Occurrence and characterization of insect galls in two reserves of the Peruvian Amazon

An insect gall inventory was carried out in two reserves of the Peruvian Amazon, Allpahuayo-Mishana National Reserve and Quistococha Regional Reserve, both situated in Iquitos, northeastern Peru. Four vegetation types were surveyed between December, 2021 and December, 2022: terra firme forest, white-sand wet forest, and white-sand dry forest in Allpahuayo-Mishana National Reserve, and palm swamp forest in Quistococha Regional Reserve. Overall, we found 262 gall morphotypes, distributed across 75 host species representing 66 plant genera and 30 families. Fabaceae was the plant family with the greatest number of gall morphotypes (n = 48), followed by Calophyllaceae (n = 21) and Euphorbiaceae (n = 20). The plant genera that supported the highest diversity of galls were Caraipa (n = 17), Eschweilera (n = 16), Tapirira (n = 16), Micrandra (n = 14), and Iryanthera (n = 10). The plant species Tapirira guianensis (n = 16), Caraipa utilis (n = 14), Micrandra elata (n = 14), Eschweilera coriacea (n = 11), and Sloanea parvifructa (n = 10) exhibited the highest richness of galls. Among the host plants, C. utilis stands alone as the only species noted as both endemic to the Amazonian region and bearing a Vulnerable (VU) conservation status. The leaves were the most attacked organs (90% of all galls). Most morphotypes are glabrous (89%), green (67%), globoid (53%), and one-chambered (91%). We found galling insects belonging to the orders Diptera, Thysanoptera, Lepidoptera, and Hemiptera. The galling insects of Cecidomyiidae (Diptera) were the most common, inducing 22% of the gall morphotypes. In addition to the gallers, we also observed the presence of successors, cecidophages, and parasitoids. Among the sampled vegetation types, the terra firme forest presented the highest richness of gall morphotypes and host plant species. This is the first systematic inventory of insect galls in this part of the Peruvian Amazon.