Stephen J. Stringer

Nectar Robbery by Bees Xylocopa virginica and Apis mellifera Contributes to the Pollination of Rabbiteye Blueberry

Abstract Honey bees, Apis mellifera L., probe for nectar from robbery slits previously made by male carpenter bees, Xylocopa virginica (L.), at the flowers of rabbiteye blueberry, Vaccinium ashei Reade. This relationship between primary nectar robbers (carpenter bees) and secondary nectar thieves (honey bees) is poorly understood but seemingly unfavorable for V. ashei pollination. We designed two studies to measure the impact of nectar robbers on V. ashei pollination. First, counting the amount of pollen on stigmas (stigmatic pollen loading) showed that nectar robbers delivered fewer blueberry tetrads per stigma after single floral visits than did our benchmark pollinator, the southeastern blueberry bee, Habropoda laboriosa (F.), a recognized effective pollinator of blueberries. Increasing numbers of floral visits by carpenter bee and honey bee robbers yielded larger stigmatic loads. As few as three robbery visits were equivalent to one legitimate visit by a pollen-collecting H. laboriosa female. More than three robbery visits per flower slightly depressed stigmatic pollen loads. In our second study, a survey of 10 commercial blueberry farms demonstrated that corolla slitting by carpenter bees (i.e., robbery) has no appreciable affect on overall V. ashei fruit set. Our observations demonstrate male carpenter bees are benign or even potentially beneficial floral visitors of V. ashei. Their robbery of blueberry flowers in the southeast may attract more honey bee pollinators to the crop.

Ingestible insecticides for spotted wing Drosophila control: a polyol, Erythritol, and an insect growth regulator, Lufenuron

Bioassays tested insecticidal activity of Erythritol from the nutritive sweetener, Truvia, and an insect growth regulator, Lufenuron, against life stages (eggs, larvae, pupae, adults) of Drosophila melanogaster (Meigen) and Drosophila suzukii (Matsumura), the spotted wing Drosophila (SWD). These compounds were chosen for their demonstrated acute toxicity to adult and larval Drosophila and potential use on organic fruit farms. D. melanogaster fed on standard Drosophila diet media moistened with water containing known concentrations of Erythritol. Likewise, SWD consumed standard diet media as well as thawed host fruit (blackberries and blueberries) treated with solutions of Erythritol, Lufenuron or both. During the first bioassay, Erythritol at lower concentrations between 0 and 500 mm (~61 000 ppm) in water and mixed with instant diet media increased adult survival from ~80% to 97% for D. melanogaster and SWD. However, from aqueous concentrations ranging from 1750 (~414 000 ppm) to 2000 mm (~244 000 ppm), Erythritol killed 100% of adult Drosophila in culture vials. One hundred per cent mortality for SWD and D. melanogaster occurred at ≥0.5 m (~61 000 ppm) Erythritol added to diet media or topically applied to host fruit. In a second bioassay, 0.013–1.000 ppm of aqueous Lufenuron, a chitin synthase inhibitor, when added to dry diet media prevented 90–99% of SWD from reaching the pupal stage. In another assay, ~67% of SWD eggs or neonates (early first instars) died inside blackberries pre‐treated with (dipped in) a soapy solution of 10 ppm Lufenuron. Pre‐treating blackberry fruit with an Erythritol–Lufenuron mixture reduced SWD brood survival by 99%. Likewise, during our last fruit‐based bioassay, 98% of eggs and neonates died inside blueberries similarly pre‐treated. During the last experiment, Lufenuron in diet media also rendered adult females sterile. Sterility, however, dissipated over 7 days once females began feeding on a Lufenuron‐free diet media.

Erythritol and Lufenuron Detrimentally Alter Age Structure of Wild Drosophila suzukii (Diptera: Drosophilidae) Populations in Blueberry and Blackberry

Abstract We report on the efficacy of 0.5 M (61,000 ppm) erythritol (E) in Truvia Baking Blend, 10 ppm lufenuron (L), and their combination (LE) to reduce egg and larval densities of wild populations of Drosophila suzukii (Matsumura) infesting fields of rabbiteye blueberries (Vaccinium virgatum) and blackberries (Rubus sp.). Formulations included the active ingredients (lufenuron, erythritol, or both), sugar (in control and erythritol treatments), and Dawn hand-soap applied to plants with pressurized 3-gallon garden spray tanks. The three chemical treatments (E, L, and LE) had no effect on D. suzukii ovipositing in blackberry and blueberry fruit, but they did reduce larval infestation by 75%, particularly densities of first and second instars. Erythritol and lufenuron were equally efficacious compounds as a D. suzukii ovicide and larvicide, but they did not display additive or synergistic activity. Extremely high larval mortality in control fruits show an age structure heavily skewed toward egg output.

