Characteristics of development and reproduction in Typhlodromus pyri on Tetranychus urticae and Cecidophyopsis ribis. II. Progeny of overwintered females

The results of this study on the bionomic parameters in progeny of overwintered females of Typhlodromus pyri Scheuten under constant laboratory conditions (18°C, R.H. 75%. 18L:6D) are described. The predatory mites were fed overwintering forms of two prey species, the two-spotted spider mite. Tetranychus urticae Koch and the black currant gall mite. Cecidophyopsis ribis (Westwood). The results corroborate that T. pyri is able to complete its life-cycle and reproduce when it feeds exclusively on the black currant gall mite. Juvenile development of females feeding on T. urticae and on C. ribis was 19.4 and 20.9 days respectively, while in males it was 18.4 and 17.5 days. Mortality of juveniles feeding on T. urticae was higher (33.0%) compared with that of juveniles fed on C. ribis (10.7%). The highest mortality was noted in protonymphs fed on T. urticae (21.9%). The difference between the mean total fecundity of females fed on T. urticae (16.4 eggs) and on C. ribis (17.8 eggs) was not statistically significant. Mean duration of preoviposition, oviposition and postoviposition periods were 19.1, 25.0 and 14.5 days in females fed on T. urticae and 19.7. 50.2 and 5.0 in those fed on C. ribis.     

Simulating effects of environmental factors on biological control of Tetranychus urticae by Typhlodromus pyri in apple orchards

Successful biological control of mites is possible under various conditions, and identifying what are the requirements for robust control poses a challenge because interacting factors are involved. Process-based modeling can help to explore these interactions and identify under which conditions biological control is likely, and when not. Here, we present a process-based model for population interactions between the phytophagous mite, Tetranychus urticae, and its predator, Typhlodromus pyri, on apple trees. Temperature and leaf nitrogen concentration influence T. urticae rates of development and reproduction, while temperature and rate of ingestion of prey and pollen influence T. pyri rates of survival and reproduction. Predator and prey population dynamics are linked through a stage structured functional response model that accounts for spatial heterogeneity in population density throughout the trees. T. urticae biomass-days (BMD’s), which account for sizes of larvae, nymphs and adults, indicate level of mite-induced leaf damage. When BMD’s exceed 290 per leaf, there are economic losses. When BMD’s exceed 350 per leaf, T. urticae population growth is curbed and eventually the population decreases. Simulations were run to determine which conditions would lead to current year economic loss and increased risk of loss in the following year, i.e. where more T. urticae than T. pyri are present at the end of September. Risk was high with one or more of the following initial conditions: a high prey: predator ratio (10:1 or more); a low to intermediate (0.04–0.2 T. urticae per leaf) initial density; T. urticae with a higher initial proportion of adult females than T. pyri; and a delayed first detection of mites, whether in late July, or sometimes in late June, but not in early June. Warm summer weather, higher leaf nitrogen and T. urticae immigration into trees were also risk factors. Causes for these patterns based on biological characteristics of T. urticae and T. pyri are discussed, as are counter measures which can be taken to reduce risk.     

Biological control of the two-spotted spider mite Tetranychus urticae on strawberries by the predatory phytoseiid mite Typhlodromus pyri (Acari, Tetranychidae, Phytoseiidae)

The ‘Mikulov’ strain of the predatory mite Typhlodromus pyri Scheuten from south Moravian vineyards was released on cultivated strawberries infested with the two-spotted spider mite, Tetranychus urticae Koch. The strawberries were grown in field plantations and under glass. Typhlodromus pyri on vine shoots were successfully introduced into the field strawberry plantation but they produced no demonstrable control of the spider mites and they eventually declined in density with their prey. In contrast, T. pyri gave good control of spider mites in the glasshouse despite the occurrence of low humidity and water stress of the plants.     

