Comparison of Peach Cultivars for Provision of Extrafloral Nectar Resources to Harmonia axyridis (Coleoptera: Coccinellidae).

Incorporating nonprey sugar resources into apple orchards is a potential means of enhancing biological control services, but little is known about the impacts of extrafloral nectars on aphidophagous coccinellids. We explored peach Prunus persica (L.) Batsch extrafloral nectar as a supplemental resource for Harmonia axyridis (Pallas), a key aphid predator in the mid-Atlantic United States. Extrafloral nectar quantity, temporal production, and carbohydrate profile were assessed for four peach cultivars in orchard and greenhouse culture. Seasonal densities of H. axyridis visiting extrafloral nectaries were estimated, and the propensity of beetles to feed upon extrafloral nectar was compared by cultivar in the laboratory. We also compared survival of newly eclosed adult pairs that were starved or fed aphids with or without extrafloral nectar. Peach extrafloral nectar contained six carbohydrates, with sucrose dominant for all cultivars, but extrafloral nectar production varied significantly by cultivar and collection date, with 'Lovell' yielding higher average seasonal volume than the other cultivars. Harmonia axyridis continuously foraged on peach trees lacking prey, and beetle abundance was positively correlated with the number of leaves actively producing extrafloral nectar. In laboratory assays, newly emerged adult beetles preferentially selected and consumed extrafloral nectar of Lovell peach shoots. Furthermore, when prey were initially unavailable to adult H. axyridis, the beetles were sustained by extrafloral nectar and experienced longer survival compared with beetles without the supplemental resource. Collectively, these results suggest that peach extrafloral nectar is a beneficial resource that could potentially sustain H. axyridis in orchards when prey are scarce.

Identifying a Potential Trap Crop for a Novel Insect Pest, Halyomorpha halys (Hemiptera: Pentatomidae), in Organic Farms.

The invasive brown marmorated stink bug, Halyomorpha halys, poses significant risk to organic farming systems because they rely on biological control, nonsynthetic inputs, and cultural tactics for pest management. This study evaluated the potential of five crop plants (sorghum, admiral pea, millet, okra, and sunflower) to be used as trap crops under organic production in four mid-Atlantic states. Stink bug (H. halys and endemic species) densities and host plant phenologies were recorded weekly (mid-June through September). Sorghum attracted significantly more H. halys than the other crops evaluated, followed by sunflower and okra. Seasonal average H. halys density was 1.5-4× higher on sorghum than the other crops (P < 0.05), depending on site. Endemic stink bugs were equally attracted to all crops except admiral pea. A significant effect of time was detected (P < 0.0001), with H. halys densities initially higher on sunflower; as the sunflower senesced, sorghum supported significantly higher average H. halys densities. While sunflower and sorghum phenologies differed, these crops together provided a 5-wk attraction period coinciding with peak H. halys activity. The efficacies of pheromone-baited traps, flaming, applying OMRI-approved insecticides (Azera and Venerate), and vacuuming to removing stink bugs were evaluated as a management tactic. Flaming was the most effective treatment against H. halys and endemic stink bugs. Our results suggest that a trap crop composed of sorghum and sunflower may be an effective management tool for the mid-Atlantic stink bug complex, including H. halys. Future research should address the appropriate size and placement of trap crop within the farm.

Interactions between extrafloral nectaries, ants (Hymenoptera: Formicidae), and other natural enemies affect biological control of Grapholita molesta (Lepidoptera: Tortricidae) on peach (Rosales: Rosaceae).

Extrafloral nectaries (EFNs) are reported to benefit some plants when ants (Hymenoptera: Formicidae) use their secretions and fend off herbivores, but in some cases resulting competitive interactions may reduce biological control of specific herbivores. This research examined the interactions between ants and other natural enemies associated with the EFNs of peach [Prunus persica (L.) Batcsh] and the implications for biological control of a key pest, the oriental fruit moth [Grapholita molesta (Busck)]. Studies using sentinel G. molesta placed on peach trees ('Lovell' cultivar) with EFNs present and absent revealed that several natural enemy groups associated with the EFNs contribute to reductions in G. molesta eggs, larvae, and pupae in peach orchards. Ants on trees with EFNs antagonized the G. molesta egg parasitoid Trichogramma minutum (Riley), but the ants were crucial in reducing G. molesta in both the larval and pupal stages. Overall, individual trees with EFNs experienced higher ant and other (nonant) natural enemy densities and subsequent pest reductions, as compared with trees without EFNs. However, the implications of EFN-natural enemy-pest interactions to orchard-level biological control will likely depend on local G. molesta population dynamics.

Extrafloral nectar in an apple ecosystem to enhance biological control.

