Natural enemy (NE) biodiversity is thought to play an important role in agricultural pest suppression. However, the relative importance of the number of NE species (species richness), versus the particular combinations of species (species composition), in determining aphid suppression and ultimately crop yields, remains poorly understood. We tested the effects of NE richness and composition on pea aphids Acyrthosiphon pisum (Harris) and broad bean plants Vicia faba (Linn.). We used the larvae of two predator species, the ladybird Adalia bipunctata (Linn.) and the green lacewing Chrysopa carnea (Stephens), and the parasitic wasp Aphidius ervi (Haliday) as enemies. NEs generally reduced aphid density but did not increase final plant biomass, despite a significant negative correlation between aphid density and plant biomass. Among NE treatments, species richness had an inconsistent effect on aphid density. The composition of NEs within richness levels also affected final aphid density: the ladybird was a key species among the treatments in controlling aphid density and was especially effective in combination with the parasitoid. This ladybird/parasitoid combination also appeared to drive the higher level of suppression observed at the two, relative to three, species richness levels. Although these three species of aphid NEs are commonly used in aphid control, this is the first study, to our knowledge, that simultaneously examined these three species and highlighted the composition effect between the A. bipunctata and A. ervi. In conclusion, increasing NE species richness had an inconsistent effect on aphid density. Meanwhile, the presence of a key species (the ladybird) and its combination with a parasitoid was an important determinant of aphid biological control.

Many studies demonstrate an important role of natural enemy biodiversity in the regulation of agricultural pests, but the role of different aspects of biodiversity in influencing this crucial ecosystem service remain controversial. We hypothesised that the functional diversity generated by combining divergent consumer groups (roaming coccinellid predators and parasitoid wasps) fosters complementarity, enhancing aphid biocontrol. We tested this using experimental mesocosms containing plants, aphids and natural enemies located in a greenhouse. We compared the aphid control efficiency (final aphid abundance) of low functional diversity treatments (two parasitoid species, or two predator species) with high functional diversity treatments (all four possible predator-parasitoid combinations). We also included all four enemies as single species treatments to allow calculation of the non-additive effects of combining natural enemies. Results showed that biocontrol (final aphid abundance) was driven by the species identity of natural enemies and positive non-additive effects in two treatments in which the most efficient predator species was combined with a parasitoid species and the other predator species, respectively. Functional diversity did not consistently influence biocontrol or non-additive effects. In conclusion, functional diversity, as defined by differences between roaming predator and parasitoid functional groups, failed to consistently explain biocontrol efficiency in our study. This calls for consideration of finer-scale functional traits and how they govern natural enemy interactions and cascading effects across ecosystems.

Insect pest management has been dominated by the use of synthetic pesticides since early 1950s. However, lately this control method is not widely accepted due to an increase in environmental awareness, food safety concerns and the increasing number of insecticide-resistant species. In Iraq, the chemical insect pest control is still a dominant control method regardless of the increased pressure to replace it gradually with environment friendly alternatives such as predators, parasitoids, nematodes and entomopathogenic fungi. In Iraq, there is an increasing volume of research that has used different genus and species of entomopathogenic fungi for controlling several agricultural pests. However, these efforts are not yet reflected in the industry. In this short review article, a detailed summary of the research that has been done with entomopathogenic fungi in Iraq since 2000 is given and a brief discussion of the potential of using entomopathogenic fungi on a large scale in Iraq, its challenges, and recommendations is presented.