Humberto Moo-Valle

The effect of food reserves on the production of sexual offspring in the stingless bee Melipona beecheii (Apidae, Meliponini)

Summary. A long-term study on the production of sexual offspring in relation to food stores was conducted in the stingless bee Melipona beecheii. Firstly, the production of sexuals was followed during one year in 10 colonies kept under natural conditions. Of the brood produced, 22.9% were males, and of all female brood, 14.6% were queens. Secondly, we measured the effect of experimentally manipulating the amount of food stores. One set of colonies started with 1.5 kg of food reserves and were regularly fed with pollen and nectar while another set were subjected to reduced food reserves of 0.5 kg, and were not given any extra food. Throughout the study, colonies with no treatment had brood and adults of both sexes all year round with no evidence of their presence being linked to swarming. Colonies with reduced food stores produced fewer males (0.7%) and queens (10.5%) than untreated colonies or colonies with enlarged food stores. The production of sexuals in colonies with enlarged food stores (23.4% males, 13.5% queens) did not differ significantly from that under natural conditions.¶We conclude that in Melipona only colonies that have accumulated large food stores produce sexuals that contribute to the reproductive population. This may lead to marked differences in the amount of sexuals produced by different colonies, although at the population level sexuals may be present all year round.

Comparative toxicity of pesticides to stingless bees (Hymenoptera: Apidae: Meliponini).

ABSTRACT Stingless bees are potential pollinators of commercial tropical crops and their use may increase in the short term. However, studies comparing the toxicity of pesticides to different individuals and species are lacking, making it difficult to evaluate their short- and long-term effects on colonies and populations of these insects. In this work, we tested the lethality of compounds from the main pesticide groups on stingless bees of the species Melipona beecheii Bennett, Trigona nigra Provancher, and Nannotrigona perilampoides Cresson. The LD50 (in micrograms per bee) for each pesticide was calculated for callow workers and foragers of the three species as well as for gynes and drones of M. beecheii. The results showed that all species were highly susceptible to the evaluated compounds. Nicotinoid pesticides were the most toxic, followed in descending order by permethrin, diazinon, and methomyl. We found evidence of a relationship between the body weight of the species and their LD50 for permethrin and methomyl (r = 0.91 and 0.90, respectively) but not for diazinon (r = -0.089). An analysis of contingency tables showed that within each species, callow workers had higher mortalities than foragers (P < 0.01). In M. beecheii at similar pesticide dose more males died compared with females [&khgr;2(0.01),1 = 10.16]. However, gynes were less resistant than workers [&khgr;2(0.01),1 = 8.11]. The potential negative consequences of pesticides to native stingless bees are discussed considering the reproductive biology of these insects. It is important to take actions to prevent damage to these key species for the ecology and agriculture of México and Latin America.

Pollination of ‘criollo’ avocados (Persea americana) and the behaviour of associated bees in subtropical Mexico

SUMMARY The flowering characteristics, contribution of self versus cross pollination and bee visitation were studied in ‘criollo’ avocado cultivars in Yucatán, Mexico. The pattern of pistillate and staminate stages (I and II, respectively), stigma receptiveness and the production of fruit in bagged and open panicles was followed in two commercial orchards. The number of bee visits across the day and the number of pollen grains on the body of workers of honey bees and two native stingless bee species were compared. Environmental variables were also recorded to determine their influence on bee visit rates. Few stigmas were morphologically receptive during the second day of opening of individual flowers (stage II). There was no overlapping between stages I and II. Open panicles produced significantly more fruit (60% on average) than bagged ones. Bee visits to flowers of both type A and B cultivars were significantly more frequent during the pistillate stage than during the staminate stage. Apis mellifera had an overall higher frequency of visits compared with the other two species. The number of pollen grains on the bees was not statistically different between A. mellifera (1644 ± 90.1 [s.d.]) and Trigona nigra (1356 ± 71.3) but it was significantly less in Nannotrigona perilampoides (781 ± 16.1). Environmental humidity had an influence on the visits of A. mellifera (r = −0.88) and N. perilampoides (r = 0.92) but not on T. nigra. It is concluded that self pollination is of limited influence in fruit production in avocado cultivars in subtropical Mexico and that both native stingless bees and honey bees potentially are efficient pollinators of this crop.

Pollination of habanero pepper (Capsicum chinense) and production in enclosures using the stingless bee Nannotrigona perilampoides

Summary A flower isolation experiment was conducted to determine the effect of self and cross pollination in habanero pepper (Capsicum chinense) in Yucatán, Mexico. The number of fruits increased, differing significantly (p<0.01) between bagged flowers (BF=25%), flowers that received one visit (V= 79%) and those with unrestricted visits (UV=86%). Likewise the numbers of seeds and the fertilization index differed significantly between treatments (p<0.01). In a second experiment, the efficiency of the stingless bee Nannotrigona perilampoides (SB) for pollinating this crop was evaluated. The quality of the fruit and the production in kg/m2 were not different between SB and mechanical vibration (MV) but the latter showed significantly lower values in the polar diameter, weight and number of seed per fruit (p<0.01). Both SB and MV showed significantly higher values compared with a test treatment where no pollinator was used in all the evaluated variables (p<0.01). We conclude that C. chinense can be self pollinated but cross pollination is needed to increase the number and quality of fruits and especially for high seed production probably due to the increased transference of pollen grains. The use of N. perilampoides seems a good alternative to the use of mechanical vibration and non native bees for pollination of peppers in enclosures under tropical conditions.

