Abstract
We studied the effect of three Pandora neoaphidis isolates from one Sitobion avenae population, three temperatures, and two aphid species namely S. avenae and Rhopalosiphum padi on (i) aphid mortality, (ii) time needed to kill aphids, and (iii) aphid average daily and lifetime fecundity. A total of 38% of S. avenae and 7% of R. padi died and supported fungus sporulation. S. avenae was killed 30% faster than R. padi . Average daily fecundity was negatively affected only in S. avenae inoculated with, but not killed by, P. neoaphidis . Nevertheless, lifetime fecundity of both aphid species inoculated and sporulating with P. neoaphidis was halved compared to lifetime fecundity of surviving aphids in the control. Increased temperature resulted in higher mortality rates but did not consistently affect lethal time or fecundity. Results suggest that (i) temperature effects on virulence differ between isolates, even when obtained within the same host population, and (ii) even though an isolate does not kill a host it may reduce its fecundity. Our findings are important for the understanding of P. neoaphidis epizootiology and for use in pest-natural enemy modelling. • Pandora neoaphidis from Sitobion avenae kills both S. avenae and Rhopalosiphum padi. • P. neoaphidis isolates tested were much more virulent to S. avenae than R. padi. • Temperature influences virulence of isolates from one population differently. • Temperature influences mortality, lethal time and fecundity differently. • S. avenae surviving fungal infection had reduced average daily fecundity.
Highlights
IntroductionPlant pests (weeds, pathogens, arthropods) and their natural enemies (microorganisms, predators and parasitoids) interact with each other directly and indirectly through the plant
Plant pests and their natural enemies interact with each other directly and indirectly through the plant
Rhopalosiphum padi There was no significant difference between P. neoaphidis isolates in sporulation of R. padi cadavers (Chi2 1⁄4 1.459, df 1⁄4 2, p 1⁄4 0.482) (Fig. 1A)
Summary
Plant pests (weeds, pathogens, arthropods) and their natural enemies (microorganisms, predators and parasitoids) interact with each other directly and indirectly through the plant. An example of nontarget effects of plant protection measures are insecticides killing predators and parasitoids, leading to a resurgence of secondary pests (Fernandes et al, 2010) This can work across pest categories, as observed when fungicides used against plant pathogens kill beneficial fungi (Klingen and Westrum, 2007), leading to higher levels of pest arthropods and subsequent pesticide use. In USA, farmers withhold insecticide application for the cotton aphid during epizootics of the aphid-killing fungus Neozygites fresenii to enhance control of the aphid population by this beneficial fungus (Hollingsworth et al, 1995). More strategies such as this are needed. To build pest-natural enemy models to serve as a basis for such strategies, detailed studies on biotic and abiotic factors affecting these interactions are needed
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