Larval survival and feeding by immature Metaseiulus occidentalis,Neoseiulus fallacis,Amblyseius andersoni and Typhlodromus pyri on life stage groups of Tetranychus urticae Koch and phytoseiid larvae

When 20 newly hatched larvae either of Metaseiulus occidentalis (Nesbitt), Neoseiulus fallacis (Garman), Amblyseius andersoni Chant or Typhlodromus pyri Scheuten were held in arenas without food at 95% RH and 20°C, the percentages of mites surviving to protonymphs were 5.0, 81.3, 86.3, and 83.8%, respectively. Unfed M. occidentalis larvae starved within 2–3 days, while immatures of the other three species lived up to 12–14 days, with some becoming adults by cannibalizing and/or scavenging. Phytosciid larvae given eggs, larvae/protochrysalis/protonymphs (L/P), deutochrysalis/deutonymphs (D) or teleiochrysalis/female adult (T/A) of Tetranychus urticae Koch, fed at different incidences during 6 h tests. Larvae of T. pyri never fed, but almost all larvae of M. occidentalis fed on eggs and L/Ps and 60–70% of M. occidentalis larvae fed on Ds and T/As. N. fallacis and A. andersoni larvae fed at incidences from 20–75% depending on the stage of spider mite given. Larvae fed more commonly on eggs and L/Ps than Ds and T/As for M. occidentalis and N. fallacis but not A. andersoni. Protonymphs and deutonymphs of all four species, readily fed on T/As after 3 h of exposure, but incidences were higher for A. andersoni and T. pyri. Feeding on phytoseiid larvae by protonymphs and deutonymphs also was more common for A. andersoni and T. pyri. Except for M. occidentalis, deutonymphs fed more than protonymphs on phytoseiid larvae. Results are discussed in relation to individual species life histories and the value of these traits in predicting a species role in a biological control system.     

Sublethal effects of esfenvalerate residues on pyrethroid resistant Typhlodromus pyri (Acari: Phytoseiidae) and its prey Panonychus ulmi and Tetranychus urticae (Acari: Tetranychidae)

The effect of residues of esfenvalerate on oviposition of the resistant strain of the predatory mite Typhlodromus pyri and its main prey, European red mite Panonychus ulmi and two-spotted spider mite Tetranychus urticae, were investigated. T. pyri showed a significant linear reduction in oviposition after 24h in the presence of increasing levels of esfenvalerate residue applied at the field rate. Furthermore, when given a choice, T. pyri preferred to lay eggs on residue-free surfaces. Of the two prey species, only P. ulmi showed significant avoidance of increasing levels of residues of the field rate concentration of esfenvalerate, as measured by runoff mortality, however both P. ulmi and T. urticae, when given a choice, showed a preference for esfenvalerate-free surfaces. As with the predatory mite T. pyri, both prey species showed a significant linear reduction of oviposition with increasing esfenvalerate residues and a preference to lay eggs on esfenvalerate-free surfaces. Esfenvalerate residues as high as 15X field rate were not repellent to pyrethroid-resistant T. pyri. The possible effects of these sublethal effects on predator-prey dynamics and implications for integrated mite control programmes in apple orchards are discussed.     

Walking,feeding and intraspecific interaction of larvae of Metaseiulus occidentalis,Typhlodromus pyri,Neoseiulus fallacis and Amblyseius andersoni held with and without eggs of Tetranychus urticae

Larvae of Metaseiulus occidentalis (Nesbitt), Typhlodromus pyri Scheuten, Neoseiulus fallacis (Garman) and Amblyseius andersoni Chant exhibited different activity levels when held on apple leaf or on tile arenas and given or not given eggs of Tetranychus urticae Koch and water (tiles only). M. occidentalis larvae held without prey exhibited high levels of walking (includes searching) during 24 hours of evaluation, whereas M. occidentalis larvae held with prey fed quickly and then became less active. Fed larvae of M. occidentalis were less active on leaves than tile. Larvae of T. pyri on leaves had a very low frequency of walking, almost never fed and quickly assumed a resting position during development. While much less active than M. occidentalis, fed and unfed T. pyri larvae walked more on tiles than leaves before resting. Larvae of N. fallacis and A. andersoni fed at low rates and were similarly active on tiles and leaves. Free water increased walking by M. occidentalis, A. andersoni and T. pyri on tile but not N. fallacis. M. occidentalis larvae interacted 5–7 times more often than larvae of the other three species. Cannibalism or scavenging was rarely seen and then only for M. occidentalis larvae. Larvae of all four mites walked, fed and interacted much more in the first 12 hours than the second 12 hours of tests, except unfed M. occidentalis. Unfed M. occidentalis larvae did not molt to protonymphs but unfed larvae of the other three species did. Unfed and fed protonymphs of all four species walked more at 4 hours after molting than larvae at 12–24 hours. Unfed and fed protonymphs of T. pyri or A. andersoni had similar walking frequencies, but unfed protonymphs of N. fallacis were more active than fed ones. Trends in larval activities are discussed relative to the life history of each species.     