Patterns of intranidal temperature fluctuation for Melipona beecheii colonies in natural nesting cavities

SUMMARY Intranidal temperature fluctuation was studied in colonies of Melipona beecheii, an economically important stingless bee from Yucatan, Mexico. Two feral colonies nesting in tree cavities were used in the experiments. The brood and storage pots inside the nests were monitored for temperature changes using a telethermometer. Ambient temperatures immediately outside the logs were recorded simultaneously with ther- mohygrometers. Temperatures were recorded every hour for 24 h on four non—consecutive days. Differences between ambient temperatures and temperatures within nests were noted during the day and night. In all cases temperatures in brood and storage pots area were different from the ambient temperature (P < 0.01). There was no significant relationship between intranidal and ambient temperatures during the day (09.00 h to 20.00 h) on all days of measurement (P > 0.01). However, during lower ambient temperatures at night (21.00 h to 08.00 h) intranidal and ambient temperatures were significantly correlated (P < 0.01). These findings indicate that temperatures inside natural nesting colonies of M. beecheii remain relatively stable during the day, but tend to vary at night. Colony temperatures at night may lag from 5–6 h behind ambient temperatures. Active temperature control in nests of M. beecheii thus seems unlikely, and therefore the ability to ensure stable temperatures within the nest might be an important factor limiting the successful adaptation of this species to hive culture.

Comparative temperature tolerance in stingless bee species from tropical highlands and lowlands of Mexico and implications for their conservation (Hymenoptera: Apidae: Meliponini)

The objective of this study was to evaluate the temperature sensitivity of three stingless bee species, one from the tropical highland transition Neartic-Neotropical region (Melipona colimana) and two from the tropical lowland regions (Melipona beecheii and Scaptotrigona hellwegeri) of Mexico. The changes in thoracic temperature, behavior, and mortality rate of workers and pupae of the three species submitted to control high and low temperatures were assessed. Workers of highland M. colimana regurgitated water and fanned their wings when submitted to high temperatures, a behavior reported here for the first time in a stingless bee. M. colimana consumed syrup and increased its thoracic temperature in response to cold environment. Workers and pupae of M. colimana experienced lower mortality rates than M. beecheii and S. hellwegeri. The results of this study showed the tolerance of M. colimana to a wider temperature range, possibly as a response to extreme conditions in its native environment. The implications of thermal susceptibility differences for the conservation of highland and lowland stingless bees are discussed.

Sweat bees on hot chillies: provision of pollination services by native bees in traditional slash‐and‐burn agriculture in the Yucatán Peninsula of tropical Mexico

Summary Traditional tropical agriculture often entails a form of slash‐and‐burn land management that may adversely affect ecosystem services such as pollination, which are required for successful crop yields. The Yucatán Peninsula of Mexico has a >4000 year history of traditional slash‐and‐burn agriculture, termed ‘milpa’. Hot ‘Habanero’ chilli is a major pollinator‐dependent crop that nowadays is often grown in monoculture within the milpa system. We studied 37 local farmers’ chilli fields (sites) to evaluate the effects of landscape composition on bee communities. At 11 of these sites, we undertook experimental pollination treatments to quantify the pollination of chilli. We further explored the relationships between landscape composition, bee communities and pollination service provision to chilli. Bee species richness, particularly species of the family Apidae, was positively related to the amount of forest cover. Species diversity decreased with increasing proportion of crop land surrounding each sampling site. Sweat bees of the genus Lasioglossum were the most abundant bee taxon in chilli fields and, in contrast to other bee species, increased in abundance with the proportion of fallow land, gardens and pastures which are an integral part of the milpa system. There was an average pollination shortfall of 21% for chilli across all sites; yet the shortfall was unrelated to the proportion of land covered by crops. Rather, chilli pollination was positively related to the abundance of Lasioglossum bees, probably an important pollinator of chilli, as well indirectly to the proportion of fallow land, gardens and pastures that promote Lasioglossum abundance. Synthesis and applications. Current, low‐intensity traditional slash‐and‐burn (milpa) agriculture provides Lasioglossum spp. pollinators for successful chilli production; fallow land, gardens and pasture therefore need to be valued as important habitats for these and related ground‐nesting bee species. However, the negative impact of agriculture on total bee species diversity highlights how agricultural intensification is likely to reduce pollination services to crops, including chilli. Indeed, natural forest cover is vital in tropical Yucatán to maintain a rich assemblage of bee species and the provision of pollination services for diverse crops and wild flowers.

