Animals use signals to coordinate a wide range of behaviors, from feeding offspring to predator avoidance. This poses an evolutionary problem, because individuals could potentially signal dishonestly to coerce others into behaving in ways that benefit the signaler. Theory suggests that honest signaling is favored when individuals share a common interest and signals carry reliable information. Here, we exploit the opportunities offered by bacterial signaling to test these predictions with an experimental evolution approach. We show that: (1) reduced relatedness leads to the relative breakdown of signaling, (2) signaling breaks down by the invasion of mutants that show both reduced signaling and reduced response to signal, (3) the genetic route to signaling breakdown is variable, and (4) the addition of artificial signal, to interfere with signal information, also leads to reduced signaling. Our results provide clear support for signaling theory, but we did not find evidence for previously predicted coercion at intermediate relatedness, suggesting that mechanistic details can alter the qualitative nature of specific predictions. Furthermore, populations evolved under low relatedness caused less mortality to insect hosts, showing how signal evolution in bacterial pathogens can drive the evolution of virulence in the opposite direction to that often predicted by theory.
Due to problems with chemical control, there is increasing interest in the use of microsporidia for control of lepidopteran pests. However, there have been few studies to evaluate the susceptibility of exotic species to microsporidia from indigenous Lepidoptera.
Biological control using pathogenic microsporidia could be an alternative to chemical control of the diamondback moth (DBM) Plutella xylostella (Lepidoptera: Plutellidae). The microsporidium Nosema bombycis (NB) is one of the numerous pathogens that can be used in the Integrated Pest Management (IPM) of DBM. However, its pathogenicity or effectiveness can be influenced by various factors, particularly temperature. This study was therefore conducted to investigate the effect of temperature on NB infection of DBM larvae. Second-instar larvae at different doses (spore concentration: 0, 1×10²,1×10³,1×10⁴, and 1×10⁵) at 15°, 20°, 25°, 30° and 35°C and a relative humidity(RH) of 65% and light dark cycle (L:D) of 12∶12. Larval mortality was recorded at 24 h intervals until the larvae had either died or pupated. The results showed that the spore concentration had a significant negative effect on larval survival at all temperatures, although this effect was more pronounced (92%) at 35°C compared with that at 20 and 30°C (≃50%) and 25°C (26%). Histological observations showed that Nosema preferentially infected the adipose tissue and epithelial cells of the midgut, resulting in marked vacuolization of the cytoplasm. These findings suggest that Nosema damaged the midgut epithelial cells. Our results suggest that Nosema had a direct adverse effect on DBM, and could be utilized as an important biopesticide alternative to chemical insecticides in IPM.
Species-specific primers for Zoophthora radicans and Pandora bluckii were developed. To achieve this, partial sequences of DNA that encode for rRNA, more specifically, the ITS region (rDNA-ITS) were obtained from different isolates and analysed. Seven Z. radicans isolates (four from P. xylostella, and three from other lepidopteran hosts) and one P. blunckii isolate (from P. xylostella) were used. These isolates were selected based on PCR-RFLP patterns obtained from 22 isolates of P. blunckii and 39 isolates of Z. radicans. All P. blunckii isolates were from the same host (P. xylostella); 20 isolates were from Mexico, one from the Philippines, and one from Germany. The Z. radicans isolates were more diverse in geographical origin (Mexico, Kenya, Japan, New Zealand, Australia, Taiwan, Philippines, Malaysia, Uruguay, France, USA, Poland, Indonesia, Switzerland, Israel, China, and Denmark) and host origin (Lepidoptera, Hemiptera, Hymentoptera, and Diptera). Using conventional PCR, each pair of species-specific primers successfully detected each species of fungus from DNA extracted from infected host larvae either single- or dual-inoculated with both fungal species. The PCR-RFLP analysis also showed that Z. radicans was genetically more diverse than P. blunckii, although only a limited number of P. blunckii isolates from one country were considered. There was no direct relationship between genetic diversity and host or geographical origin. The relationship between genetic variation within both fungal species and host specificity or ecological adaptation is discussed.
Patterns of mtDNA variation within a species reflect long-term population structure, but may also be influenced by maternally inherited endosymbionts, such as Wolbachia. These bacteria often alter host reproductive biology and can drive particular mtDNA haplotypes through populations. We investigated the impacts of Wolbachia infection and geography on mtDNA variation in the diamondback moth, a major global pest whose geographic distribution reflects both natural processes and transport via human agricultural activities.