Tetranychus urticae, Koch, 1836

Al-Azzazy, Mahmoud M., Alsohim, Abdullah S. & Yoder, Carl E., 2020, Biological effects of three bacterial species on Tetranychus urticae (Acari: Tetranychidae) infesting eggplant under laboratory and greenhouse conditions, Acarologia 60 (3), pp. 587-594 : 591-592

Symptoms of T. urticae with a bacterial infection

Bacterial pathogens invade their hosts mostly through the mouth and alimentary canal. Less often, they enter through peritremes and wounds in the integument ( Poinar and Poinar, 1998). Bacterial infections may be classified as toxaemia, when bacteria are confined in the alimentary canal where they produce toxins, bacteremia, when bacteria multiply in the hemolymph of the mite without producing toxins (apparently unaffected by the mite immune system), or septicaemia, when bacteria multiply in the hemocoel, producing toxins and killing the mite ( Tanada and Kaya, 1993) . In the present study, many of these factors might have contributed to the mortality of the two-spotted spider mite. Diagnostic features considered as general characteristics of bacterial infection were recorded in the current study: distinct color changes (dark brown color with a black tinge), degeneration of internal tissues, discontinuation of

Treatment Days after treatment 1 2 3 4 5 6 7 P value Acinetobacter sp. 29.89 Aa 45.95 Ab 77.29 Ac 75.19 Ac 74.99 Ac 74.82 Ac 73.80 Ac 0.0088 2.237 ×10 8 cfu/ml B. subtilis 10.28 Ba 24.31 Bb 41.06 Bc 55.48 Bd 61.36 Bd 64.77 Bd 67.11 Bd 0.0071 2.470 ×10 8 cfu/ml B. qassimus 9.14 Ca 23.55 Cb 40.25 Cc 54.97 Cd 60.08 Cd 63.07 Cd 65.19 Cd 0.009 3.320 ×10 8 cfu/ml P value 0.0048 0.0066 0.0079 0.0094 0.0041 0.0056 0.0073 The capital letter denotes significant differences within the same column and small letter denotes the significant differences within the same row at P<0.01.

feeding, inability to move, weakening of the outer skin, females failing to oviposit, excretion of diarrhoea-like faeces, occasionally causing mites to become glued to the substrate, vomiting and cadavers becoming black due to the bacterial infection ( Figure 1 ).In another study ( Wilson et al., 2002) reported that bacterial hemolysins are exotoxins that attack blood cell membranes and cause cell rupture and body swelling. These hemolysins may also be involved in the pathogenicity of the three bacterial species on T. urticae , especially given the rapid mortality observed.

We can hypothesize that Acinetobacter sp. was found to be a better bacterial agent under greenhouse and lab experiments, because of its higher colonizing capacity in small-bodied mites by providing very strong adhesion to the cuticle ( Van der Geest et al., 2000). Future studies would be needed to understand interactions between mites and these bacterial pathogens.

Figures

Figure 1 Pictures of dead mite individuals after spray with the pathogenic bacteria: A – Acinetobacter sp.; B –B. subtilis and C –B. qassimus