Neoseiulus californicus (Acari: Phytoseiidae) shows good predation potential when reared on an artificial diet supplemented with Tetranychus cinnabarinus

To evaluate the predation potential of Neoseiulus californicus (McGregor) reared on an artificial diet as a biological control agent for Tetranychus cinnabarinus (Boisduval), life table and functional response studies were performed. To identify alternative food sources for rearing N. californicus, we compared the nutritional values of the basal diet (composed of sucrose, yeast extract, honey, tryptone and egg yolk), meridic diet (add T. cinnabarinus on the basis of basal diet) and control (T. cinnabarinus). Further, the predation ability of N. californicus continuously reared for ten consecutive generations on a meridic diet to control T. cinnabarinus was assessed. The results showed that N. californicus fed the basal and meridic diets successfully completed development from eggs to adults, but they did not oviposit when fed the basal diet. The high fecundity (41.00 eggs per female) and intrinsic rate of increase (0.2357 d-1) recorded in the meridic diet group suggests that it is a suitable diet for N. californicus rearing. Additionally, a functional response (type II) was observed in N. californicus reared on the meridic diet. We found that when the predator was reared on the meridic diet, the estimated maximum attack rate (T/Th) associated with larvae was 58.67, which was only 13.94% lower than the control (68.17). The 10th generation of N. californicus did not lose the ability to capture and kill T. cinnabarinus when fed on meridic diet. In conclusion, N. californicus reared on the meridic diet containing T. cinnabarinus showed good predation ability; therefore, this diet may be beneficial for the mass production of N. californicus.

Influence of irrigation regimes on yield, pomological parameters and population development of Tetranychus cinnabarinus Boisd. (Acari: Tetranychidae) in strawberry

In this study, the effect of full (IR100), 50% (IR50), 75% (IR75) and 125% (IR125) irrigation levels on population development of the carmine spider mite (CSM) as well as on yield and some pomological properties of ‘Fortuna’ strawberry cultivar grown in high tunnels were evaluated in two consecutive growing seasons (2016–2017 and 2017–2018). The numbers of CSM were significantly lower on strawberry leaves which were irrigated by IR50 and IR75 in both growing seasons. Full (IR100) and highest (IR125) irrigation levels were the most favorable for the development of CSM populations. On the other hand, in the CSM thriving period (2017), the fruit weight was generally high in the plots with the highest irrigation (IR125) level. Although there was no interaction with the CSM population, fruit acidity (%) increased in the IR100 and IR125 irrigation levels, possibly due to stress in plants, when CSM population was highest (in March). In the absence of CSM, fruit acidity was significantly high in the plots where water stress was experienced. While no significant interaction was found between the pomological characters and the CSM population, the mites affected the yield significantly in that plants were more productive under IR 75 even when there was a CSM population. This study suggests that the application of IR75 level in Fortuna strawberry is related to lower CSM population growth and significantly higher yields.

Molecular Characterization of Chitin Synthase Gene in Tetranychus cinnabarinus (Boisduval) and Its Response to Sublethal Concentrations of an Insecticide

The carmine spider mite, Tetranychus cinnabarinus (Boisduval), is one of the most important acarine pest species. At present, its control remains primarily dependent on using various chemical insecticides/acaricides in agricultural crops worldwide. To clarify the mechanism whereby T. cinnabarinus responds to insecticide exposure, we identified the chitin synthase 1 gene (TcCHS1) and then explored the gene expression levels of TcCHS1 at different developmental stages of T. cinnabarinus. We also investigated the effects of sublethal concentrations of diflubenzuron on the toxicities and survivals of T. cinnabarinus eggs and larvae as well as TcCHS1 expression levels. The full-length cDNA sequence contains an open reading frame (ORF) of 4881 nucleotides that encoded for a 1474 amino acid residues protein. The predicted TcCHS1 protein had a molecular mass of 168.35 kDa and an isoelectric point of 6.26, and its amino acid sequence contained all the signature motifs (EDR, QRRRW and TWGTR) of chitin synthases. The results of phylogenetic analyses demonstrated that the putative CHS1 amino acid sequence of T. cinnabarinus revealed high similarities with chitin synthases in other insects and mites. Additionally, at the molecular level, transcriptional analysis by real-time quantitative PCR in different developmental stages of T. cinnabarinus revealed that TcCHS1 mRNA was expressed in all stages, and highest in eggs and female adults, but lowest in deutonymphs. Furthermore, the results of toxicity bioassays indicated that diflubenzuron treatment resulted in high mortality rates in eggs and larvae of T. cinnabarinus. The mRNA expression levels of TcCHS1 from the eggs and larvae of T. cinnabarinus were up-regulated in response to sublethal concentrations of diflubenzuron exposures. Together, all these results demonstrate that diflubenzuron has ovicidal and larvicidal effects and TcCHS1 may play an important role in the growth and development of T. cinnabarinus and may disrupt the chitin biosynthesis, thereby controlling T. cinnabarinus populations.