Redescription of three species of Aponychus from China with ontogenetic development and morphological variations of A. corpuzae (Acariformes: Tetranychidae).

Ontogenetic development of leg chaetotaxy, stylophore and striae of the dorsal integument, and variations of leg setal counts and length of idiosomal setae in Aponychus corpuzae are discussed. The following changes were observed during the ontogenetic development of A. corpuzae: the depth of the depression in stylophore increases; the dorsal striae gradually reduce in number and prominence; the length of dorsal setae sc1, c12, d12 and e1 reduce in size; adult dorsal setae much thicker than those of immature stages. There are a significant number of setae suppressed in A. corpuzae, often resulting in unique patterns and sexual dimorphism. The adult males and females of Aponychus firmianae and A. taishanicus from mainland China are redecribed, and a key to all Aponychus from mainland China is provided.

Redescription of Panonychus caglei Mellott, 1968, with ontogenetic development (Acari: Tetranychidae).

A redescription of the adult stages of Panonychus caglei Mellott, 1968 (Acari: Tetranychidae), is presented based on new material collected from Japan, and type specimens (holotype and paratypes). Morphological differences in the setation of legs have been reported and measurements of taxonomic characters are added. We also have described the ontogenetic development of the juvenile stages. The ventral idiosomal chaetotaxy in larval stage lacks pregenital and genital setae which are added consecutively through development. The pregenital pair of setae appears in the protonymphs while the first pair of genital setae is firstly observed in the deutonymphal stage.

A simple PCR-based method for the rapid and accurate identification of spider mites (Tetranychidae) on cassava.

The morphological identification of mites entails great challenges. Characteristics such as dorsal setae and aedeagus are widely used, but they show variations between populations, and the technique is time consuming and demands specialized taxonomic expertise that is difficult to access. A successful alternative has been to exploit a region of the mitochondrial cytochrome oxidase I (COI) gene to classify specimens to the species level. We analyzed the COI sequences of four mite species associated with cassava and classified them definitively by detailed morphological examinations. We then developed an identification kit based on the restriction fragment length polymorphism-polymerase chain reaction of subunit I of the COI gene focused on the three restriction enzymes AseI, MboII, and ApoI. This set of enzymes permitted the simple, accurate identification of Mononychellus caribbeanae, M. tanajoa, M. mcgregori, and Tetranychus urticae, rapidly and with few resources. This kit could be a vital tool for the surveillance and monitoring of mite pests in cassava crop protection programs in Africa, Asia, and Latin America.

Molecular and phenotypic variations in Eutetranychus orientalis (Klein) populations from Saudi Arabia.

The oriental red spider mite, Eutetranychus orientalis (Klein) is a major pest of citrus in many countries including Saudi Arabia (SA). The morphological variations among the different populations of E. orientalis were reported. In the present study, phenotypic variations based on 40 different morphological characteristics were evaluated in 10 E. orientalis populations collected from different hosts and regions of SA. Further, ITS2-rDNA sequences were used to confirm the identity of these phenotypically varying populations. Phenotypic variations in all populations were found in the shape and length of dorsal setae, striation pattern between setae d1 and e1, and leg chaetotaxy. The rDNA sequence analysis of these morphologically varying populations resulted in 10 different ITS2 Saudi haplotypes. The phenotypic and genetic variations were more related to the host plants rather than their geographic distribution. The E. orientalis population collected from Phoenix dactylifera was phenotypically distinct and genetically divergent. The populations collected from citrus species were also more phenotypically and genetically related to each other than to populations collected from non-citrus host plants. The haplotypes recovered from Ziziphus sp., Morus sp., and Azadirecta indica from different regions were grouped in the same sub-clade. Further, the ITS2 haplotypes of Saudi E. orientalis recovered from Citrus reticulata from Riyadh and Al Ula were 100% identical to the ITS2 haplotypes recovered from Citrus sp. from Israel. It is concluded that phenotypic variations exist among different populations of E. orientalis inhabiting different host plants. This species should be identified carefully by considering phenotypic intraspecific variations.