二斑叶螨的卵和丝网对西花蓟马生长发育和繁殖的影响

为探讨二斑叶螨Tetranychus urticae Koch的卵和丝网对西花蓟马Frankliniella occidentalis(Pergande)的影响,本文研究了西花蓟马分别取食健康菜豆叶片、带二斑叶螨卵的菜豆叶片、带卵+丝网的菜豆叶片3种不同情况下,西花蓟马生长发育、存活和繁殖情况,并获得了其生命参数。结果表明西花蓟马在带二斑叶螨卵的菜豆叶片上发育最快,其未成熟期为11.35 d,明显短于另外两个处理,在带有二斑叶螨卵和丝网的菜豆叶片上成虫获得率最低为63%,西花蓟马在不同处理之间的成虫寿命和繁殖力没有明显的差异;西花蓟马取食3种菜豆叶片的内禀增长率分别为0.1779、0.1827和0.1710。以上结果说明取食二斑叶螨的卵可缩短西花蓟马发育时间,对种群增长有利,二斑叶螨的丝网可降低西花蓟马的存活率。     

二斑叶螨对六种植物的选择性及生长发育

采用“Y”形嗅觉仪研究二斑叶螨Tetranychus urticae Koch对接骨木(Sambucus williamsii Hance)、苹果(Malus pumila Mill.)、木瓜(Chaenomeles sinensis Koehne)、苦楝(Melia azedarach L.)、火炬树(Rhus typhina Torner)、大叶黄杨(Euonymus japonica Thunb)6种植物的嗅觉选择性差异。结果表明,该螨对苹果叶片的气味表现明显的趋向性,对木瓜叶片的气味表现明显的忌避性,而对其余4种叶片无趋向性或者表现中性。采用海绵水盘法研究在6种植物上的生长发育差异,该螨在接骨木、苹果、苦楝、火炬树上均能正常生长发育至成螨,且具有一定的繁殖力。但在木瓜和大叶黄杨上发育状况较差,繁殖力较差。     

Effects of constant and variable temperatures on development and reproduction of the two-spotted spider mite Tetranychus urticae (Acari: Tetranychidae)

We focused on the influence of different temperature amplitudes on development and reproduction of the two-spotted spider mite, Tetranychus urticae Koch, at a 16:8 (L:D) h photoperiod and 60–95 % RH. The temperature amplitudes varied from 0 to 24 °C in steps of 6 °C; i.e. 22 ± 0, 22 ± 3, 22 ± 6, 22 ± 9 and 22 ± 12 °C. Temperature changed every 24 h between a low and an upper value, but without changing the average temperature (22 °C). The number of eggs laid by five females for 24 h was slightly lower at 22 ± 12 °C than at constant temperature (22 ± 0 °C), and egg hatchability differed among the five temperature regimes. Developmental time at 22 ± 0 °C was shorter than that at 22 ± 3 and 22 ± 6 °C, but longer than that at 22 ± 9 and 22 ± 12 °C. The oviposition period, total fecundity per female and adult longevity gradually decreased with increasing amplitudes. Sex ratio was similar at all five temperature regimes. The intrinsic rate of natural increase (r _m) was affected by temperature amplitude and the r _m-values at all amplitudes except 22 ± 12 °C were higher than that at constant temperature. Thus, this study showed that variable temperature regimes influence population growth rates of T. urticae and that large amplitude regimes are stressful for this species.     

