Multitrophic Interactions Between Arbuscular Mycorrhizal Fungi, Foliar Endophytic Fungi and Aphids

Almost all living plants can be simultaneously colonised by arbuscular mycorrhizal fungi in the roots and endophytes in the shoots, while also being attacked by insect herbivores. However, to date, no study has ever examined the multitrophic interactions between these two different fungal groups and insects on any species of forb. Here, we examined the effects of two commercial species mixtures of arbuscular mycorrhizal fungi (AMF) and two foliar endophytes (Colletotrichum acutatum and Cladosporium oxysporum) on the growth of an invasive weed, Impatiens glandulifera, and the aphids that attack it. AMF reduced plant biomass, which was most evident when C. oxysporum was inoculated. Mycorrhizal fungi had few effects on aphids, and these depended on the identity of the endophytes present. Meanwhile, endophytes tended to increase aphid numbers, but this depended on the identity of the AMF inoculum. Throughout, there were differences in the responses of the plant to the two mycorrhizal mixtures, demonstrating clear AMF specificity in this plant. These specific effects were also strongly affected by the endophytes, with a greater number of interactions found between the AMF and endophytes than between the endophytes themselves. In particular, AMF reduced infection levels by the endophytes, while some endophyte inoculations reduced mycorrhizal colonisation. We suggest that both AMF and endophytes could play an important part in future biological control programmes of weeds, but further multitrophic experiments are required to unravel the complexity of interactions between spatially separated parts of the plant microbiome.

Multitrophic Interactions Between Coccinellids and Their Parasitoids in Natural and Managed Plant Systems: Host Plant and Aphid Prey Species Matter

Background: To better inform conservation biological control of aphids multitrophic interactions between aphids, coccinellids and their parasitoids in natural and managed plant systems were examined over 4 years. Methods: Coccinellid larvae found naturally feeding on aphids on two non-crop plants growing in agricultural landscapes in Pakistan; Aphis nerii (Boyer de Fonscolombe) feeding on Calotropis procera L. and Nerium oleander L.; and four crop host; Lipaphis erysimi (Kalt) feeding on Eurica sativa Mill. and Brassica campestris L., Uroleucon compositae (Theobold) feeding on Carthamus tinctorius L., and Diuraphis noxia (Mordvilko) feeding on Hordeum vulgare L.; were collected throughout the aphid season and reared on their respective aphid-plant combination in the laboratory to identify coccinellid species, their parasitoids and performance (survival and pupal weight).Results: Coccinellid pupal weight on different host plant-aphid combinations varied from 3.4±1.8 to 11.2±0.9 mg (mean ± SE), as did mortality of coccinellid larvae due to diseases and unknown causes (5±2.2 to 31±3.8%). Parasitism of coccinellid larvae by Homalotylus flaminus (Dalman) (Hymenoptera: Encyrtidae) ranged from ca 10±2 to 30±3% in B. campestris and E. sativa, respectively. Parasitism of coccinellid pupae by Oomyzus scaposus (Thomson) (Hymenoptera: Eulophidae) ranged between 17±2.7 (C. procera) to 41±2.9% (B. compestris). One Dinocampus coccinellae Schrank (Hymenoptera: Braconidae) was reared. Conclusions: Coccinellids were host plant and aphid selective. Some coccinellids were never or rarely recorded on a particular aphid-plant combination, suggesting that their prey selection more specific than often assumed. Management decision and conservation biological control cannot be based on superficial categories such as “aphids” and “coccinellids” but needs to be plant and species specific.