Short Communication: Modification of a leaf-washing apparatus for the recovery of mites

Boller's funnel and sieve apparatus for extracting phytoseiid mites (Acari: Phytoseiidae) from leaves was modified. The modification consisted of including a reservoir dish enabling the placing of the whole sample of leaves into the apparatus, attaching a collecting chamber, simplification of the fixing of the fine lower sieve and adding an upper fine sieve. This modification enables the rapid processing of samples of up to 150 leaves.     

Host plant acceptance by the phytophagous mite Tetranychus kanzawai Kishida is affected by the availability of a refuge on the leaf surface

We used 11 wild plants to experimentally test the effects of leaf trichomes and leaf quality on host plant acceptance by a phytophagous spider mite, Tetranychus kanzawai, in the absence of predators. There was a positive correlation between leaf hair traits (height/density) and host plant acceptance. We used two model plants (Phaseolus vulgaris and Phaseolus lunatus; the former had higher and denser leaf hairs than the latter) to examine the effects of leaf hairs on the dispersal and fecundity of T. kanzawai in the presence of a predatory mite, Neoseiulus womersleyi. In the presence of N. womersleyi, significantly fewer T. kanzawai females dispersed from a P. vulgaris leaf than from a P. lunatus leaf. Moreover, in the presence of the predator the fecundity of T. kanzawai females on P. lunatus was significantly lower than on P. vulgaris, although in terms of host quality the two plants were equivalent. In the presence of N. womersleyi, T. kanzawai females on P. vulgaris spent more time on webs than those on P. lunatus. Moreover, webs seemed to be less accessible than leaf surfaces to the predator. These results suggest that leaf hairs provide a refuge for T. kanzawai adult females.     

Selection of biting sites on a human host by shape Anopheles gambiae s.s., shape An. arabiensis and shape An. quadriannulatus

Adult females of the predatory mite Phytoseiulus persimilis Athias-Henriot are strongly attracted to infochemicals released by plants infested with their prey, the two-spotted spider mite (Tetranychus urticae Koch), thereby effectively locating their prey. However, we found a consistently lower degree of attraction to these infochemicals for a population of P. persimilis, which is called non-responding population. Here we demonstrate that this low degree of attraction is a contagious phenomenon and that it cannot be explained by differences in abiotic conditions, physiological state and experience of predators or by genetic differences between predator populations. Female predators exposed to dead conspecifics of the non-responding population and their products showed a lower degree of attraction to plant odours and a higher mortality than predators exposed to products of a living conspecific of the non-responding population. This was true 6–7 days after contact with dead conspecifics and their products whereas 2 days after contact no effects were detected. The present results are discussed in view of our hypothesis that the change in foraging behaviour as well as the high mortality rate are symptoms of a contagious disease affecting the non-responding population.     

Powdery mildew (Ascomycotina: Erysiphales) — an alternative food for the predatory mite Typhlodromus pyri Scheuten (Acari: Phytoseiidae)

The ability of Typhlodromus pyri Scheuten to feed on powdery mildew was investigated. Adult females of T. pyri which had previously been fed on the pollen of Pinus sylvestris L. were offered three powdery mildew species and their feeding behaviour was observed. The females fed readily on the conidia of Erysiphe orontii Cast. from tobacco and Oidium fragariae Harz. from strawberry while no feeding was observed on Erysiphe polygoni DC. from red clover, even after the mites were starved for 2 days. Erysiphe orontii was tested for its effect on the survival, oviposition and development of T. pyri. The results showed that the conidia of E. orontii can supply mites with the water and nutrients necessary for their normal development. Mature females successfully mated and reproduced, although their oviposition rate was low. This revised version was published online in November 2006 with corrections to the Cover Date.     

