Implications of Climate Change for Toxoptera citricida (Kirkaldy), a Disease Vector of Citrus in Florida

Abstract

Increasing temperatures, elevated CO2 levels, and changes in rainfall patterns are predicted to impact plants and insects, both harmful and beneficial. Toxoptera citricida Kirkaldy (Homoptera: Aphididae), commonly known as the brown citrus aphid (BrCA), is a cosmopolitan pest of citrus and a highly efficient vector of citrus tristeza virus (CTV). Both the pest and the disease pose a serious threat to citrus production in Florida. Temperature is the most important abiotic factor impacting the biology of BrCA and the growth of new citrus shoots on which the aphid depends for development and reproduction. Climate in most parts of the state is humid subtropical, characterized by mild to cool, relatively dry winters and autumns and hot, wet springs and summers. Cool winters, freezes and hot summers limit the aphid’s ability to survive and reproduce, leaving spring as the optimal season for population growth. Mature citrus trees go through a period of winter dormancy followed by a surge of growth in spring and periods of sporadic growth in summer and fall. Any significant rise in average winter temperatures will reduce the severity and duration of cool winter weather and may trigger earlier shoot growth by citrus trees. This would improve aphid survival in winter, provide a food bridge between fall and spring populations, and possibly lead to earlier recruitment of natural enemies, particularly predators. Summers, on the other hand, if warmer and more prolonged would probably be less tolerable for the BrCA and its natural enemies. However, adaptation to environmental change is possible and low aphid populations are observed in the field at temperatures above the upper threshold for development determined under laboratory conditions. The negative impact of rising temperatures on BrCA populations may be more pronounced in the south than elsewhere due to the relatively higher temperatures there, with more beneficial effects evident in the north.