Effect of Drought on Outbreaks of Major Forest Pests, Pine Caterpillars (Dendrolimus spp.), in Shandong Province, China

Jiquan Zhang,Li Na,Yongbin Bao,Fei Wang,Yunchi Han,Siqin Tong,Aru Han,Yuhai Bao,Qiumei Zhang

doi:10.3390/f10030264

Abstract

As the main defoliators of coniferous forests in Shandong Province, China, pine caterpillars (including Dendrolimus suffuscus suffuscus Lajonquiere, D. spectabilis Butler, and D. tabulaeformis Tsai et Liu) have caused substantial forest damage, adverse economic impacts, and losses of ecosystem resources. Therefore, elucidating the effects of drought on the outbreak of these pests is important for promoting forestry production and ecological reconstruction. Accordingly, the aim of the present study was to analyse the spatiotemporal variation of drought in Shandong Province, using the Standard Precipitation Index, and to investigate the impact of drought on the outbreak of pine caterpillar infestations. Future trends in drought and pine caterpillar populations were then estimated using the Hurst exponent. The results showed that: (1) Drought decreased gradually and showed a wetting trend from 1981 to 2012, with frequency decreasing on a decadal scale as follows: 1980s > 1990s > 2000s > 2010s; (2) The total area of pine caterpillar occurrence decreased strongly from 1992 to 2012; (3) Long-term or prolonged drought had a greater positive impact on pine caterpillar outbreak than short-term drought; (4) In the future, a greater portion of the province’s area will experience increased wetting conditions (57%) than increased drought (43%), and the area of pine caterpillar outbreak is estimated to decrease overall. These findings help elucidate the relationship between drought and pine caterpillar outbreak in Shandong Province and, hence, provide a basis for developing preventive measures and plans.

Highlights

Insects play important roles in the maintenance of ecosystem structure, function, and biodiversity, but they have the potential to threaten natural, biological, and social environments and even to cause disasters [1,2]
A significant period of drought was detected during the 1980s and 1999–2003, whereas major wet episodes occurred during the mid-1990s and after 2003
The results suggest that Standardized Precipitation Index (SPI)-12 intuitively reflects annual variations in drought and it is used in the following study

Summary

Introduction

Insects play important roles in the maintenance of ecosystem structure, function, and biodiversity, but they have the potential to threaten natural, biological, and social environments and even to cause disasters [1,2]. Outbreaks of insect pests are affected by its own inherited characteristics but are influenced by: (1) host tree abundance, (2) high insect population density, and (3) adaptive. Climate and weather can influence insect outbreaks both directly or indirectly, by affecting insect growth, reproduction, spread, and hosts [4]. Increasing drought frequency has been identified as an important predisposing factor that can trigger insect outbreaks, directly by affecting insect population dynamics and indirectly by altering host plant growth and defence [6,7]. Extensive research has demonstrated that severe or prolonged drought has adverse effects on tree growth and survival and that it can trigger more frequent or severe outbreaks of forest pests [8]

Objectives

Methods

Results

Discussion

Conclusion