Prey stage preference and functional response of the predatory mite Galendromus flumenis to Oligonychus pratensis

The Banks grass mite, Oligonychus pratensis (Banks) (Acari: Tetranychidae), is a serious pest in dates (Phoenix dactylifera L.) in the New World. Currently O. pratensis is managed using the miticide, Savey, and alternative strategies are necessary to remove pressure from a single control method due to the risk of resistance evolution. For this purpose, studies are underway to develop biological control strategies using the predatory mite, Galendromus flumenis (Chant) (Acari: Phytoseiidae). The current study determined the consumption rate of G. flumenis at constant densities of O. pratensis eggs, larvae, protonymphs and deutonymphs, and defined the functional response of predator females. The predator consumed significantly more eggs than other prey stages, and displayed a type II functional response on all prey stages. The highest attack rate and shortest handling time were obtained for predators feeding on prey larvae and eggs, respectively. The proportions of prey consumed by G. flumenis were higher at lower densities for all stages of Banks grass mite, implying that G. flumenis should be more effective at suppressing Banks grass mite populations at lower densities. Therefore, in an augmentative release program, G. flumenis would need to be released early in the infestation.     

Effect of pollen,natural prey and factitious prey on the development of <Emphasis Type="Italic">Iphiseius degenerans</Emphasis>

The predatory mite Iphiseius degenerans (Berlese) is commercially available as a biological control agent of thrips and spider mites in greenhouse crops. Developmental duration and immature survival of I. degeneransreared on nine types of food (almond pollen, apple pollen, castor bean pollen, plum pollen, sweet pepper pollen, Tetranychus urticaeKoch, Frankliniella occidentalis(Pergande), Ephestia kuehniella Zeller eggs and Artemia franciscana Kellogg cysts) and on three substrates (Multicel, sweet pepper leaf, and bean leaf) were determined in the laboratory. All experiments were carried out at 25 °C. On Multicel, mean developmental times on pollen ranged from 6.0 to 7.1 days, with the lowest value recorded on almond pollen and the highest on sweet pepper pollen. When reared on castor bean pollen significantly longer developmental times were obtained on a sweet pepper leaf compared to a bean leaf or Multicel. Developmental duration when offered T. urticaeon Multicel ranged between 6.1 and 6.9 days, on a bean leaf development was completed in 8.0 days. The longest developmental times on Multicel were recorded on Ephestia eggs (7.0 days) and on decapsulated Artemia cysts (7.5 days). No development beyond the protonymphal stage occurred in the absence of food or when encapsulated Artemia cysts or thrips larvae were offered on Multicel. On a sweet pepper leaf and a bean leaf, respectively 6.7 and 10.0% of the eggs reached adulthood when thrips larvae were provided as food; developmental times recorded here, were 9.0 and 8.3 days. Overall, immature mortality occurred mainly in the protonymphal stage and ranged from 0.0 to 36.7%. In conclusion, I. degenerans is able to feed on a variety of natural and unnatural foods, but thrips larvae and sweet pepper pollen are unfavourable food for immature development. This could compromise the establishment of this biological control agent when used against thrips in sweet pepper crops.     

Egg hatching response to a range of air humidities for six species of predatory mites

The efficiency of biological control agents is often affected by local conditions such as low relative humidity (r.h.). This is especially true for mites of the family Phytoseiidae, and particularly for their egg stage. A key issue in biological control is thus to assess the drought tolerance of phytoseiid species that are (or that will be) commercialized. In this study, we evaluated the egg hatching response to a humidity range for six species of Phytoseiidae, by assessing the relative air humidity and vapour pressure deficit (VPD) at which 50% of the eggs hatch: r.h.₅₀ and VPD₅₀. Typhlodromus athiasae Porath & Swirskii and Phytoseiulus longipes Evans (Argentinean strain) were the most drought‐tolerant, with a r.h.₅₀ of 43% (VPD₅₀ = 18.2 hPa) and 43% (18.1 hPa), respectively. The most drought‐sensitive species were Amblyseius swirskii (Athias‐Henriot) (63%, 11.4 hPa), Phytoseiulus macropilis (Banks) (69%, 9.8 hPa), and Phytoseiulus persimilis Athias‐Henriot (70%, 9.4 hPa). Neoseiulus idaeus Denmark & Muma and P. longipes (Chilean strain) showed intermediate responses with 49% (16.1 hPa) and 50% (15.9 hPa), respectively. These results were similar to what had been obtained for the same species by other authors. However, unexpected inter‐ and intraspecific differences uncorrelated to climatic conditions of the area of origin were observed. The possibility to localize species and/or populations that could be efficient as biological control agents under dry conditions is discussed.