Effects of protein-constrained brood food on honey bee (<Emphasis Type="Italic">Apis mellifera</Emphasis> L.) pollen foraging and colony growth

Pollen is the sole source of protein for honey bees, most importantly used to rear young. Honey bees are adept at regulating pollen stores in the colonies based on the needs of the colony. Mechanisms for regulation of pollen foraging in honey bee are complex and remain controversial. In this study, we used a novel approach to test the two competing hypothesis of pollen foraging regulation. We manipulated nurse bee biosynthesis of brood food using a protease inhibitor that interferes with midgut protein digestion, significantly decreasing the amount of protein extractable from hypopharyngeal glands. Experimental colonies were given equal amounts of protease inhibitor-treated and untreated pollen. Colonies receiving protease inhibitor treatment had significantly lower hypopharyngeal gland protein content than controls. There was no significant difference in the ratio of pollen to nonpollen foragers between the treatments. Pollen load weights were also not significantly different between treatments. Our results supported the pollen foraging effort predictions generated from the direct independent effects of pollen on the regulation of pollen foraging and did not support the prediction that nurse bees regulate pollen foraging through amount of hypopharyngeal gland protein biosynthesis.     

Cuticular volatiles,attractivity of worker larvae and invasion of brood cells by Varroa mites. A comparison of Africanized and European honey bees

Summary. Africanized honey bees (AHBs) of Brazil and Mexico have proven to be tolerant to Varroa destructor mites. In contrast, European honey bees (EHBs: Apis mellifera carnica) at the same tropical study site are highly intolerant to these ectoparasites. A lower attractiveness of Varroa-tolerant AHB larvae has been hypothesised to be an important trait in reducing the susceptibitlity of AHBs to these mites. Thus, selection for EHB brood that is less attractive to mites is thought to be one possibility for limiting mite population growth and thus increase the tolerance of EHBs to the mite.?In Ribeir?o Preto, Brazil, European A. m. carnica bees and AHBs were tested with respect to their rate of brood infestation and brood attractiveness to Varroa mites. For the comparison of brood infestation rates, we introduced combs with pieces of EHB and AHB brood into honey bee colonies (18 repetitions). The relative infestation rate of EHB brood was significantly higher compared to AHB brood.?The preference behaviour of single Varroa mites was tested in a laboratory bioassay where either living host stages were offered or host extracts were presented on dummies. By these tests we could confirm the preference of Varroa females for certain developmental host stages and for their corresponding extracts. In contrast to the within-colony results, Varroa mites in the laboratory bioassay showed a slight preference for AHB compared to EHB larvae.?The gas chromatographic analysis revealed differences in the chemical spectrum of extracts obtained from different larvae. In accord with the results of the bioassays, we could detect stage-specific odour differences in larval cuticular compounds, including methyl esters and hydrocarbons that have been described as kairomones. None of these substances, however, revealed significant race-specific differences. Therefore, the quantity and composition of certain cuticular compounds seem to be responsible only for the recognition of a suitable host stage by Varroa females. The different infestation rates in the colonies, however, seem to be caused neither by race-specific differences in attractiveness of bee larvae nor by an extended attractive period of EHB larvae: both AHB and EHB larvae become attractive approximately 21 h before capping of the brood cell, and thus have the same window of time when they can be parasitised.?Therefore differential Varroa-infestation rates are not related to larval attraction but probably are determined by other race-specific and colony-related factors. Received 11 June 2001; accepted 19 November 2001.     