Morphological identification of Amphitetranychus species (Acari: Tetranychidae) with crossbreeding, esterase zymograms and DNA barcode data.

The genus Amphitetranychus Oudemans (Tetranychidae) consists of only three species, A. quercivorus (Ehara & Gotoh), A. savenkoae (Reck) and A. viennensis (Zacher). The original description of A. savenkoae was extremely simple and had no drawing of the aedeagus; however, a subsequent study described only the aedeagus. The present study investigated all three species in detail using a combination of morphological traits, crossbreeding experiments, esterase zymograms and the mitochondrial cytochrome c oxidase subunit I (COI) gene. Morphological differences in the peritremes and male aedeagi were observed among the three species. Complete reproductive isolation was confirmed in the reciprocal crosses between the morphologically similar A. savenkoae and A. quercivorus (no female offspring were produced). Esterase zymograms differed interspecifically, but not intraspecifically (among individuals in a given species). All three species formed clearly separate clades with 100% bootstrap values in the COI tree, and A. savenkoae was more closely related to A. quercivorus than to A. viennensis, which corresponded to the morphological similarity of their aedeagi and setal counts on tarsi IV. A key to Amphitetranychus species is provided.

Graphene oxide as a pesticide delivery vector for enhancing acaricidal activity against spider mites.

Synergistic combination of pesticides and nanomaterials has been rarely reported in pest management science at present. In this work, graphene oxide (GO) was synergistically used with three types of pesticides (pyridaben (Pyr), chlorpyrifos (Chl) and beta-cyfluthrin (Cyf) respectively as acaricide against two economically important spider mites Tetranychus truncatus and T. urticae Koch. The results demonstrated that GO can enhance the activity of three types of pesticides. Compared with pesticides, the GO-Cyf, GO-Pyr and GO-Chl mixtures exhibited 1.77-, 1.56- and 1.55-fold higher contact toxicity against T. truncatus, and 1.50-, 1.75-, and 1.78-fold higher contact toxicity against T. urticae. SEM results showed that pesticide can adsorbed on the surface of GO. The synergistic mechanism may be that GO can serve as a carrier of pesticides, which can be adsorbed on the surface of mites and thus improve efficacy and utilization efficiency of pesticides. This kind of GO-based nanoscale pesticide delivery system may find widespread application in the field of plant protection in the future.

New species, new records and re-description of spider mites (Acari: Tetranychidae) from India.

Two species of Tetranychidae (Acari), Oligonychus neotylus sp. nov. from Zea mays and Pennisetum purpureum (Poaceae) and Tetranychus hirsutus sp. nov. from Gymnema sylvestre R. Br. (Apocynaceae) are described from Karnataka state, south India. Tetranychus bambusae Wang and Ma is recorded for the first time from India and re-described. Four other species are reported for the first time from India viz., Oligonychus coniferarum (McGregor), Oligonychus duncombei Meyer, Tetranychus marianae McGregor and Tetranychus okinawanus Ehara from Cupressus sp., an undetermined grass, Centrosema pubescens and Adenium obesum, respectively.

Panonychus from Georgia: survey, taxonomical status and redescription of P. hadzhibejliae (Reck, 1947) (Acari, Tetranychidae).

