Leaf‐derived cecidomyiid galls are sinks inMachilus thunbergii(Lauraceae) leaves

Abstract

Three relevant hypotheses - nutrition, environment and the enemies hypothesis - often invoked to explore source and sink relationships between galls and their host plants are still under dispute. In this research, chlorophyll fluorescence, gas exchange capacity, stomatal conductance, total carbon and nitrogen, total soluble sugars and starches, and scanning and transmission electron microscopy of two types of galls were used to investigate source-sink relationships. Compared with host leaves, these galls demonstrated slightly lower chlorophyll fluorescence; however, gas exchange capacity and stomatal conductance were not detected at all. Scanning electron micrographs demonstrated that the abaxial epidermis of host leaves contain normal amounts of stomata, whereas no stomata were observed on the exterior and interior surfaces of both types of galls. In addition, gall inner surfaces were covered with many kinds of fungal hyphae. Gall total carbon (C) and nitrogen (N) levels were lower but the C/N ratio was higher in galls than host leaves. Both types of galls accumulated higher total soluble sugars and starches than host leaves. Transmission electron micrographs also revealed that both types of galls contain plastoglobuli and giant starch granules during gall development. Results strongly indicate that leaf-derived cecidomyiid galls are sinks in Machilus thunbergii leaves. However, it is perplexing how larvae cycle and balance CO(2) and O(2) in gall growth chambers without stomata.

Sink Status and Photosynthetic Rate of the Leaflet Galls Induced by Bystracoccus mataybae (Eriococcidae) on Matayba guianensis (Sapindaceae)

“…This pattern was observed in the horn-shaped gall induced by a Cecidomyiidae on Copaifera langsdorffii (Castro et al, 2012), and in the ovoid and obovate galls induced by Daphnephila taiwanensis and D. sueyenae (Cecidomyiidae) on Machilus thumbergii (Huang et al, 2014). Nevertheless, some galls do not cause significant changes in the photosynthesis of their host organs, as the galls induced by the aphid Melaphis rhois on Rhus glabra (Larson, 1998), and by the psyllid Pseudophacopteron aspidospermi on Aspidosperma australe (Oliveira et al, 2011; Malenovský et al, 2015).…”

“…These sinks drain nutrients from other plant parts (Mani, 1964; Castro et al, 2012; Huang et al, 2014), which is especially true for galls induced by sucking insects. The feeding activity of these insects in specific plant tissues (e.g., the phloem) affects the carbon-partitioning mechanisms within the host plant compartments, and alters the balance among source and sink tissues.…”

“…Galls induced by Cecidomyiidae (Diptera) can cause a decrease in photosynthetic rates (Andersen and Mizell, 1987; Larson, 1998; Florentine et al, 2005; Huang et al, 2014), and function as strong sinks of photoassimilates from their host leaves. This pattern was observed in the horn-shaped gall induced by a Cecidomyiidae on Copaifera langsdorffii (Castro et al, 2012), and in the ovoid and obovate galls induced by Daphnephila taiwanensis and D. sueyenae (Cecidomyiidae) on Machilus thumbergii (Huang et al, 2014).…”

Insect Gallers and Their Plant Hosts: From Omics Data to Systems Biology

“…Gall-inducing insects are able to manipulate the source-sink dynamics within their hosts and reconfigure their host’s metabolism [14,23,24,25,26,27,28,29]. Transcriptomic studies of a variety of plant-galling insect interactions have described general up-regulated expression of primary metabolism and nutrient transport in the plant, as well as down-regulation of defence-associated processes.…”

Morphometric analysis of young petiole galls on the narrow-leaf cottonwood, Populus angustifolia, by the sugarbeet root aphid, Pemphigus betae

“…The lack of intercellular spaces indicates the occurrence of little gas exchange and consequent reduced photosynthetic metabolism (Carneiro and Isaias 2015a). Chloroplasts and mitochondria are numerous and poorly differentiated, often leading to photosynthesis-deficient cells within the galls (Bronner 1992; Huang et al 2014; Carneiro and Isaias 2015a). Understanding these insect-induced cytological changes may help elucidate how the insect induces gall formation.…”