bees travelled to the adjacent upwind row in a 10 minute period.
The percentage of cross-pollinating bees decreased with increasing distance from the pollen source, following a hyperbolic curve, and reached 1% to 2% of the bees at a distance of 10 to 15 rows.
AUTHORS: G Ish-am, and D Eisikowitch
JOURNAL: Apidologie 29(3): 209-219, (1998)
Effect of pre-incubation humidity and temperature on the in vitro germination of avocado pollen
TITLE OF PAPER: Effect of pre-incubation humidity and temperature treatment on the in vitro germination of avocado pollen grains
ABSTRACT: Optimum in vitro germination of pollen grain of the avocado cultivars Fuerte, Nabal, Ettinger, Bacon and Zutano occurred at 25°C. However, there were significant differences between cultivars in percentage germination and relative humidity (RH) requirements for optimum pollen grain growth. The most sensitive cultivar to relative humidity was Fuerte, in which the germination of pollen grain rose from 11.4%, at 40% RH, to about 50%, after one hour at 100% RH. The germination percentage of Nabal pollen grain was already high at 40% RH and was not increased by higher relative humidity.
Increased relative humidity also helped to sustain the viability of avocado pollen. At 30°C and 5% RH the pollen grain of Fuerte quickly lost its ability to germinate, at 40% RH for 1 hour, germination was reduced spectacularly compared to pollen kept in saturated with moisture environment where it was not affected the first 24 hours. The effects of temperature and relative humidity on fruit-set and yield of avocado are discussed.
AUTHORS: M Loupassaki, M Vasilakakis, I Androulakis
JOURNAL: Euphytica 94 (2): 247-251, (1997)
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