Department of Entomology and MOA Key Lab of Pest Monitoring and Green Management, College of Plant Protection, China Agricultural University, Beijing, China.
PLoS One. 2018 Nov 28;13(11):e0206816. doi: 10.1371/journal.pone.0206816. eCollection 2018.
Insects such as locusts and grasshoppers can reduce the effectiveness of pathogens and parasites by adopting different defense strategies. We investigated the behavioral thermopreference of Locusta migratoria manilensis (Meyen) (Orthoptera: Acrididae) induced by the fungus Beauveria bassiana, and the impact this behavior had on the fungal mycosis under laboratory conditions. By basking in higher temperature locations, infected nymphs elevated their thoracic temperature to 30-32.6 °C, which is higher than the optimum temperature (25°C) for B. bassiana conidial germination and hyphal development. A minimum thermoregulation period of 3 h/day increased survival of infected locusts by 43.34%. The therapeutic effect decreased when thermoregulation was delayed after initial infection. The fungus grew and overcame the locusts as soon as the thermoregulation was interrupted, indicating that thermoregulation helped the insects to cope with infection but did not completely rid them of the fungus. A significant enhancement in the number of haemocytes was observed in infected thermoregulating locusts, reaching levels that were even higher than those observed in the controls. In contrast, haemocyte concentration was severely reduced in infected insects that did not thermoregulate. In infected non-thermoregulating locusts, the reduction in haemocyte number was accompanied by an increase in fungal blastospore concentration that was obvious in the haemolymph by day four. In contrast, no circulating blastospores were found in the haemolymph of infected thermoregulating locusts three days post-inoculation. We also examined the phagocytic activity of infected insects in vivo by using fluorescein isothiocyanate (FITC)-labelled silica beads. The proportion of beads that was engulfed by haemocytes in infected, thermoregulating insects was similar to that in the controls throughout the experiment, whereas the rate of phagocytosis in infected, non-thermoregulating insects progressively decreased after infection. These findings demonstrated that behavioural thermoregulation can adversely affect B. bassiana mycosis in infected L. migratoria manilensis, thereby limiting the development of lethal entomopathogenic fungi in locusts. This is apparently accomplished through an increase in the levels of haemocytes, leading to greater phagocytic activity under certain environmental conditions.
昆虫如蝗虫和蚱蜢可以通过采用不同的防御策略来降低病原体和寄生虫的有效性。我们研究了被真菌绿僵菌诱导的东亚飞蝗（Locusta migratoria manilensis（Meyen））（直翅目：蝗科）的行为热偏好，以及这种行为对实验室条件下真菌病的影响。受感染的若虫通过在较高温度的地方晒热，将其胸部温度升高到 30-32.6°C，这高于绿僵菌分生孢子萌发和菌丝生长的最佳温度（25°C）。每天至少 3 小时的体温调节期可使受感染的蝗虫的存活率提高 43.34%。感染后延迟体温调节会降低治疗效果。一旦中断体温调节，真菌就会生长并战胜蝗虫，表明体温调节有助于昆虫应对感染，但并不能完全清除真菌。受感染的体温调节蝗虫的血细胞数量显著增加，甚至高于对照组。相比之下，未进行体温调节的受感染昆虫的血细胞浓度严重降低。在未进行体温调节的感染昆虫中，血细胞数量的减少伴随着真菌芽生孢子浓度的增加，在第四天的血淋巴中明显增加。相比之下，在感染后三天的受感染体温调节蝗虫的血淋巴中未发现循环芽生孢子。我们还通过使用异硫氰酸荧光素（FITC）标记的硅珠在体内检查了感染昆虫的吞噬活性。在整个实验过程中，受感染、体温调节的昆虫中被血细胞吞噬的珠粒比例与对照组相似，而受感染、非体温调节的昆虫的吞噬率在感染后逐渐下降。这些发现表明，行为性体温调节可以对感染的东亚飞蝗中的绿僵菌真菌病产生不利影响，从而限制致命的昆虫病原真菌在蝗虫中的发展。这显然是通过增加血细胞水平来实现的，从而在某些环境条件下导致更大的吞噬活性。
