Influence of abiotic factors on diapause termination and temperature requirements for postdiapause development in the European red mite, Panonychus ulmi (Acari: Tetranychidae)

The European red mite Panonychus ulmi (Koch) is widely distributed and it can severely affect pome fruit crops, particularly apple. Pest outbreaks are related to an overuse of non-selective pesticide treatments that lead to the development of resistance and the absence of natural enemies in the orchard. A key aspect to optimize the use of pesticide treatments in the context of IPM is to increase the knowledge on the biology and ecology of the pest to better predict population dynamics and outbreaks. For the European red mite, knowledge on the conditions that lead to diapause breaking by winter eggs is essential to model population dynamics. To increase this knowledge, winter eggs were collected during field surveys in northen Spain during three years and egg hatching was monitored under controlled temperature and photoperiod conditions in the laboratory. The "number of days exposed to cold temperatures" was the most significant factor that positively affected hatching of overwintering eggs. The time required for 50% of the egg population to hatch (T50%) was also negatively modulated by the duration of exposure to cold temperature. The temperature threshold for postdiapause eggs development collected from the field was estimated between 5 and 6 ºC in 2005 and 2007, respectively. Moreover, the degree-days required for post diapause development were estimated between 263.2 and 270.3, depending on the year of collection. Collectively, we provide additional information on the diapause termination and postdiapause development of the European red mite that may effectively contribute to optimize pest population models.

Effects of Ground Cover Management on Insect Predators and Pests in a Mediterranean Vineyard

Conservative techniques, such as ground cover management, could help promote viticulture sustainability, which is a goal of conservation biological control, by providing shelter and food sources for predatory insects. A field experiment was conducted in a Mediterranean vineyard to evaluate ground cover management impacts on predatory insect and potential grapevine pest abundance and diversity, both on the ground and in the grapevine canopy. Three different ground cover management techniques (tillage, spontaneous cover and flower-driven cover) were tested for two years (2016 and 2017). Overall, the ground cover management significantly affected the abundance of important epigeal predators, of which carabids, forficulids and staphylinids were the most captured. The carabid abundances under both the cover crop treatments were found to be approximately three times higher compared with that under the tillage treatment. In contrast, the canopy insect abundance in the vineyard was similar among the treatments for both the predators and the potential grapevine pest species. These results indicate that cover crop vegetation can be used in vineyards to enhance predatory insect abundance and may improve agroecosystem resilience.

Scavenging behavior and interspecific competition decrease offspring fitness of the entomopathogenic nematode Steinernema feltiae

Entomopathogenic nematodes (EPNs) are well-studied biocontrol agents of soil-dwelling arthropod pests. The insecticidal efficiency of EPNs is modulated by food web dynamics. EPNs can reproduce in freeze-killed insect larvae, even in competition with free-living bacterivorous nematodes (FLBNs) in the genus Oscheius. The objective of this study was to assess the efficiency of EPNs as scavengers when competing with free-living saprophagous nematodes and fungi, and to determine the possible impact on subsequent EPN offspring fitness. Live and freeze-killed larvae of Galleria mellonella were used to evaluate the reproduction rate and progeny fitness of two EPN species, Heterorhabditis bacteriophora and Steinernema feltiae, applied individually or combined with the FLBN species Oscheius onirici or Pristionchus maupasi, or Aspergillus flavus, an opportunistic saprophytic fungus. We hypothesized that (1) EPN scavenging behaviors previously observed (for H. megidis and S. kraussei) apply to other EPN species, (2) infective juveniles (IJs) emerging from freeze-killed larvae will display reduced pathogenicity and reproduction, and (3) fitness reduction will be amplified by exposure to other organisms competing for the resources. The reproduction rate of S. feltiae was lower in freeze-killed larvae than in larvae infected and killed by the nematode, whereas H. bacteriophora failed to reproduce as a scavenger. The S. feltiae F1 IJs that emerged from freeze-killed larvae exhibited lower pathogenicity rates than IJs resulting from entomopathogenic activity, and also lower reproductive rates if they experienced high FLBN competitive pressure during development. This study illustrates that scavenging is a suboptimal alternative pathway for EPNs, especially in the face of scavenger competition, even though it provides a means for some EPN species to complete their life-cycle.