Task specialization in a wild bee,Apis florea (Hymenoptera: Apidae), revealed by RFLP banding

Workers in a wild in situ colony of the dwarf honey bee, Apis florea, were observed undertaking the following behavior: liquid foraging, pollen foraging, guarding, stinging, fanning and wagging abdomen. Bees of each behavioral class were separately collected and frozen. Collections were made over a period of 10 days. Random samples of brood and workers were also collected. DNA was extracted from each bee and fingerprinted using a probe of unknown sequence obtained from an A. mellifera genomic library. Patterns of fingerprints (Fig. 1) were dissimilar among behavioral classes (Tables 1 and 2), strongly suggesting a genetic component to division of labor in this species. This result supports similar findings in A. mellifera in a species that is not troubled by many of the experimental difficulties inherent in A. mellifera. Correspondence to: B.P. Oldroyd     

Impacts of flight distance on sex ratio and resource allocation to offspring in the leafcutter bee, Megachile rotundata

Fisher's theoretical prediction of equal investment in each sex for a panmictic population (The genetical theory of natural selection. Clarendon, Oxford, 1930) can be altered by a number of factors. For example, the sex ratio theory predicts variation in equal investment in each sex when the maternal fitness gains from increased investment differ between sexes. Changing sex allocation because of changing payoffs may result from different ecological situations, such as foraging conditions. We investigated the impact of foraging travel cost on relative investment in sons vs daughters. Field studies were carried out with the central-place-foraging leafcutter bee Megachile rotundata (Fabricius), which has smaller males than females. Therefore, less investment is required to produce a viable son compared with a daughter. We found that with increased flight distance to resources, females produced a greater proportion of sons. Females also invested fewer resources in individual sons and daughters and produced fewer offspring with increased flight distance.     

Directional change in a suite of foraging behaviors in tropical and temperate evolved honey bees (<Emphasis Type="Italic">Apis mellifera</Emphasis> L.)

The concept of a suite of foraging behaviors was introduced as a set of traits showing associative directional change as a characterization of adaptive evolution. I report how naturally selected differential sucrose response thresholds directionally affected a suite of honey bee foraging behaviors. Africanized and European honey bees were tested for their proboscis extension response thresholds to ascending sucrose concentrations, reared in common European colonies and, captured returning from their earliest observed foraging flight. Race constrained sucrose response threshold such that Africanized bees had significantly lower sucrose response thresholds. A Cox proportional hazards regression model of honey bee race and sucrose response threshold indicated that Africanized bees were 29% (P<0.01) more at risk to forage over the 30-day experimental period. Sucrose response threshold organized age of first foraging such that each unit decrease in sucrose response threshold increased risk to forage by 14.3% (P<0.0001). Africanized bees were more likely to return as pollen and water foragers than European foragers. Africanized foragers returned with nectar that was significantly less concentrated than European foragers. A comparative analysis of artificial and naturally selected populations with differential sucrose response thresholds and the common suite of directional change in foraging behaviors is discussed. A suite of foraging behaviors changed with a change in sucrose response threshold that appeared as a product of functional ecological adaptation.Communicated by R.F.A. Moritz     

Color choices by bumble bees (Bombus terrestris): innate preferences and generalization after learning

It is usually assumed that the choice behavior of bees for floral colors is influenced by innate preferences only for the first flower visits prior to any experience. After visits to rewarding flowers bees learn to associate their colors with a reward. This learning process leads to an acquired preference for the trained colors that has been believed to dominate over previous experiences and over innate preferences. This work investigates how bumble bees (Bombus terrestris) chose among artificial flowers of different colors after they had been extensively trained to other colors. The bees chose novel colors according to their similarity to the trained color if the trained color was similar to some of the test colors. This was true also if trained colors and test colors were well distinguished, so their color choice reflected generalization between colors. If the test colors were so different from the trained color that no generalization took place, choice behavior was not affected by the trained color and reflected innate preferences. The differences in choice frequencies could not be explained by physical properties of the test colors other than the dominant wavelength, a parameter taken to reflect hue perception. Preferred dominant wavelengths correspond to those observed in naive bumble bees and honeybees. Thus bumble bees show innate preferences for certain colors not only prior to color learning but also after intensive learning when choosing among very different novel colors. Color choice among similar colors, however, is controlled by generalization from the learned color. Received: 9 November 1999 / Received in revised form: 19 March 2000 / Accepted: 31 March 2000     

Pollen foraging: learning a complex motor skill by bumblebees (<Emphasis Type="Italic">Bombus terrestris</Emphasis>)

