The effect of avocado ( Persea americana

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The effect of avocado (Persea americana) nectar composition on its attractiveness to honey bees (Apis mellifera)

Honey bees are important avocado pollinators, but due to low attractiveness of avocado flowers pollination is often inadequate. Since honey is of nectar origin, we used it to test the effect of nectar composition on the preference of honey bees and we identified avocado honey due to its perseitol concentration. Bees preferred feeders containing non-avocado honey to avocado honey even when total sugar concentration in the avocado honey was higher. Crop loads were smaller for bees feeding on avocado than non-avocado honey. Finally, the learning performance of bees in a proboscis extension conditioning experiment was lower when they were rewarded with avocado honey than with non-avocado honey or sucrose solution. Moreover, only for avocado honey did the percentage of bees refusing to consume reward increase during the experiment. Our results indicate that honey bees prefer honey whose floral origin is of a competing flora over that of avocado. We conclude that avocado nectar composition may contribute to the low attractiveness of avocado flowers

Inorganic nitrogen derived from foraging honey bees could have adaptive benefits for the plants they visit.

In most terrestrial ecosystems, nitrogen (N) is the most limiting nutrient for plant growth. Honey bees may help alleviate this limitation because their feces (frass) have high concentration of organic nitrogen that may decompose in soil and provide inorganic N to plants. However, information on soil N processes associated with bee frass is not available. The objectives of this work were to 1) estimate the amount of bee frass produced by a honey bee colony and 2) evaluate nitrogen mineralization and ammonia volatilization from bee frass when surface applied or incorporated into soil. Two cage studies were conducted to estimate the amount of frass produced by a 5000-bee colony, and three laboratory studies were carried out in which bee frass, surface-applied or incorporated into soil, was incubated at 25(o)C for 15 to 45 days. The average rate of bee frass production by a 5,000-bee colony was estimated at 2.27 to 2.69 g N month(-1). Nitrogen mineralization from bee frass during 30 days released 20% of the organic N when bee frass was surface applied and 34% when frass was incorporated into the soil. Volatilized NH3 corresponded to 1% or less of total N. The potential amount of inorganic N released to the soil by a typical colony of 20,000 bees foraging in an area similar to that of the experimental cages (3.24 m(2)) was estimated at 0.62 to 0.74 g N m(-2) month(-1) which may be significant at a community scale in terms of soil microbial activity and plant growth. Thus, the deposition of available N by foraging bees could have adaptive benefits for the plants they visit, a collateral benefit deriving from the primary activity of pollination

Cumulative respiration from three treatments in Study 2.

<p>The following treatments were incubated at 25°C for 45 days: 1) Soil+Water  =  soil (20 g) without bee frass; 2) Soil+Water+Frass  =  soil (20 g) with simulated rain (2 mL) before surface application of bee frass (20 mg); 3) Soil+Frass+Water  =  soil (20 g) with simulated rain (2 mL) after surface application of bee frass (20 mg). Bars are standard deviations.</p

pH, buffering capacity, total C, total N, and inorganic and organic N forms in soil and bee frass.

<p>ND  =  not determined.</p

Selected elemental composition of soil and bee frass.

<p>Selected elemental composition of soil and bee frass.</p

Nitrogen released (initial inorganic N + mineralized N), N mineralized, and NH₃ volatilized from bee frass in two surface-applied studies and one incorporated study held at 25°C for 15 to 45 days.

†<p>Within a column and study period, means followed by the same letter are not significantly different according to Fisher's protected.</p><p>LSD at p<0.05.</p>‡<p>Water+Frass(surface)  = 2 mL of water added to 20 g of soil, then 20 mg of frass applied on the surface.</p><p>Frass(surface)+Water  = 20 mg of frass applied on the surface of 20 g of soil, then 2 mL of water added to soil.</p><p>Frass (Incorporated)  = 20 mg frass incorporated into 20 g soil, then 2 mL of water added to soil.</p

Honey bee (Apis mellifera) strains differ in avocado (Persea americana) nectar foraging preference

Avocado nectar is unusual because it contains perseitol, a 7-carbon sugar alcohol. We compared avocado-nectar collection by commonly used Italian-based (IT) honey bee colonies and New World Carniolan (NWC) colonies introduced in avocado orchards in Israel (IS) and California (CA). In IS, NWC colonies had greater honey yields (1.2–4.3 fold), with a higher perseitol content (1.1–5.4 fold), than IT colonies. Overall, we calculated that NWC bees collected 1.4 to 18.1 times more avocado nectar than IT bees in the IS orchards. In CA, analyses of the crop contents of foragers revealed non-significant strain-specific trends in visitation to avocado flowers that were consistent with those indicated by data from IS. The genetic basis for honey bee differences in visitation to avocado flowers was further supported by the consistently high honey perseitol content of selected colonies over two years. The implications of possible strain-specific difference in avocado-nectar preference are discussed in relation to the use of honey bees for avocado pollination