Nectar Minerals as Regulators of Flower Visitation in Stingless Bees and Nectar Hoarding Wasps

Various nectar components have a repellent effect on flower visitors, and their adaptive advantages for the plant are not well understood. Persea americana (avocado) is an example of a plant that secretes nectar with repellent components. It was demonstrated that the mineral constituents of this nectar, mainly potassium and phosphate, are concentrated enough to repel honey bees, Apis mellifera, a pollinator often used for commercial avocado pollination. Honey bees, however, are not the natural pollinator of P. americana, a plant native to Central America. In order to understand the role of nectar minerals in plant—pollinator relationships, it is important to focus on the plant’s interactions with its natural pollinators. Two species of stingless bees and one species of social wasp, all native to the Yucatan Peninsula, Mexico, part of the natural range of P. americana, were tested for their sensitivity to sugar solutions enriched with potassium and phosphate, and compared with the sensitivity of honey bees. In choice tests between control and mineral-enriched solutions, all three native species were indifferent for mineral concentrations lower than those naturally occurring in P. americana nectar. Repellence was expressed at concentrations near or exceeding natural concentrations. The threshold point at which native pollinators showed repellence to increasing levels of minerals was higher than that detected for honey bees. The results do not support the hypothesis that high mineral content is attractive for native Hymenopteran pollinators; nevertheless, nectar mineral composition may still have a role in regulating flower visitors through different levels of repellency.

Pollination services of Africanized honey bees and native Melipona beecheii to buzz‐pollinated annatto (Bixa orellana L.) in the neotropics

Africanized honey bees (AHBs) are the predominant flower visitors of many plants in the neotropics, although little evidence is available on their efficiency as pollinators on native crops. Annatto (Bixa orellana) is a buzz‐pollinated neotropical tree. We compared the pollination service provided by AHBs and native Melipona beecheii (Mb) to annatto in the Yucatan. As a result of the different abilities of both species to sonicate, a prediction of the present study is that AHBs on individual visits would result in less efficient pollinators on this crop. A higher frequency of AHBs on flowers (73.8%) compared with Mb (21.3%) was found. However, AHBs deposited significantly less pollen on the stigma and produced less fruits, with fewer seeds and weight, than Mb. A higher pollination index efficiency was obtained for Mb (0.9) compared with AHBs (0.6). AHBs did not sonicate annatto and gleaned the pollen released after Mb visits, which suggests that they act as commensals of the latter. By acting as commensals, AHBs, despite their high abundance, appear to marginally contribute to the pollination of annatto. Studies conducted under scenarios with a differential abundance of AHBs and efficient sonicating species are necessary to test this hypothesis on annatto and other buzz‐pollinated plants in the neotropics.

Does larval food affect cuticular profiles and recognition in eusocial bees? a test on Scaptotrigona gynes (Hymenoptera: Meliponini)

The relative contributions of heritable and environmentally acquired components of colony odor towards individual recognition are scarcely known in social insects. Larval food may affect cuticular profiles which in turn may serve as cues in the process of elimination of excess gynes characteristic of the eusocial stingless bees. In this study, we evaluated the contribution of larval food to cuticular profiles of stingless bee gynes and quantitatively tested if recognition (latency) from workers may be related to gyne chemotype and origin in the species Scaptotrigona pectoralis. Our results showed that the origin of food did not significantly affect the cuticular profiles of gynes, as larvae of the same origin reared on food from different colonies showed similar cuticular profiles at emergence. We suggest that overlapping over floral resources may account for the similarity in cuticular cues derived from food across experimental colonies. Additionally, workers showed similar latency time to first aggression towards gynes irrespectively of their chemotype and origin. Gyne’s mass had no effect on the aggressive response from workers either. We observed that gynes threatened aggressive workers which counteracted further aggression. Our results indicate that in stingless bees, cuticular hydrocarbons at emergence seem to have genetic origin and that gyne tolerance seems not related to cuticular chemical profiles. We suggest that cuticular cues may serve as caste labels for the identification of newly emerged gynes after which worker aggression towards them would elicit behavioral indicators of their fitness.Significance StatementWe studied the effect of larval food on the cuticular profile of stingless bee gynes coupled with an evaluation of the effect of chemotype in gyne recognition by workers in Scaptotrigona. We used artificial methods of gyne rearing that avoid nest odor acquisition of newly emerged individuals so that the effect of food could be better analyzed on gynes reared on food of their own colony and a different one. The origin of larval food did not significantly affect the cuticular profiles of gynes and workers attacked gynes irrespective of their chemotype. Our results demonstrate that cuticular chemical profiles are explained by genetic origin and not larval diet and that workers’ aggressive responses to gynes are independent of gyne colony origin.