To investigate how bumblebees (Bombus terrestris) learn the complex motor skills involved in pollen foraging, we observed naïve workers foraging on arrays of nectarless poppy flowers (Papaver rhoeas) in a greenhouse. Foraging skills were quantified by measuring the pollen load collected during each foraging bout and relating this to the number of flowers visited and bout duration on two consecutive days. The pollen standing crop (PSC) in each flower decreased drastically from 0530 to 0900 hours. Therefore, we related foraging performance to the changing levels of pollen available (per flower) and found that collection rate increased over the course of four consecutive foraging bouts (comprising between 277 and 354 individual flower visits), suggesting that learning to forage for pollen represents a substantial time investment for individual foragers. The pollen collection rate and size of pollen loads collected at the start of day 2 were markedly lower than at the end of day 1, suggesting that components of pollen foraging behaviour could be subject to imperfect overnight retention. Our results suggest that learning the necessary motor skills to collect pollen effectively from morphologically simple flowers takes three times as many visits as learning how to handle the most morphologically complex flowers to extract nectar, potentially explaining why bees are more specialised in their choice of pollen flowers.     

Determination of Acaricide Residues in Saudi Arabian Honey and Beeswax Using Solid Phase Extraction and Gas Chromatography

Determination of acaricide residues of flumethrin, tau-fluvalinate, coumaphos, and amitraz in honey and beeswax was carried out using a rapid extraction method utilizing C-18 SPE cartridges and an analytical method utilizing GC with ECD, NPD, and MSD detectors for the four acaricides. Recovery percentages from the extraction method ranged from 90–102%, while the minimum detection levels ranged from 0.01–0.05 mg/kg for the acaricides. Nine of the 21 analyzed samples were found to be contaminated with the acaricides tau-fluvalinate and coumaphos. Neither flumethrin nor amitraz was detected in any of the honey or wax samples. Coumaphos was found only in honey samples in which two samples exceeded the tolerance levels set by EPA and EC regulations. It has not been detected in beeswax. Five honey samples and eight beeswax samples were found to be contaminated with tau-fluvalinate. One of the wax samples was contaminated with a relatively high residue of tau-fluvalinate and contained above 10 mg/kg.     

Solid-phase extraction for multi-residue analysis of pesticides in honey

A fast and simple multi-residue method for the analysis of 15 organophosphorus (OP), 17 organochlorine (OC), 8 pyrethroids (PYR), 12 N-methyl-carbamate (NMC) pesticide residues and bromopropylate in honey is presented. Ready–to–use EXtrelut®NT 20 column, eluted with dichloromethane, was used to extract the pesticide residues from the aqueous-acetone honey sample, obtaining a clean extract directly analyzable. Determination was carried out by gas chromatography (GC) coupled with flame photometric detector (FPD) for OP compounds and by GC coupled with mass spectrometry detector (MSD) for OC and PYR pesticides and bromopropylate. The NMC pesticides were analysed by liquid chromatography-double derivatization coupled with spectrofluorimetric detector (LC/DD/Fl). This method allows the determination of the 53 pesticide residues at low concentrations (0.0005–0.074 mg/kg) and can be used to assess the compliance with the Maximum Residues Levels (MRLs) set by the European Union. The performance of the method was evaluated and specificity, linearity, recovery, repeatability, reproducibility, limit of quantification (LOQ) and limit of detection (LOD) were determined. A good linearity (r²? 0.99) was found in the range 0.0005–0.074 mg/kg for the majority of the compounds studied. Most of the pesticides had recoveries in the range 70–103 % and values of relative standard deviation (RSD) < 20 for repeatability and reproducibility, showing good accuracy and precision of the method. Aldicarb partially degraded in aldicarb sulphoxide during the analytical procedure, giving anomalous values. The LOQ for all pesticides investigated was from 0.0005 to 0.025 mg/kg while the LOD ranged from 0.0002 to 0.008 mg/kg.