A survey of Panonychus species was undertaken across Georgia from 2005 to 2014 on various host plants, revealing three species: Panonychus citri (McGregor, 1916), Panonychus hadzhibejliae (Reck, 1947) and Panonychus ulmi (Koch, 1836). New hosts for P. ulmi and P. citri are recorded, Buxus sempervirens, Hedera colchica and Prunus laurocerasus for P. ulmi and Ficus carica for P. citri, whereas P. hadzhibejliae was only found on F. carica. The newly collected material also allowed us to investigate the taxonomical status of P. hadzhibejliae. The comparison of P. hadzhibejliae with the two closely related species sampled in the survey, P. ulmi and P. citri, and with data of P. caricae found in the literature, shows that P. hadzhibejliae is a valid species. It can be separated from the three other Panonychus species without ambiguity especially using the female dorsal setae length in combination with the ratio between the length of the female dorsal opisthosomal f2 and h1 setae and the ratio between the palptarsal terminal eupathidium su and the related solenidion ω. A redescription of P. hadzhibejliae is provided including the male and some morphological characters, measurements and drawings of the female that were omitted in the original description. A key to the world species of Panonychus is also proposed.

Lethal male combats in Schizotetranychus brevisetosus (Acari: Tetranychidae) on blue Japanese oak (Quercus glauca).

Male spider mites (Acari: Tetranychidae) guard preimaginal quiescent females to reserve paternity. In a few species of Stigmaeopsis that make densely woven silky nests on the surface of host plants, mature males attack and even kill rivals to gain their rights to inseminate young females in the nest. Here we report that the adult males of Schizotetranychus brevisetosus (Acari: Tetranychidae), whose web nest construction behavior evolved independently from Stigmaeopsis spp., also exhibit highly aggressive behavior towards one another. Combat mortality was measured in an experimental design where two males in the treatment group were forced to live in a nest made by adult females on a leaf arena, while one male in the control group was allowed to live in a nest on another arena. We found that the 5-day mortality of males in the treatment group (56 and 37 % in two replicates) was significantly higher than in the control group (9 and 12 %) and that lethal combats frequently arose in the treatment group. However, we found no consistent trend for the length of the first legs, which is known to affect the outcome of battle in Tetranychus urticae and Stigmaeopsis miscanthi. This might be due to a relatively small number of measurable specimens, and the effects of body size should be explored in future studies.

Plant mites of the Dominican Republic, with a description of a new species of Petrobia (Tetranychina) Wainstein, 1960 (Acari, Prostigmata, Tetranychidae) and a key to the species of this subgenus.

Fourteen mite species of plant-associated mites of the suborder Prostigmata are reported from the Dominican Republic. Four of these refer to new findings for the country, including Petrobia (Tetranychina) hispaniola n. sp. Sánchez & Flechtmann, described from specimens collected from leaves of Citrus sp. (Rutaceae) and Rosa sp. (Rosaceae). A key for the separation of the world species of Petrobia (Tetranychina) is presented. 

New species and new records of Tetranychidae (Acarina, Prostigmata) from Thailand.

Sampling efforts conducted in several provinces from Thailand disclosed three new species of tetranychid mites. Two of them belong to the genus Tetranychus, namely Tetranychus occultaspina sp. nov. and Tetranychus truncatissimus sp. nov. and the third species belongs to the genus Schizotetranychus, Schizotetranychus krungthepensis sp. nov. They were collected on Ipomoea aquatica, Bambusa multiplex and Saccharum officinarum, respectively. New records and new hosts are also mentioned. 

Genetic basis of woven nest size in subsocial spider mites.

The variation in nest size of social spider mites of the genus Stigmaeopsis is assumed to correspond to their anti-predator strategy and to be a key aspect of their social organization and speciation. It is known that the length of the dorsal setae (sc1, 2nd propodosomal setae) correlates with the nest size. We conducted interspecies cross experiments to determine the heredity of sc1 length and nest size using two closely related species that build different sized nests, Stigmaeopsis saharai Saito et Mori and Stigmaeopsis takahashii Saito et Mori. A cross between a S. saharai female and a S. takahashii male produced several viable F1 females. We measured sc1 length and the nest size of the F1 females and then compared these values with those of their parent species. The sc1 length of F1 females and the nest size constructed by these mites were intermediate with respect to the values of the two parent species. Therefore, the length of the sc1 and nest size are heritable. This result sheds light on the importance of considering the genetic basis for the variations in social organization.

