As I’ve mentioned before, lacewings may have complex preferences on the prey they eat, even if they are generalists. These preferences would be extremely useful to take note of – if you are trying to control a specific taxa of pest, it’s important to know which species of predator will not only eat them, but do so with focused effort.
This article observes the prey preferences of 3rd instar Chrysoperla carnea between two common pest species: lettuce aphids (Nasonovia ribisnigri) and western flower thrips (Frankliniella occidentalis).
Both of these pest species are significant pests of lettuce, categorized as r-selected species, meaning they produce a large number of lower quality offspring extremely quickly, with both experiencing parthenogenesis and short generation length. F. occidentalis scars edible leaves, causing rib discoloration, while N. ribisnigri can cause leaf distortion and reduce seedling effectiveness. Both can act as a source of viral plant disease, as well as reducing cosmetic quality of produce.
A circular lettuce leaf disk was placed in the bottom of a petri dish, and five prey ratios were tested with 10-15 replicates. The ratios were 10 aphids :80 thrips, 25:65. 45:45, 65:25, and 80:10. Additionally, controls with no C. carnea were carried out.
Results and Discussion
C. carnea readily preys upon N. ribisnigri and F. occidentalis. The article mentions that the maximum predation rate occurs at the ratio of the highest number of the two species (42 aphids : 71 thrips in this case), which I hypothesize is based upon less need for search and recognition due to higher prey densities, something that was touched upon briefly in Limburg, D. D., & Rosenheim, J. A. (2001), which I discussed a couple of posts ago.
They also discuss how much predation occurs per day, with their experiment observing 230 N. ribisnigri per a 16 : 8 photoperiod, although they state this may be optimistic as the larvae they used hadn’t eaten in preparation for this trial. They expect that 380 F. occidentalis can be eaten a day, however this also seems high compared to other studies, albeit they were observing single prey systems and therefore cannot be compared directly. Hunger levels and temperature can also play a large role in the voracity of the larvae, so that should be noted as well.
C. carnea exhibited a large preference for N. ribisnigri over F. occidentalis in two ratios (aphids:thrips), 10:80 and 65:25, however no significant preference was observed in the other ratios. There is no good, obvious explanation for this observation. Overall, across all ratios, there was some preference for N. ribisnigri over F. occidentalis, signifying that preference change was not necessarily related to the changing ratios of prey species. This could also be a result of using starved third instar larvae, whos hunger responses may have led them to ignore prey preferences.
Based on this research and earlier studies (Tulisalo (1984), Advashkevich et al. (1972)), they assert that C. carnea exhibits some preference to eating aphids, which could be a result of it being higher quality food, its larger size and relative immobility, or a reaction to chemical cues created by N. ribisnigri. This would be in line with some of my research in Insect Bioecology, as Chrysopidae are attracted to some plant volatiles aphids can ingest, as well as honeydew and aphid sex pheromones.
Ultimately, more research would be helpful in further determining prey preference, and it is also affected by the host plants defenses and architecture to some extent, so that should be kept in mind as well.