Biology and Efficacy of Aprostocetus (Eulophidae: Hymenoptera) as a Parasitoid of the Blueberry Gall Midge Complex: Dasineura oxycoccana and Prodiplosis vaccinii (Diptera: Cecidomyiidae)

ABSTRACT In the southeastern United States, bud-infesting larvae of two gall midge species, Dasineura oxycoccana (Johnson) and Prodiplosis vaccinii (Felt), destroy from 20 to 80% of the rabbiteye blueberry crop, Vaccinium virgatum Aiton (syn. V. ashei Reade). These midge larvae are attacked by five species of parasitoid wasps. The most effective of these is the bivoltine eulophid Aprostocetus sp. nr. marylandensis (Eulophidae), whose adults constitute one-third of the gall midge parasitoids, active in both conventional and organic blueberry fields. Broods of Aprostocetus use several reproductive strategies to keep sole possession of their larval hosts. As solitary endoparasitoids as well as facultative hyperparasitoids, precocial larvae of Aprostocetus devour hosts organs along with any younger siblings and rival parasitoid broods. Although larger hosts are preferred, any sized larvae can be parasitized, which reduces brood congestion and infanticide. An Aprostocetus female spends an hour or more in a systematic hunt for hosts, during which time 40 to 100% of midge larvae encountered are parasitized. Aprostocetus females could have located hosts more quickly had they recognized host-feeding scars as cues. Even so, high rates of larval parasitism achieved by Aprostocetus may kill as many midges as insecticides do.

Novel Aspects of Drosophila suzukii (Diptera: Drosophilidae) Biology and an Improved Method for Culturing this Invasive Species with a Modified D. melanogaster Diet

Abstract Drosophila suzukii (Matsumara) (Diptera: Drosophilidae), the spotted wing drosophila, is a global pest of soft fruits now rearable on a standard D. melanogaster (Meigen) diet containing the flys own natural food: soft-skinned berries. The techniques tested here can save 40% of cultures from microbial contamination that develops after combining artificial food sources (e.g., standard drosophila media) with unsterilized host plant material (berries). A suitable ratio for mixing dietary ingredients for a vial or test-tube rearing system includes, by weight, 1 part berry tissue for oviposition, 1.5 parts dry diet media for carbohydrate, 7 parts clean water for moisture, and ∼5 grains (0.8 mg) of dry yeast for protein. One or two blackberry or blueberry fruits used by spotted wing drosophila as edible oviposition substrates doubled and tripled pupal and adult production in standard 68 mL culturing vials. To prevent mold from spoiling the diet, the exocarp of berries was sterilized in an 80 or 90% ethanol bath at room temperature for ∼5 min, followed by a thorough rinsing with deionized water to remove residual alcohol, which can be acutely toxic to D. suzukii, a highly ethanol-intolerant species. Sterilized fruit and a larger fly population in vials disrupted the growth of microbial biofilms capable of suffocating adults. Identical body size in reared adults and locally caught wild flies of D. suzukii substantiates nutritional similarity between the fruit-media-based diet and the flys own natural food (i.e., whole berries). Triethylamine (50%), a common fly anesthetic, was acutely toxic to D. suzukii adults but not to D. melanogaster adults.