Alternative phenotypes of male mating behaviour in the two-spotted spider mite.

Severe intraspecific competition for mates selects for aggressive individuals but may also lead to the evolution of alternative phenotypes that do not act aggressively, yet manage to acquire matings. The two-spotted spider mite, Tetranychus urticae, shows male mate-guarding behaviour and male-male combat for available females. This may provide opportunity for weaker males to avoid fighting by adopting alternative mating behaviour such as sneaker or satellite tactics as observed in other animals. We investigated male precopulatory behaviour in the two-spotted spider mite by means of video-techniques and found three types of male mating behaviour: territorial, sneaker and opportunistic. Territorial and sneaker males associate with female teleiochrysales and spend much time guarding them. Territorial males are easily disturbed by rival males and engage themselves in fights with them. However, sneaker males are not at all disturbed by rival males, never engage in fights and, strikingly, never face attack by territorial males. Opportunistic males wander around in search of females that are in the teleiochrysalis stage but very close to or at emergence. To quickly classify any given mate-guarding male as territorial or sneaker we developed a method based on the instantaneous response of males to disturbance by a live male mounted on top of a brush. We tested this method against the response of the same males to natural disturbance by two or three other males. Because this method proved to be successful, we used it to collect territorial and sneaker males, and subjected them to morphological analysis to assess whether the various behavioural phenotypes are associated with different morphological characters. However, we found no statistical differences between territorial and sneaker males, concerning the length of the first legs, the stylets, the pedipalps or the body.

Relationship between body colour, feeding, and reproductive arrest under short-day development in Tetranychus pueraricola (Acari: Tetranychidae).

In Tetranychus spider mites (Acari: Tetranychidae), diapausing females have a conspicuous orange body colour, which is used as an indicator of diapause induction in many laboratory studies. However, to which extent body colour reflects reproductive activity is scarcely investigated. In this study, we investigated the relationship between body colour, reproductive arrest, and food intake in the inbred strain of T. pueraricola individually reared at 20 °C with a 10:14 h light: dark photoperiod. Our results showed that (1) body colour is a good indicator of reproductive arrest 11 days after adult emergence but does not completely reflect reproductive status at an earlier age; (2) even orange females intermittently feed, and the arrest of feeding comes after the change in body colour; and (3) reproducing females have a higher risk of death than non-reproducing females. These results suggest that measurement of diapause incidence by body colour alone may miss the variation in reproductive status in early adult life.

Asymmetry in male lethal fight between parapatric forms of a social spider mite.

Closely related species often show adjacent geographic distributions, albeit with some overlap. This contiguity is thought to result from secondary contact between (spatially separated) diverging groups or from parapatric speciation. Fights between males of closely related species will affect their chance to mate with females of the other species, which in turn may promote their spatial segregation and drive their speciation. Stigmaeopsis miscanthi is a social spider mite that lives in a group within self-woven nests on leaves of Chinese silver grass. This mite shows lethal male-male fight as a means to maintain a harem, and has two forms showing differences in the levels of male-male aggression, diapause intensity in females and the relative length of the first to third legs. The two forms show parapatric distributions. We found that males of one form readily engage themselves in lethal fight with males of the other form, thereby acquiring the nests and gaining access to females of this other form. Males of the aggressive form tend to win the fights with males of the other form. Their first legs are longer which may provide them with a better weapon and which also indicate a larger body width. However, another determinant of who wins the fight is the length of the third legs which can be a proxy for body length. Based on these results, we hypothesize that male killing behavior is one of the mechanisms maintaining parapatry (instead of sympatry) of the two spider mite forms apart from difference in diapause attributes.

Should I lay or should I wait? Egg-laying in the two-spotted spider mite Tetranychus urticae Koch.

