Thermal tolerance of the rosy apple aphid Dysaphis plantaginea and its parasitoids: Effect of low temperatures on some fitness activities of Aphidius matricariae.

Understanding the thermal tolerance of insect herbivores and their natural enemies is crucial for biological control programs. The rosy apple aphid Dysaphis plantaginea is one of the most problematic pests of apple orchards, causing economic losses of up to 30% due to damage to fruits. Dysaphis plantaginea is highly adapted to low temperature, enabling it to appear early in the season. This study aimed at evaluating the critical thermal minimum of D. plantaginea and of two parasitoid species: Aphidius matricariae and Ephedrus cerasicola. For the generalist parasitoid A. matricariae we also evaluated the fitness traits of flight, walking, and oviposition, at four temperatures: 20, 15, 10 and 8 °C. We found that both males and females did not fly at the two lowest temperatures. Walking, parasitism rate and sex ratio (proportion of female progeny) were reduced at 8 °C. In addition, the parasitism rate was significantly lower at 8 and 10 °C compared to 15 and 20 °C. The progeny emerging from the oviposition experiment at 8 °C were significantly larger compared with other temperatures, possibly attributed to longer development time. The fact that the parasitoids were unable to fly at 8 and 10 °C, in combination with a more male-biased sex ratio, could reduce their efficiency at low temperature, even though they may still be able to walk and parasitize aphids.

Bottom-up regulation of a tritrophic system by Beet yellows virus infection: consequences for aphid-parasitoid foraging behaviour and development.

Effects of plants on herbivores can cascade up the food web and modulate the abundance of higher trophic levels. In agro-ecosystems, plant viruses can affect the interactions between crops, crop pests, and natural enemies. Little is known, however, about the effects of viruses on higher trophic levels, including parasitoids and their ability for pest regulation. We tested the hypothesis that a plant virus affects parasitoid foraging behaviour through cascading effects on higher trophic levels. We predicted that the semi-persistent Beet yellows virus (BYV) would influence plant (Beta vulgaris) quality, as well as aphid host (Aphis fabae) quality for a parasitoid Lysiphlebus fabarum. We determined amino acid and sugar content in healthy and infected plants (first trophic level), lipid content and body size of aphids (second trophic level) fed on both plants, as well as foraging behaviour and body size of parasitoids (third trophic level) that developed on aphids fed on both plants. Our results showed that virus infection increased sugars and decreased total amino acid content in B. vulgaris. We further observed an increase in aphid size without modification in host aphid quality (i.e., lipid content), and a slight effect on parasitoid behaviour through an increased number of antennal contacts with host aphids. Although the BYV virus clearly affected the first two trophic levels, it did not affect development or emergence of parasitoids. As the parasitoid L. fabarum does not seem to be affected by the virus, we discuss the possibility of using it for the development of targeted biological control against aphids.

Ecology and biology of the parasitoid Trechnites insidiosus and its potential for biological control of pear psyllids.

Pear cultivation accounts for a large proportion of worldwide orchards, but its sustainability is controversial because it relies on intensive use of pesticides. It is therefore crucial and timely to find alternative methods to chemical control in pear orchards. The psyllids Cacopsylla pyri and Cacopsylla pyricola are the most important pests of pear trees in Europe and North America, respectively, because they infest all commercial varieties, causing damage directly through sap consumption or indirectly through the spread of diseases. A set of natural enemies exists, ranging from generalist predators to specialist parasitoids. Trechnites insidiosus (Crawford) is undoubtedly the most abundant specialist parasitoid of psyllids. In our literature review, we highlight the potential of this encyrtid species as a biological control agent of psyllid pests by first reviewing its biology and ecology, and then considering its potential at regulating psyllids. We show that the parasitoid can express fairly high parasitism rates in orchards, and almost perfectly matches the phenology of its host and is present early in the host infestation season, which is an advantage for controlling immature stages of psyllids. We propose new research directions and innovative approaches that would improve the use of T. insidiosus in integrated pest management strategies in the future, regarding both augmentative and conservation biocontrol. We conclude that T. insidiosus has many advantages and should be included as part of integrated biological control strategies of pear psyllids, along with predators, in-field habitat conservation, and the rational use of compatible chemicals. © 2021 Society of Chemical Industry.