Laboratory and Field Assessments of Erythritol Derivatives on the Survival, Reproductive Rate, and Control of Drosophila suzukii (Diptera: Drosophilidae)

Abstract Spotted-wing Drosophila, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) is a vinegar fly introduced unintentionally into the United States. Since 2008, D. suzukii has reduced annual berry yields from 6 to 100%. Effective control of D. suzukii during harvest requires weekly applications of low-residual, broad-spectrum insecticides that are unavailable for organic farming. A novel ingestible insecticide, a 4-carbon polyol, mesoerythritol (erythritol), was found to kill 75 to 100% of larval and adult D. suzukii. However, mesoerythritol, at effective concentrations (0.5–1.0M), may be cost-prohibitive. Therefore, we conducted laboratory tests to assess the effects of lower cost derivatives of erythritol, namely the pentaerythritol series of 1,3-diols on D. suzukii pupal production, adult production, adult mortality, brood output, and reproductive increase. We then selected the two most promising compounds for a field test on fruiting rabbiteye blueberry. From 90 to 100% of adults died when fed food moistened with 1M solutions of mesoerythritol and pentaerythritol. Mesoerythritol and dipentaerythritol at a concentration of 1M were ovicidal/ larvicidal, killing ≥85% of immatures. Overall, 1M mesoerythritol killed 80% or more larvae and adults, thus bringing populations to near zero. The heaviest compound of this series, tripentaerythritol, at all concentrations, was largely benign to both adults and immatures. Thus, we cannot recommend tripentaerythritol for D. suzukii control. In a blueberry field, 0.5M mesoerythritol and 0.5M pentaerythritol, each by themselves, reduced egg infestation by 64% and larval infestation by 93%; their combination (0.25M mesoerythritol and 0.25M pentaerythritol) achieved even greater egg control with 82% fewer eggs infesting blueberry fruits.

Phenotypic Variation in Fitness Traits of a Managed Solitary Bee, Osmia ribifloris (Hymenoptera: Megachilidae)

ABSTRACT We investigated fitness in natural populations of a managed solitary bee Osmia ribifloris Cockerell (Hymenoptera: Megachilidae) from sites separated from 400 to 2,700 km. Parental wild bees originated in central Texas (TX), central-northern Utah (UT), and central California (CA). They were then intercrossed and raised inside a mesh enclosure in southern Mississippi (MS). Females from all possible mated pairs of O. ribifloris produced F1 broods with 30–40% female cocoons and outcrossed progeny were 30% heavier. Mitochondrial (COI) genomes of the four populations revealed three distinct clades, a TX-CA clade, a UT clade, and an MS clade, the latter (MS) representing captive progeny of CA and UT bees. Although classified as separate subspecies, TX and CA populations from 30° N to 38° N latitude shared 98% similarity in COI genomes and the greatest brood biomass per nest straw (600- to 700-mg brood). Thus, TX and CA bees show greater adaptation for southern U.S. sites. In contrast, UT-sourced bees were more distantly related to TX and CA bees and also produced ∼50% fewer brood. These results, taken together, confirm that adult O. ribifloris from all trap-nest sites are genetically compatible, but some phenotypic variation exists that could affect this species performance as a commercial blueberry pollinator. Males, their sperm, or perhaps a substance in their sperm helped stabilize our captive bee population by promoting legitimate nesting over nest usurpation. Otherwise, without insemination, 50% fewer females nested (they nested 14 d late) and 20% usurped nests, killing 33–67% of brood in affected nests.

‘Pearl’ Southern Highbush Blueberry

‘Pearl’ is a new southern highbush blueberry (Vaccinium spp. hybrid) developed and released by the United States Department of Agriculture Agricultural Research Service. The new cultivar has several advantages for growers in the Southeastern U.S. over rabbiteye blueberry cultivars, the most widely grown type of blueberry in the region. Among these are an earlier ripening period, high yield potential, and fruit quality. These attributes enable producers to participate in the lucrative early U.S. fresh market where opportunities for marketing rabbiteye blueberries have diminished due to expanding acreage in the region and other states.

Performance of Persimmon (Diospyros kaki) Cultivars in Southern Mississippi

The oriental persimmon is native to China and is best adapted to areas with moderate winters and relatively mild summers. However, because of its low chilling requirement, persimmons will break dormancy during early warm periods only to be damaged by spring frosts later. This study was initiated to determine suitable cultivars for the gulf coast region. ‘Hana Fuyu’ was greatly affected by a freeze event. ‘Fuyu Imoto’ and ‘Matsumoto’ had numerous smaller fruit and were less affected by freeze events. Results indicated that persimmon cultivars are available that would be a good addition to growers who would like to diversify their fruit selection in the southern U.S.