Elevated CO2 Levels Impact Fitness Traits of Vine Mealybug Planococcus ficus Signoret, but Not Its Parasitoid Leptomastix dactylopii Howard

Abstract

Carbon dioxide (CO 2 ) is one of the primary factors driving climate change impacts on plants, pests, and natural enemies. The present study reports the effects of different atmospheric CO 2 concentrations on the vine mealybug Planococcus ficus (Signoret) and its parasitoid wasp Leptomastix dactylopii (Howard). We investigated the life-history parameters of both species on grapevine Vitis vinifera (L.) plants grown under elevated (eCO 2 ) and ambient (aCO 2 ) CO 2 levels in a greenhouse and in a vineyard free-air carbon dioxide enrichment (FACE) facility. The greenhouse experiments with an eCO 2 level of around 800 ppm showed a significant increase in survival rates, a strong trend towards declining body size, and an increasing fecundity of female mealybugs, while fertility and development time did not change. However, none of these parameters were altered by different CO 2 concentrations in the VineyardFACE facility (eCO 2 level around 450 ppm). On the other hand, the parasitism success, development time and sex ratio of L. dactylopii, reared on P. ficus under eCO 2 or aCO 2 , varied neither in the greenhouse nor in the FACE facility. These results suggest that future CO 2 levels might cause small-scale changes in vine mealybug fitness; however, this is not necessarily reflected by parasitoid performance.Agronomy 2019, 9, 326 2 of 12 while phloem-feeders seem to be less affected. Several studies report an improved aphid fitness under elevated CO 2 (eCO 2 ) [3,8], although the mechanisms behind this are not yet fully understood. While aphids are a primary pest in many agricultural and horticultural systems, mealybugs, such as the vine mealybug Planococcus ficus Signoret (Hemiptera: Pseudococcidae), are a much bigger concern in grapevine production.Planococcus ficus is an invasive phloem-feeding insect from the Mediterranean area, which has become a serious invasive pest in many grape-growing regions worldwide [9,10]. Mealybugs affect grapevines both directly and indirectly. By feeding on the phloem sap of all plant organs, mealybugs weaken the plants' vigour. Furthermore, the excreted honeydew promotes the growth of sooty mould on leaves and fruits, reducing photosynthesis, grape marketability and wine quality [9,11,12]. Planococcus ficus is also known to transmit grapevine leafroll-associated virus (GLRaV) and other diseases, which reduce the crop yield and wine quality [13,14]. Mealybug control was based on repeated applications of broad-spectrum insecticides, although with limited success, as mealybugs feed not only on the canopy, but also under the bark and in the root area [15], where they are inaccessible to contact-active pesticides. Additionally, the reiterated use of broad-spectrum insecticides is associated with negative effects on non-target organisms, including biological control agents, and the risk of future pesticide resistance [10,16,17]. Therefore, alternative methods for mealybug control include employing new pesticides, pheromone-based mating disruption, and biological control [18][19][20][21][...

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