Conservation biological control of arthropods using artificial food sprays: Current status and future challenges

The use of artificial food sprays to increase the abundance and impact of natural enemies of arthropod pests has been recognized for over 40 years. Nevertheless, artificial food sprays are applied in relatively few conservation biological control programs, possibly because of inconsistent performance. To consider this explanation, using a hierarchical classification approach ranging from altered foraging behavior at the simplest level to profitability of farm production at the highest level, we quantitatively reviewed 234 trials from 77 publications. The levels of assessment of food sprays most commonly found in the publications were the densities of arthropod pests (59 trials) and their natural enemies (124). Although the density of natural enemies increased in 108 of the 124 trials (or 87% of cases) and pest populations declined in 28 of the 59 trials (or 47%), increased profit was not demonstrated in the five trials where it was examined. The most commonly studied natural enemies belonged to the order Neuroptera (104 trials). Nevertheless, the parasitic Hymenoptera had the highest proportion of positive successes (56 of the 69 trials or 81%). Contrary to predictions, the likelihood of a successful result was not affected by the duration of food spray provision, management intensity, application frequency, or replenishment interval. However, success was more likely as spray concentration increased. When analyzed separately, the Coleoptera showed the greatest response to carbohydrates alone, such as honey and sucrose, compared with a mixture of carbohydrates and proteins. To achieve greater success with artificial food sprays, and therefore overcome a major impediment to their adoption, we contend that researchers should: (i) demonstrate greater success across several levels in the hierarchy, especially profit; (ii) consistently demonstrate success in field trials replicated across regions and years; and (iii) combine artificial food sprays with other compatible elements of an integrated pest management strategy. Until these outcomes are demonstrated, it is envisaged that artificial food sprays will form only a small part of future conservation biological control programs.