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Volatiles and habitat management to support the functional response of natural enemies

Tilrettelegging for nytteinsekt mot skadedyr ved bruk av biologisk mangfold og luktstoffer_GT

Lacewings Chrysoperla carnae s.l. (middle) are important natural enemies of pest insects used in biological pest management. Volatile dispensers (left) and odour paste (right) containing plant volatiles which are attracting lacewings and increase aphid control in cereals. 

Photos: Gunda Thöming

A rich biodiversity is required to provide good habitats for insects, and this is a key for good ecosystem services, such as biological pest management. Current research shows that habitat management to support natural enemies combined with the use of volatiles that increase the functional response of these beneficials can result in an even more effective and resilient biological pest management.

In Norway we have a lot of good possibilities to manage our agricultural landscape in a way that help beneficial insects. We must ensure good habitats for beneficials with adequate food, shelter, and places to overwinter in our agricultural landscape. Thereby beneficials can establish, participate efficient in pest management, and reduce the need for traditional chemical pesticides.

In collaboration with farmers, we established a pest management strategy which combines plant volatiles, floral field edges and overwintering places to support lacewings. Lacewings are important natural occurring beneficial insects, which are used to control i.a. aphids. Lacewings have as many other insects a very sensitive sense of smell.

In collaboration with colleagues in Hungary we have developed a volatile blend which attracts lacewings and increases their egg laying. Using these volatiles in the field results in an increased number of hungry lacewing larvae, which are feeding on pest insects and thus, increasing biological pest control. The volatile blend is imitating the odour from plants which are attacked by pest insects. The plant is using these volatiles as SOS-signal and lacewings use these cues to find an optimal place for the next generation.

Together with the Semiochemical industry in the US and researcher in Sweden  we have tested a biodegradable odour paste for biological management of i.a. aphids. After four years field experiments in cereals, we have seen that a pest management strategy combining plant volatiles, floral field edges and overwintering places to support lacewings is able to increase biological control of aphids. The amount of lacewings has increased while the amount of aphids was kept bellow the economic damage threshold. The use of traditional chemical pesticides has been reduced substantially.



Conservation biological control (CBC) is a promising tool for ecological intensification that aims to establish resilient natural enemy populations that contribute to pest management with reduced use of pesticides and at the same time support native biodiversity in agroecosystems. Yet the impact of natural enemies in CBC is often limited due to missing resources such as food, habitat, and hibernation shelters. Here, we studied a CBC strategy that incorporates these essential resources combined with semiochemicals, focusing on how the common green lacewing can enhance biological control of aphids. In a 4-year field study conducted at three locations in the region of East Norway, we developed a CBC strategy combining the three measures ATTRACT (a ternary attractant that increase lacewing egg laying), FOOD (floral buffer strips), and SHELTER (insect hotels for overwintering survival) to increase aphid biological control in spring barley. We recorded the number of lacewings, ladybirds, hoverflies, parasitized aphid mummies, and the two cereal aphid species Sitobion avenae and Rhopalosiphum padi. Our CBC strategy resulted in a significant increase in lacewing activity and significant aphid suppression. At all three locations and over the 4-year period, aphid infestation was below the economic damage threshold in the field plots using CBC measures. In contrast, during two of the years, the density of the aphid infestation in the control plots was significantly above the damage threshold. We found evidence that use of the ternary attractant supported green lacewings but led to loss of ladybirds, hoverflies, and parasitoids, even though flower strips were used as alternative resources. Our study shows a promising increase in lacewing activity in the agricultural landscape and high biological control of aphids in barley. Long-term field studies are needed to evaluate the impact on non-target species and the agroecosystem before practical application of this approach can be considered.

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Upon herbivory, plants release herbivore-induced plant volatiles (HIPVs), which induce chemical defenses in the plant as well as recruit natural enemies. However, whether synthetic HIPVs can be employed to enhance biological control in a cultivated crop in the field is yet to be explored. Here we show that a biodegradable formulation loaded with induced and food-signaling volatiles can selectively recruit the common green lacewing, Chrysoperla carnea, and reduce pest population under field conditions. In apple orchards, the new formulation attracted lacewing adults over a 4-week period, which correlated well with independent assessments of the longevity of the slow-release matrix measured through chemical analyses. In barley, lacewing eggs and larvae were significantly more abundant in treated plots, whereas a significant reduction of two aphid species was measured (98.9% and 93.6% of population reduction, for Sitobion avenae and Rhopalosiphum padi, respectively). Results show the potential for semiochemical-based targeted recruitment of lacewings to enhance biological control of aphids in a field setting. Further research should enhance selective recruitment by rewarding attracted natural enemies and by optimizing the application technique.