Efficiency of trap- catching and killing spiraea aphids by yellow sticky cards

Abstract:【Objective】Yellow sticky card is a common physical control method used in agriculture, and their efficacy is based on the attraction of pests to bright colors. In the present experiment, we revealed the number and identity of different species trapped by yellow sticky cards, so as to evaluate the effica- cy of this method for controlling spiraea aphids in practical production【. Methods】The yellow sticky card trapping experiment was conducted from March 2, 2019 to September 7, 2019 in the apple orchard of Luochuan Apple Station, Northwest A & F University, in Yan’an city. Ten yellow sticky cards ar- ranged in a W-shaped pattern were hung in the periphery of the apple tree canopy, at a height of approxi- mately 1.8 m. The yellow sticky cards were changed every seven days. The control effect was deter- mined by counting the number of species and insects trapped and calculating the ratio of beneficial in- sects to pests. Specifically, target pests were distinguished from non-target pests, predatory natural ene- mies, flies and bees. The beneficial insect/pest ratio was calculated by a natural enemy unit that con- tained one adult and one larva of a ladybird feeding on aphids or one lacewing fly and one syrphid fly.【Results】The number of target pests trapped was (109.9±5.1) per card, while the number of leafhop- pers, scarabs and psyllas trapped was (234.2±5.7), (47.8±6.6) and (3.9±0.6) per card, respectively. The number of syrphid flies, ladybirds, Chrysopa and serpentines trapped was (47.2±4.0), (39.6±6.7), (17.8± 2.2) and (18.4±6.3) per card, respectively. Additionally, yellow sticky cards were also effective in cap-turing flies. The number of Drosophilid, Sarcophaga and Calliphora captured was (394.4 ± 40.2), (231.8±19.8) and (11.4±1.4) per card, respectively. The number of honeybees trapped was (22.1±1.6) per card, and most of them were trapped during the flowering stage. The control of the target pest (aphids) by yellow sticky cards was limited; the number of non-target pests trapped exhibited in the fol- lowing descending order: leafhopper > scarab > woodlouse; the ranking order for the number of predato- ry natural enemies trapped was ladybird > aphid > snake wing > chrysopanax. This strong trapping ef- fect on predatory natural enemies suggested that yellow sticky cards should not be used in orchards with ideal ecological conditions and high population densities of predatory natural enemies. Additional- ly, the number of flies trapped exhibited the following order: Drosophila > Sarcophaga > Calliphora, indicating that the yellow sticky cards also had a trapping efficacy on bees. Thus, yellow sticky cards should not be used during the apple flowering period to allow better bee pollination. The yellow sticky card was a broad-spectrum physical control measure. It had trapping effects on target pests, non-target pests and natural enemies. The beneficial insect/pest ratio of the yellow sticky card was 1∶1.2. From March 2, 2019 to September 7, 2019, only (88.1±3.6) winged aphids were trapped by each yellow sticky card in the Luochuan apple production area. The population density of winged aphids was also a factor affecting the number of insects trapped by yellow sticky cards. Outbreaks of aphids were most likely to occur under high-temperature and drought conditions; frequent use of pesticides leads to in- creasing resistance, resulting in a decline of the chemical control effect. Additionally, the population density and the degree of protection provided by predatory natural enemies also affect the population density of aphids. Generally, yellow sticky cards should only be used to monitor the population densi- ties of winged aphids and detect aphid outbreaks. Because ladybugs, Chrysopa, snake flies and aphid flies primarily fed on wingless apple aphids, the trapping of natural enemies by yellow sticky cards was inevitable, reducing the efficacy of biological control. Therefore, the control of aphids by yellow sticky cards needed to be improved. During outbreaks, wingless forms of aphids often dominated and conse- quently, chemical control was also needed to achieve their rapid control. Under suitable ecological con- ditions, the total number of winged aphids captured was relatively low, which may also explain the num- ber of winged aphids trapped by yellow sticky cards. The color, size, hanging height, viscosity and hanging density of yellow sticky cards could also affect their ability to trap target pests.【Conclusion】The control of aphids by yellow stick cards was not effective, as other non-target pests may also be at- tracted to these traps. Several aspects needed to be evaluated to make yellow stick cards suitable for use in agriculture at a large scale. Trapping by yellow stick cards was a broad-spectrum measure that may affect the population densities of bees and natural enemies under natural conditions. Yellow sticky cards should not be used in orchards during the apple flowering period or in areas with high population densi- ties of natural enemies. The effective period for hanging yellow sticky cards in the Luochuan apple pro- duction area was from early May to mid-July, and the duration of yellow sticky card hanging for aphid control should be designed accordingly. A comprehensive analysis revealed that the hanging of yellow sticky cards in Luochuan apple orchard had more disadvantages than advantages in terms of its control effect, economic cost, labor cost and impact on natural enemy insects. The optimal density and spacing of yellow sticky cards, as well as their influences on natural enemies and pest control, likely depended on the time of year and varied in different regions. Thus, these aspects need to be evaluated to optimize their application.