Temperature-related development and population parameters for Typhlodromus pyri (Acari: Phytoseiidae) found in Oregon vineyards

The beneficial mite Typhlodromus pyri is a key predator of grapevine rust mite Calepitrimerus vitis in Pacific coastal vineyards. Rust mite feeding has been associated with damage such as stunted, deformed shoot growth and reductions in fruit yield. The life history traits of T. pyri were assessed at seven constant temperatures (12.5, 15, 17.5, 20, 25, 30 and 35 °C) to determine population parameters providing data to better predict biological control of C. vitis populations by T. pyri in vineyards. Successful development from the egg to adult stage was observed at temperatures ranging from 15 to 30 °C. Constant exposure to 12.5 and 35 °C resulted in 100 % mortality in immature T. pyri. Developmental times, fecundity and longevity were highest at 25 °C. The estimated minimum and maximum developmental thresholds were 7.24 and 42.56 °C, respectively. Intrinsic rate of increase (r ( m )) was positive from 15 to 30 °C indicating population growth within this range of temperatures. Net reproductive rate and intrinsic rate of increase were greatest at 25 °C. These developmental parameters can be used to estimate population growth, determine seasonal phenology and aid in conservation management of T. pyri. Results presented in this study will aid in evaluating the effectiveness of T. pyri as a key biological control agent of C. vitis during different periods of the growing season in Pacific Northwest vineyards.     

Biparental inheritance of RAPD markers in males of the pseudo-arrhenotokous mite Typhlodromus pyri.

In pseudo-arrhenotokous mites, haploid males develop from fertilized eggs that undergo paternal genome loss (PGL) during early embryogenesis. We present evidence that some of the paternal genome may be retained in males of the predatory mite Typhlodromus pyri Scheuten (Acari: Phytoseiidae). Two reproductively compatible populations were differentiated by two random amplified polymorphic DNA markers and the inheritance pattern in the offspring was analysed. Maternal transmission rates are variable and independent of the sex of the offspring and of the marker. These data suggest a nuclear origin and independent segregation of the markers. One marker (330 base pairs (bp)) was paternally transmitted to male as well as female offspring, the other (990 bp) was paternally transmitted to all females and some of the male offspring. We propose that the paternal set of inactivated chromosomes may be partially retained in some tissues of the haploid males or, alternatively, that a B chromosome does not follow the process of PGL in male embryos, thereby segregating with the maternal set. The possible mechanisms controlling the condensation and the segregation of the chromosome(s) retained are discussed on the basis of current hypotheses on chromosome inactivation in insects.     

Intra- and interspecific predation by adult female Metaseiulus occidentalis and Typhlodromus pyri (Acari: Phytoseiidae) when provisioned with varying densities and ratios of Tetranychus urticae (Acari: Tetranychidae) and phytoseiid larvae

The phytoseiid mites Metaseiulus occidentalis (Nesbitt) and Typhlodromus pyri Schueten are used together and alone as biological control agents against tetranychid pest mites of apple. Their effectiveness as control agents may be impacted by intraguild predation. The effects of prey species and prey density on the rates of inter- and intraspecific predation and oviposition by these two predators were investigated through a series of experiments. Adult female predators were given prey as mixed populations of phytoseiid larvae and larvae of a more preferred species, the spider mite, Tetranychus urticae Koch, at different densities and ratios. Typhlodromus pyri, more of a generalist predator, showed higher rates of predation and cannibalism on phytoseiid immatures at most prey densities and ratios. Manly preference indices indicated that T. pyri switched to feed on phytoseiid larvae at higher prey levels and ratios of T. urticae than M. occidentalis. This greater ability to use phytoseiid larvae as prey may help stabilize T. pyri populations when more preferred prey is unavailable. This may, in part, explain the observed persistence of T. pyri populations when M. occidentalis populations were decreasing in orchard test plots.     

Rapid development of 36 polymorphic microsatellite markers for Tetranychus truncatus by transferring from Tetranychus urticae

Tetranychus truncatus Ehara is a phytophagous spider mite that is now one of the most important pests of agricultural and economic crops in East and Southeast Asia. However, population genetics and other studies of T. truncatus have been impeded by the lack of microsatellite markers, which are expensive and time-consuming to identify. Previous studies indicated a high potential of cross-amplification of microsatellites in Tetranychus species, meaning that the microsatellite flanking sequences are sufficiently homologous among Tetranychus species that the primers for one species may work in another species. Here, we tested 205 primer pairs designed from the whole genome sequence of Tetranychus urticae Koch, a sister species of T. truncatus, for microsatellite markers in three populations of T. truncatus in China (N = 94). About half (102) of these primer pairs yielded the desired PCR products, 36 of which revealed polymorphism in T. truncatus. Each of the 36 markers harbored between 2 and 23 alleles, with a mean polymorphic information content of 0.589 (0.119–0.922 range). The mean observed and expected heterozygosity across loci and the three populations were 0.468 and 0.628, respectively. Of the 36 primer pairs, 22 also worked in Tetranychus piercei, but only a few of them worked in T. ludeni and T. phaselus. Cross-amplification is thus a cost-effective way to develop microsatellite markers, which can be of great value in population genetics studies.     

