Oak (Acorn)–Weevil Interactions across an Extensive Latitudinal Gradient in Eastern North America

Michael A Steele,Shealyn Marino,Andrew W Bartlow,Rachel Curtis,Jeffrey A Stratford,Harmony J Dalgleish

doi:10.3390/d13070303

Michael A Steele, Shealyn Marino + Show 4 more

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https://doi.org/10.3390/d13070303

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Abstract

Recent studies have explored how nut weevils (Curculio and Conotrachelus spp. (Coleoptera: Curculionidae) prey on the fruits (acorns) of oak (Quercus spp.). However, few, if any, have examined these interactions over both an extensive geographic area and over several years. Here, we observed patterns of infestation in acorns of both red oak (Quercus rubra) and white oak (Quercus alba) over an eight-year period along a latitudinal transect, extending as far as 900km, across much of the shared range of these two oak species. Although weevil prevalence did not differ significantly between the two oak species, in red oak, infestation prevalence increased significantly with latitude. In contrast, an opposite pattern was evident in white oak, with the highest infestation prevalence occurring at lower latitudes. One controlled measure of cotyledon damage was significantly lower in acorns of red oak than those of white oak, which may in part be due to larger acorn size at the lower latitudes. Future investigations in this system should focus on the distribution of weevil species (with DNA barcoding) across this range and geographic variation in chemical gradients that likely determine patterns of weevil damage in individual acorns.

Highlights

The oaks, which includes ~350–500 species worldwide, are distributed widely across the globe from northwestern South America, through Central America, North America including Mexico, Europe, the northwestern edge of Africa, and much of eastern Asia [1,2,3,4]
We sampled acorns from adult Q. alba and Q. rubra trees and other oaks as well we only focus on Q. alba and Q. rubra because of the limited geographic distribution and density of other species along this transect
Each acorn was inspected for exit holes, with each hole > 3 mm in diameter in the acorn pericarp assumed to be that of one Curculio larvae

Summary

Introduction

The oaks (genus Quercus), which includes ~350–500 species worldwide, are distributed widely across the globe from northwestern South America, through Central America, North America including Mexico, Europe, the northwestern edge of Africa, and much of eastern Asia [1,2,3,4]. Numerous studies have shown how various environmental factors influence larval infestation, survival and growth, and life history characteristics especially in Curculio species, clearly the most abundant and widespread insect predator of oak acorns Examples of such investigations include studies on the effects of annual acorn abundance and seed size of Curculio infestation (e.g., [4,5,6]), shifts in autumn seed drop of oaks in response to Curculio infestation [7,8], long-term patterns of Curculio infestation in oaks [9], the diversity of Curculionidae that occur in oaks [10] the effects of acorn satiation on life history traits and morphology of Curculio [11], the effects of both oak masting patterns and acorn size on patterns of satiation in Curculio [6,12,13,14], the effects of nitrogen deposition on patterns of weevil infestation and seed mortality [15], the impact of vertebrate seed predators on Curculio-infested acorns and weevil mortality (e.g., [8,16]), and the specific acorn characteristics (e.g., chemical gradients and germination strategies) tied to acorn tolerance of Curculio damage [4,17,18]. To ensure the most reliable measures of such latitudinal variation, we conducted our study over repeated years

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