Density-Dependent Benefits in Ant-Hemipteran Mutualism? The Case of the Ghost Ant Tapinoma melanocephalum (Hymenoptera: Formicidae) and the Invasive Mealybug Phenacoccus solenopsis (Hemiptera: Pseudococcidae)

Abstract

Although density-dependent benefits to hemipterans from ant tending have been measured many times, few studies have focused on integrated effects such as interactions between ant tending, natural enemy density, and hemipteran density. In this study, we tested whether the invasive mealybug Phenacoccus solenopsis is affected by tending by ghost ants (Tapinoma melanocephalum), the presence of parasitoids, mealybug density, parasitoid density and interactions among these factors. Our results showed that mealybug colony growth rate and percentage parasitism were significantly affected by ant tending, parasitoid presence, and initial mealybug density separately. However, there were no interactions among the independent factors. There were also no significant interactions between ant tending and parasitoid density on either mealybug colony growth rate or percentage parasitism. Mealybug colony growth rate showed a negative linear relationship with initial mealybug density but a positive linear relationship with the level of ant tending. These results suggest that benefits to mealybugs are density-independent and are affected by ant tending level.

Temperature warming strengthens the mutualism between ghost ants and invasive mealybugs

“…Although both the colony growth and parasitism of mealybugs decreased under extreme temperature (32 °C), ant tending level and aggression were greatly enhanced. It has been demonstrated that there is a positive linear relationship between ant tending level and mealybug colony growth rate 35 , which suggests that temperature warming could promote mealybug colony growth directly or indirectly. Thus, the net effect of temperature warming is to increase mealybug colony by benefiting ghost ant-mealybug mutualism.…”

“…Moreover, ant foraging frequency mediates the tending level and protection ability for hemipterans 32 , 33 . Benefits to hemipterans are positively and linearly related to ant tending level 26 , 34 , 35 . Aphids directly respond to elevated temperature with decreased developmental time and reduced adult and progeny weight 36 , 37 .…”

“…This mutual relationship is stable when the trade-off between the cost and benefit is in balance 47 . Currently, many studies have documented that these steady interactions are mediated by numerous biotic factors 23 , 34 , 35 , 48 – 53 . Both mealybug Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae) and ghost ant Tapinoma melanocephalum (Fabricius) (Hymenoptera: Formicidae) are important invasive species in China, which have established a close mutualistic relationship in the ecosystem 54 .…”

Does the host plant affect the benefits from mutualisms?The invasive mealybug and ghost ant association

“…Those results may suggest that the ant tending level is mediated by host plants. It is clear that the intensity of mutualisms and the ant tending level can be affected by the temporal factor, age-specific, and the density of the hemipterans (Cushman & Whitham, 1989;Breton & Addicott, 1992;Itioka & Inoue, 1996;Morales, 2000;Zhou et al, 2015a). In contrast, few studies of ant-hemipteran mutualisms reported the patterns of host plants-dependent effects.…”

Invasion biology of the cotton mealybug, Phenacoccus solenopsis Tinsley: Current knowledge and future directions

“…However, mutualism is seemingly independent of the density of the animal species involved. One study showed that the benefit provided by T. melanocephalum to mealybugs was not significantly affected by the density of either mealybugs or the parasitoid A. bambawalei (Zhou et al 2015c).…”