Inter- and intraspecific predation on immatures by adult females in Euseius finlandicus, Typhlodromus pyri and Kampimo dromus aberrans (Acari: Phytoseiidae)

In a series of experiments, the interspecific predation and cannibalism on immatures by the adult females of Euseius finlandicus, Kampimodromus aberrans and Typhlodromus pyri were examined under laboratory conditions. The three species showed differing tendencies to prey on each other's motile immature stages. Euseius finlandicus females consumed more larvae and protonymphs than the females of T. pyri and K. aberrans. In cages without free water E. finlandicus ate a range of 6.51 larvae or 5.31 protonymphs of T. pyri and 5.27 larvae or 5.95 protonymphs of K. aberrans per female per day. Kampimodromus aberrans and T. pyri females exhibited a greater tendency to prey on heterospecifics than on conspecifics. When feeding on phytoseiid immatures and without free water, T. pyri females survived longer and laid more eggs than the females of E. finlandicus and K. aberrans. Adult females of E. finlandicus and T. pyri having free water and preying on heterospecific protonymphs were able to maintain egg laying during the whole experimental period of 12 days. The females of all three species had difficulties in piercing phytoseiid eggs, and the number of sucked eggs per female per day was low. Kampimodromus aberrans females ate 0.48 eggs of T. pyri daily, which was the highest recorded number. The great tendency to interspecific predation on motile immature phytoseiids by the females of E. finlandicus is discussed with regard to the dominance of this species on deciduous trees and bushes in Austria.     

二斑叶螨发生危害特点及防治对策

本文介绍了二斑叶螨在我国的危害情况和发生规律 ,分析了其发生与危害的特点 ,并提出了有效防治对策     

Response to photoperiod during diapause development in the spider mite Tetranychus urticae

To study the question whether photoperiodic time measurement in the spider mite Tetranychus urticae is based on a qualitative or quantitative principle, the duration of diapause development was determined in individual females at various constant photoperiods at 19 degrees C. Diapause duration at all four long-night treatments fluctuated around 64.5 days, varying from 62.2 at LD 12:12h to 66.4 at LD 10:14h. The within-treatment variation in diapause duration of the long-night groups appeared to be significantly correlated to the nightlength of the photoperiods used; the longer the nightlength, the higher the within-treatment variation. Frequency distributions of females completing diapause under the two regimes with nightlengths near the critical nightlength were skewed to the right. Mean diapause durations at these regimes, LD 13:11h and LD 14:10h, were 25.4 and 11.9 days, respectively. Mites completed diapause rapidly and synchronously under the three short-night photoperiods tested; within two weeks after transfer from cold storage at 4 degrees C to the diapause terminating regimes at 19 degrees C all females started reproduction. Mean diapause durations were 8.1, 6.4 and 6.5 days for the short-night treatments LD 15:9h, LD 17:7h and LD 19:5h, respectively. The coefficients of variation of diapause duration (variability within groups relative to the mean) of the short-night and the long-night groups varied from 18 to 42%; the coefficients of the two intermediate groups were 69and 81%. There was a clear difference in diapause duration between long-night and short-night groups, but no significant difference was present in this characteristic between different long-night groups on the one hand and only a small difference between different short-night groups on the other. These results support the hypothesis that photoperiodic time measurement in the spider mite is based on a qualitative principle; photoperiods are classified as either 'long' or 'short' in relation to a 'critical' photoperiod. However, around the critical nightlength, intermediate responses were observed which might hint at the quantitative nature of the underlying mechanism. Therefore, although most results are in agreement with the hypothesis of a qualitative mechanism, it cannot be excluded that photoperiodic time measurement in the spider mite is based on a quantitative principle.     

