Abstract
The lower and upper thermal activity thresholds of adult and larval Balaustium hernandezi von Heyden (Acari: Erythraeidae) are compared with those of its prey Tetranychus urticae Koch (Acari: Tetranychidae). Adult female B. hernandezi retain ambulatory function (CTmin) and movement of appendages (chill coma) at significantly lower temperatures (5.9 and −2.1 °C, respectively) than those of larval B. hernandezi (8.1 and −1.7 °C) and T. urticae (10.6 and 10.3 °C). There is no significant difference between the temperature at which adult and larval B. hernandezi and T. urticae cease walking as the temperature is raised (CTmax) (46.7, 46.3 and 47.3 °C, respectively). However, both life stages of B. hernandezi cease movement (heat coma) below the upper locomotory limits of T. urticae (46.8, 46.7 and 48.7 °C, respectively). Adult B. hernandezi have significantly faster walking speeds than larvae and T. urticae across a range of temperatures. The lower thermal activity threshold data indicate that B. hernandezi would make an effective biological control agent in temperate climates; however, the extent of the low temperature tolerances of the species suggests the potential to establish in a northern European climate.
Highlights
Augmentative biological control comprises the application of a natural enemy in areas where abiotic factors prevent prolonged survival and reproduction, and is considered to be an environmentally safe and cost effective method of crop pest management (van Lenteren & Bueno, 2003; van Lenteren, 2011)
There was a significant difference between the mean temperatures at which B. hernandezi adults (P < 0.001; F1,58 = 954.25) and larvae (P < 0.001; F1,58 = 214.0) ceased ambulation and twitching of appendages; there was no significant difference between the temperatures at which T. urticae demonstrated these behaviours (P = 0.610; F1,58 = 0.26)
Invertebrate behaviour is dictated by temperature and, as such, the study of thermal thresholds has particular importance with respect to the assessment of the suitability of a species for biological control
Summary
Augmentative biological control comprises the application of a natural enemy in areas where abiotic factors prevent prolonged survival and reproduction, and is considered to be an environmentally safe and cost effective method of crop pest management (van Lenteren & Bueno, 2003; van Lenteren, 2011). There is no existing Europe-wide legislation to regulate the release of invertebrate biocontrol agents, resulting in a difference in the licensing process in different European countries, a number of countries, including the U.K. and the Netherlands, operate under a more standardized process (Bale, 2011). To comply with these guidelines, any potential biological control agent must be assessed using appropriate methods to determine the establishment potential and host range Previous investigations report concentrating on the low winter temperatures preventing the establishment of non-native natural enemies that escape from glasshouses and other protected environments (Tullett et al, 2004; Hatherly et al, 2005; Hughes et al, 2009; Bale, 2011)
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