Optimality theory predicts that females tend to maximize their offspring survival by choosing the egg-laying site. In this context, the use of conspecific cues allows a more reliable assessment of the habitat quality. To test this hypothesis, Tetranychus urticae Koch is an appropriate biological model as it is a phytophagous mite living in group, protected against external aggression by a common web. Experiments were conducted to determine the respective influence of substrate (living substrate: bean leaf vs. non-living substrate: glass plate), silk and presence of conspecific eggs on the egg-laying behavior of T. urticae females. On both living and non-living substrates, the presence of silk positively influenced the probability of a female to lay an egg, but had no influence on the number of eggs deposited. The egg-laying behavior was mainly determined by the nature of the substrate with mites laying fewer eggs on a non-living substrate than on a living one. The presence of a conspecific egg had no impact on either the probability of laying an egg or on the oviposition rate. This study showed a high variability among females in their fecundity and egg-laying performance. The physiology of females (individual fecundity), the egg-laying substrate and to a lesser extent the presence of silk impacted on the decision of spider mites to lay eggs.

Life history differences between two forms of the social spider mite, Stigmaeopsis miscanthi.

The two forms of Stigmaeopsis miscanthi (Saito) (called LW and HG) differ in their levels of male-to-male aggression, differ in their diapause attributes, and morphologically in the male leg I armor. Furthermore, a type of reproductive isolation exists between the forms, although some one-way compatibility is maintained. Here we looked for any differences in life history traits between the two forms under experimental conditions. The intrinsic rate of natural increase (r(m)) of the LW form was lower than that of the HG form, the difference seemingly caused by the developmental speed of the latter. Although the developmental speeds of HG under several temperature regimens were significantly higher than those of LW, the low development threshold temperatures of the two forms were almost identical. This study addresses why a significant difference in r(m) exists in relation to other behavior and physiological (diapause) adaptations.

Ontogenetic development and redescription of Tribolonychus collyerae (Acari: Tetranychidae).

Tribolonychus collyerae Zhang & Martin is redescribed based on the larva, protonymph, deutonymph and adult male and female specimens from New Zealand. The ontogenetic development of chaetotaxy in Tribolonychus and the number and position of solenidia on tibia I are discussed. Patterns of setal addition on leg III and IV from larva to adult in Trilobonychus are different from the basic pattern of the Tetranychinae and allied genus Neonidulus.

A new species of the genus Sonotetranychus (Acari: Tetranychidae) from New Zealand.

The genus Sonotetranychus consisted of seven species prior to this study. Sonotetranychus menziesii sp. nov., collected on Nothofagus menziesii and N. fusca from New Zealand, is described based on females, protonymphs, deutonymphs and a male. An updated key to the species of Sonotetranychus is provided.

The influence of sublethal deposits of agricultural mineral oil on the functional and numerical responses of Phytoseiulus persimilis (Acari: Phytoseiidae) to its prey, Tetranychus urticae (Acari: Tetranychidae).

Occasional pesticide application in integrated pest management to at least part of a crop requires that any biological control agents must re-invade previously sprayed areas in order that resurgent pests can be constrained. The ability of the phytoseiid predatory mite Phytoseiulus persimilis to feed on adult two-spotted spider mite (TSSM) Tetranychus urticae on excised leaf discs in both control conditions and in a treatment with a sub lethal residue of agricultural mineral oil (AMO) was assessed. The predator exhibited a Type II functional response with the asymptote significantly higher in the AMO conditions due to the fact that the prey grew slower and reached a smaller size in this treatment. In terms of prey volume eaten, the satiation level of the predator was unchanged by the AMO deposits. The numbers of eggs produced by adult P. persimilis females at densities of 4, 8 and 16 TSSM adult females/disc in the control were significantly higher than those in the AMO treatment, but were similar for the higher density levels, 32 and 64 prey per disc. Thus the functional response in terms of volume of prey eaten explained the numerical response in terms of predator eggs produced. The presence of AMO deposits when the prey were at high density had no effect on predator efficiency (volume eaten) but resulted in a lower intake than that in control conditions when there was a greater distance between prey.