A common goal of conservation biological control is to enhance biodiversity and increase abundance and effectiveness of predators and parasitoids. Although many studies report an increase in abundance of natural enemies, it has been difficult to document increases in rates of biological control. To enhance parasitism of the tufted apple bud moth, Platynota idaeusalis (Walker) (Lepidoptera: Tortricidae), alternate food was provided by interplanting peaches bearing extrafloral nectaries into apple (Malus spp.) orchards. Laboratory studies showed that the presence of nectar increased longevity and parasitism rates by Goniozus floridanus (Bethylidae), the dominant parasitoid of tufted apple bud moth in West Virginia. In orchard studies, we found the total number of hymenopteran parasitoids was higher on peach (Prunus spp.) trees than on adjacent apple trees. Abundance of parasitic Hymenoptera also was significantly higher on the side of traps facing away from rather than toward peach trees, indicating attraction to peach trees. However, total parasitism rates of tufted apple bud moth were not affected by the presence of peach extrafloral nectar in any field studies. Insect injury to fruit at harvest showed that fruit from orchards with interplanted peach trees had less injury from San Jose scale, Quadraspidiotus perniciosus (Comstock) and stink bugs (Pentatomidae) than fruit from an apple monoculture. Although interplanting with peach trees did not produce the hypothesized result of increased biological control, the experiment did have beneficial results for pest management. These results demonstrate the importance of collecting data on variables beyond the targeted species when evaluating habitat manipulation experiments to fully assess the impact on the ecosystem.

Extrafloral nectaries alter arthropod community structure and mediate peach (Prunus persica) plant defense.

We investigated the role of extrafloral nectaries (EFNs) in mediating plant defense for newly established peach (Prunus persica) trees. We used peaches of a single cultivar ("Lovell") that varied with respect to EFN leaf phenotype (with or without EFNs) to determine if the EFNs affected the structure of the arthropod community colonizing newly planted seedlings. We also tested if the plants producing EFNs benefited from reduced herbivory or enhanced productivity. In the first year following planting, the young peach trees with EFNs were dominated by ants, and arthropod community diversity was lower than for trees without EFNs. The young trees with EFNs harbored fewer herbivores and experienced a twofold reduction in folivory compared to trees without EFNs. Productivity was also enhanced for the trees with EFNs, which attained significantly higher rates of trunk growth, greater terminal carbon composition, and a threefold increase in buds produced in subsequent years. In the second year of the field study, ants remained numerically dominant on trees with EFNs, but arthropod community diversity was higher than for trees without EFNs. An additional study revealed that folivory rates in May increased dramatically for trees with EFNs if ants were excluded from their canopies, indicating that ants have a protective function when the perennial trees produce new leaves. However, in later months, regardless of ants' presence, the trees with EFNs suffered less folivory than trees lacking EFNs. The diversity and richness of the predator trophic group increased when ants were excluded from trees with EFNs, but overall community diversity (i.e., herbivores and predators combined) was not affected by the ants' presence. Our research indicates that the EFNs play an important role in attracting predators that protect the trees from herbivores, and the EFN host-plant characteristic should be retained in future peach cultivar selections. Furthermore, peach production programs aimed at reducing insecticide inputs should seek to incorporate peach cultivars with EFNs, to optimize the potential for naturally occurring biological control agents to protect the trees from herbivores.

Leaf extrafloral nectaries enhance biological control of a key economic pest, Grapholita molesta (Lepidoptera: Tortricidae), in peach (Rosales: Rosaceae).

Extrafloral nectaries (EFNs) in many plant species produce sugary secretions that commonly attract ants. This research determined the impact of peach (Prunus persica L. Batsch) EFNs on the biological control of the oriental fruit moth, Grapholita molesta (Busck) (Lepidoptera: Tortricidae), a key economic pest in peach orchards, and studied interactions of EFNs and ants. Studies (2002-2005) in peach orchards of the mid-Atlantic United States showed that 'Lovell' peach trees with EFNs supported more parasitic Hymenoptera in the spring and increased the parasitism of G. molesta larvae later in the season than those trees without EFNs. Ant exclusion experiments revealed that trees with EFNs harbored fewer G. molesta larvae when ants were permitted access to the tree canopies. Furthermore, the trees with EFNs had approximately 90% less fruit injury by G. molesta, indicating that EFNs have a protective role for the fruit as well. The results show that the combined actions of ants and parasitic Hymenoptera confer an EFN-mediated protective effect spanning the whole fruit growing season. When EFNs are present, naturally occurring biological control agents can reduce damage by G. molesta in peach orchards without insecticide inputs. The EFNs are an important host-plant characteristic that should be retained in future peach cultivar selections as a means of enhancing biological control.

Conservation biological control of rosy apple aphid, Dysaphis plantaginea (Passerini), in eastern North America.

Because of the potentially serious damage rosy apple aphid, Dysaphis plantaginea (Passerini) (Homoptera: Aphididae), can cause to apple fruit and branch development, prophylactic insecticides are often used for control. If biological control could be relied on, the amount of pesticide applied in orchards could be reduced. This study examined biological control of rosy apple aphid in eastern West Virginia and the potential for enhancement through conservation biological control, in particular, the effect of interplanting extrafloral nectar-bearing peach trees. By 20 d after first bloom, only 2% of fundatrices initially present survived to form colonies based on regression of data from 687 colonies. Exclusion studies showed that many of the early colonies were probably destroyed by predation; the major predator responsible seemed to be adult Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae). Mortality before apple bloom was most important in controlling rosy apple aphid population growth but by itself is not sufficiently reliable to prevent economic injury. Interplanting of extrafloral nectar-bearing trees did not increase biological control, and interplanting with 50% trees with extrafloral nectar glands reduced biological control. The number of leaf curl colonies in the 50% interplanted orchards was lower than in monoculture orchards, suggesting a preference of alate oviparae for more diverse habitats, supporting the resource concentration hypothesis but not at a level sufficient to prevent injury. Predation and parasitism after the formation of leaf curl colonies was not adequate to control rosy apple aphid populations.