Ant–hemipteran association decreases parasitism of Phenacoccus solenopsis by endoparasitoid Aenasius bambawalei

1. Mutualism between ants and honeydew-excreting hemipterans is ubiquitous in the ecosystem. It is widely accepted that ant tending facilitates the colony growth of hemipterans by protecting them from predators and parasitoids. However, few studies have explored how ant tending helps defend against natural enemies. 2. Ghost ant Tapinoma melanocephalum and the invasive mealybug Phenacoccus solenopsis have a close mutual relationship. Previous studies have shown that ghost ant tending can definitely reduce parasitism and visit frequency of Aenasius bambawalei, the dominant endoparasitoid of P. solenopsis. However, the ghost ant workers seldom attack the parasitoids. It is still unclear how the ghost ant adversely affects parasitoids. This study explored the mechanism underlying the impacts of ants on natural enemies of the mealybugs. 3. Honeydew produced by P. solenopsis was an attractant to A. bambawalei. Parasitoids exhibited less searching activity, shorter longevity and lower parasitism when supplied with less honeydew. Aenasius bambawalei showed significant avoidance of pygidial gland secretions and visual cues of ghost ants. Parasitism in plants treated with 6-methyl-5-hepten-2-one, actinidine, and gland extracts was significantly lower than that in plants treated only with solvents (paraffin oil or double-distilled water). 4. It is concluded that honeydew consumption by ghost ants could negatively influence the performance of parasitoids. The pygidial gland secretions and visual cues of ghost ants also significantly inhibit the parasitism. These results may contribute to a better understanding of the regulation mechanism in ant–hemipteran–enemy interactions.     

Social and psychological factors of the suicidal tendencies of Chinese medical students

Background

Over the past few decades, concern about suicide by college students has been on the rise worldwide, in general and in China particularly. The main objective of this study is to investigate the effects of social and psychological factors on the suicidal tendencies of Chinese medical students.

Findings

Of the 540 students surveyed, 48 had a suicidal tendency to some extent. The highest rate of suicide was observed for fourth-year students, followed by the fifth-year, first-year, third-year, and second-year students. Female students and students not satisfied with their major had a higher rate of suicidal tendency. However, mature coping strategies had a protective effect on suicide. The stepwise regression analysis shows that academic burden, grade, and introversion/extraversion are the most significant risk factors for the suicidal tendency of Chinese medical students.

Conclusion

Suicide is affected by demographic risk factors as well as psychological factors. Our results lend support to a multi-factorial approach to the understanding and prevention of suicide by college students.

     

Interspecific competition between the red imported fire ant,Solenopsis invicta Buren and ghost ant,Tapinoma melanocephalum Fabricius for honeydew resources produced by an invasive mealybug,Phenacoccus solenopsis Tinsiley

In natural as in agricultural ecosystems, interactions between ants and honeydew-producing hemipterans are commonly observed. Mutualisms between invasive ants and hemipterans have been extensively studied in recent years. However, native ant species can equally exploit the honeydew excreted by hemipterans, and establish close relationships with them. Up till present, little is known about the competition between exotic ants (such as Solenopsis invicta) and its co-occurring species (e.g., Tapinoma melanocephalum) for this food resource. In this study, we compared the competitive ability of the invasive ant S. invicta and its co-occurring species T. melanocephalum in the laboratory. We also determined whether the two ant species could coexist and share honeydew resource. Our results indicate that the foraging activity of T. melanocephalum was restrained by S. invicta. Mortality of S. invicta and T. melanocephalum was significantly higher in T. melanocephalum colony case than that in other cases. The invasive ability between the two ant species was significantly different. These results suggest that S. invicta suppresses exploitation of honeydew-producing hemipterans by native ants and occupies most of honeydew resource. S. invicta could not completely drive T. melanocephalum out of honeydew competition, with small numbers of T. melanocephalum workers coexisting and sharing the honeydew with S. invicta. This finding permits a better understanding of the invasion success of S. invicta, and its ability to occupy new habitats.     

Effects of the invasive plant Eupatorium adenophorum on the exotic mealybug Phenacoccus solenopsis (Hemiptera: Pseudococcidae) and their natural enemies

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