Influence of leaf trichomes on predatory mite (Typhlodromus pyri) abundance in grape varieties

Non-glandular leaf trichomes positively influence the abundance of many phytoseiid mites. We characterized the influence of grape leaf trichomes (domatia, hairs, and bristles) on Typhlodromus pyri Scheuten abundance over two years in a common garden planting of many grape varieties and 2 years of sampling in a commercial vineyard. In general, a lack of trichomes was associated with much lower predator numbers and in the case of Dechaunac, a cultivar with almost no trichomes, very few T. pyri were found. Phytoseiid abundance was best predicted by a model where domatia and hair had an additive effect (r (2) = 0.815). Over two years of sampling at a commercial vineyard there were T. pyri present on all of the 5 cultivars except Dechaunac. At the same time, European red mite prey were present on Dechaunac alone. These results suggest that on grape cultivars lacking leaf trichomes, T. pyri likely will not attain sufficient densities to provide biological control of European red mite, despite presence of the mite food source. The relationship between leaf trichomes and phytoseiid abundance that is observed at the scale of single vines in a garden planting appears to also be manifest at the scale of a commercial vineyard. Because persistence of predatory mites in or nearby the habitats of prey mites is important for effective mite biological control, leaf trichomes, through their influence on phytoseiid persistence, may be critical for successful mite biological control in some systems.     

Intraspecific competition in immature Amblyseius fallacis,Amblyseius andersoni,Typhlodromus occidentalis and Typhlodromus pyri (Acari: Phytoseiidae)

Intraspecific competition in immature Amblyseius fallacis, Amblyseius andersoni, Typhlodromus occidentalis and Typhlodromus pyri was examined in the laboratory using small cages at five different predator densities (two, four, eight, 16 and 32) in the absence and presence of prey 100 eggs of two-spotted spider mite, Tetranychus urticae (Koch), at 25 ± 1°C, 80% RH and 16L:8D photoperiod. In the absence of spider mite prey, some individuals of immature phytoseiids showed increased development and surival with increasing predator densities up to certain limits, but none survived to the adult stage, except for a single male each of A. andersoni and A. fallacis who completed development by cannibalizing on conspecifics at a density of 32 predators per cage. In the absence of spider mite prey, the mean immature survival time was independent of the initial predator density, but the variance of survival time increased with predator density. In the presence of prey, the proportion of immatures surviving to adulthood generally decreased with initial predator density and dropped sharply to almost none at the predator density of 32 for A. fallacis, eight for A. andersoni, 16 for T. occidentalis and four for T. pyri. The number of prey consumed per predator during the first day generally decreased with predator density in all four species, as prey available per predator decreased and the competition for food increased with predator density. Our data indicate that scramble competition is operating in these four species. Although cannibalism was occasionally observed, especially after the exhaustion of prey and in the generalist predators such as A. andersoni, the immatures of these phytoseiids were less influenced by the interference of conspecifics than by the increasing difficulty of finding food at high predator densities. The implications of this study for understanding phytoseiid population dynamics and their use in biological control are discussed.     

Intra- and interspecific predation on four life stage groups by the adult females of Metaseiulus occidentalis, Typhlodromus pyri, Neoseiulus fallacis and Amblyseius andersoni

Do adult females of oligophagous species such as Neoseiulus fallacis (Garman) and Metaseiulus occidentalis (Nesbitt) show less intra- and interspecific predation on phytoseiids when other foods are scarce than polyphagous species such as Amblyseius andersoni Chant and Typhlodromus pyri Scheuten? We caged single adult females of each species without food with ten of their own eggs or larvae, with ten eggs or larvae of the other species or with ten nymphs or adult females of M. occidentalis (T. pyri for M. occidentalis). We assessed the ambulatory activity, survival time, egg levels and prey loss in each test. Polyphages (in particular T. pyri) lived longer than oligophages (in particular N. fallacis) without food. The small T. pyri detected its own stages and benefited most by feeding on small active stages of other species. Amblyseius andersoni, the largest mite, fed and gained the most of any species when held with nymphs and female adults. Metaseiulus occidentalis fed on eggs of all four species to enhance survival. The large hyperactive N. fallacis gained the least from these behaviours. Each mite seemed uniquely adapted to survive conditions of scarce prey and these behaviours may explain their roles in phytoseiid mite complexes. Overall, oligophagous adult females fed less and gained less by feeding on phytoseiids than did polyphagous adult females.