Small sweat bees (Hymenoptera: Halictidae) as potential major pollinators of melon (Cucumis melo) in the Mediterranean

Abstract

In the current scenario of a general decline of the honeybee worldwide, studies on the potential of alternative bee species in pollinating cultivated plants are important. Although melon, Cucumis melo, is a crop with great commercial importance, there is very little information on its pollinating fauna in Europe, and none from the southern Mediterranean area. In a locality in central Spain, using both pan‐traps and net collections, we found that melon flowers are visited by 31 species of bees spanning four families, though only four were both dominant and constant. These four species belonged to the family Halictidae (sweat bees) and mostly (three species) to the genus Lasioglossum. Five other species could be defined as accessory: honeybee, Apis mellifera, and four other halictids. Individuals of the dominant species were smaller, on average, than those from all the other species. Observations on the frequency of pollen and nectar foraging and on flower visit duration further suggested L. malachurum as the potential key pollinator. Females of this species started to forage on melon early in the flowering season and exhibited two activity peaks in summer, thus covering the whole season. Although in other sites across continents melon seems to be more heavily pollinated by honeybees, this seems to be not the case in the Mediterranean, where sweat bees seem to be the major pollinators of this crop.

The Role of Annual Flowering Plant Strips on a Melon Crop in Central Spain. Influence on Pollinators and Crop

“…We have focused on this group because it was the most abundant in both the flower strip and the melon flowers, and because some small bees belonging to the family Halictidae (genus Lassioglossum spp.) have been previously identified as a key pollinators of the melon crop in Central Spain, such as the eusocial L. malachurum (Kirby, 1802) [52], which is also seen in our study. In 2013, the most visited plant for these bees was B. officinalis, which does not have a high pollen content and mainly supplies nectar [75]; therefore, this could have probably generated an increase in pollinator foraging activity, trying to seek pollen in nearby resources such as the melon crop.…”

“…Those visitors captured in the melon flowers were noted down. Species present in Central Spain were identified according to the Atlas of Hymenoptera [60] and Ortiz-Sánchez [61], and some of them were already well-known [32,52,55].…”

“…In recent decades, there have been many reports of unusually high rates and nectar; therefore, melon requires bee pollination to improve fruit quality and quantity [50,51], and farmers usually introduce 2-5 A. mellifera hives/ha. This crop is also visited around the world by a wide variety of other pollinators, mainly wild bee species [1,45,51,52], harbouring the Halictidae genus Lasioglossum in Central Spain, many important key pollinators [52].…”

The effect of transplanting date and covering on the growth and development of melon (Cucumis melo L.)

“…Melon is a plant pollinated by insects only. When the period of keeping melon plants under cover is extended, fruit yields may decline because pollinating insects have more difficulty gaining access to the flowers [26]. In the present study, the length of plant covering period did not affect yield levels, which is consistent with the findings by Santos et al [27] who reported that the length of melon plant covering period (18,21,24,27, and 30 days) did not significantly influence fruit yields.…”

Insights from measuring pollen deposition: quantifying the pre-eminence of bees as flower visitors and effective pollinators

“…Wild bees are also vital, and often better than Apis, as crop pollinators, with the importance of honeybees often over-emphasised in the past (see Breeze et al 2011;Garibaldi et al 2013). For example, halictid bees are important for melon (Rodrigo-Gomez et al 2016) and watermelon (Garantonakis et al 2016), bumblebees are important for blueberries (Button and Elle 2014) and several wild bees are better than managed honeybees at pollinating apples (Mallinger and Gratton 2015), although it is only a few relatively common solitary bee species that are crucial across crops in general (Kleijn et al 2015). Table 5 Heterospecific deposition by different groups of bees and non-bees for all plant species pooled, at each study site.…”