Yvonne Maria Van Houten

HOW PLANTS BENEFIT FROM PROVIDING FOOD TO PREDATORS EVEN WHEN IT IS ALSO EDIBLE TO HERBIVORES

It is well established that plants provide alternative foods to predators of herbivorous arthropods. This provision may facilitate protection against herbivory. However, plants often cannot prevent other organisms from utilizing these foods as well. There are many examples of herbivorous arthropods that can feed on plant-provided foods such as extrafloral nectar and pollen. The question therefore arises whether individual plants still gain protection when not only the predators, but also the herbivores, can feed on these foods. We investigated this question using a mathematical model and experiments that assessed the impact of supplementary pollen on the dynamics of predatory mites (Iphiseius degenerans (Berlese)) and herbivorous thrips (Frankliniella occidentalis (Pergande)), two arthropods capable of using pollen for reproduction. Replicated greenhouse experiments showed that addition of pollen every two weeks to one young mature leaf of a male-sterile cucumber plant increased predator population growth...

Control of Western Flower Thrips on Sweet Pepper in Winter with Amblyseius cucumeris (Oudemans) and A. degenerans Berlese

A non-diapause strain of the predatory mite, Amblyseius cucumeris (Oudemans), and a strain of the drought-resistant, non-diapause species, A. degenerans Berlese, were evaluated as biological control agents of western flower thrips (WFT), on greenhouse-grown sweet peppers in winter. Both mite species established on the crop when released in late January. A. degenerans had a greater impact on WFT populations than A. cucumeris, and specific characteristics enabling successful control are discussed.

Photoperiodic control of adult diapause in the predacious mite, Amblyseius potentillae: repeated diapause induction and termination

ABSTRACT. Photoperiodic control of facultative reproductive diapause was examined in females of the phytoseiid mite, Amblyseius potentillae (Garman). Full diapause was induced by rearing the mites from egg to adult under short‐day photoperiods. Egg‐laying females, however, which had experienced a long‐day photoperiodic regime during pre‐imaginal development, could still be induced to enter diapause when they were transferred to a short‐day regime. Diapause development proceeded slowly under a short‐day photoperiod, but was accelerated under long days. During diapause development under short days the photoperiodic sensitivity of the females diminished gradually and ultimately disappeared completely. However, after completion of diapause, sensitivity to photo‐period reappeared. A second diapause could be induced in post‐diapause females under short‐day photoperiods and completed again under long‐day photoperiods. These results show that A. potentillae remains sensitive to diapause‐inducing and diapause‐averting daylengths during the adult stage and that a second diapause may be induced after completion of the first one.

Effects of photoperiod, temperature, food and relative humidity on the induction of diapause in the predatory miteAmblyseius potentillae

Aspects of the induction of diapause were studied in a Dutch strain of the phytoseiid miteAmblyseius potentillae. The photoperiodic response curve was of the long-day type, with a sharply defined critical daylength of 14.5 h. Critical daylength varied only little at temperatures between 15.0 and 22.5°C.All post-embryonic and possibly even late-embryonic stages of development were found to be sensitive to photoperiod; sensitivity appeared to be maximal during the protonymphal stage.It is shown that β-carotene is necessary for some early step in the physiological mechanism of photoperiodic induction, and not (or not exclusively) for the expression of the diapause response.Two points of sensitivity to light could be demonstrated in the nights ofl∶d 13∶11 andl∶d 12∶12 long-night regimes, using 1-h night interruptions. These results are similar to those obtained in lightbreak experiments with spider mites and insects. However, no effect was found with light interruptions applied during the dark phase of anl∶d 10∶14 long-night regime.In resonance experiments with a constant photophase (12 h) and a variable scotophase, a weak rhythmic response was found at 22.5°C; at 19.0°C this effect was completely absent.The relative humidity experienced by the mites during diapause induction as well as during diapause development influenced the rate of diapause completion under long days (l∶d 16∶8). Diapause duration appeared to be shortest when the mites experienced low relative humidity (35±5%) during diapause induction and high relative humidity (75±5%) during diapause termination, and longest under the reverse conditions.

Development of an economic rearing and transport system for an arid-adapted strain of the predatory mite, Neoseiulus californicus, for spider mite control

Neoseiulus californicus (McGregor) is a relatively effective phytoseiid predator against spider mites reported from the Americas (North and South), Africa, the Mediterranean basin, and Japan. This study was a collaborative effort to identify and mass-rear a strain of N. californicus that is more efficacious under arid conditions than the standard commercial strain from California (USA). N. californicus strains were collected in arid areas worldwide. Discriminant analysis performed with 30 morphological variables allowed for their separation. The performance of these strains under arid conditions and on selected host plants was evaluated in laboratory and semi-field trials. Development and survival of eggs and juveniles differed among strains and humidities. Female performance (survival, oviposition) was influenced by strain but not by humidity. The Californian reference strain was superior to all others, when considering both adaptation to dry conditions and power of population increase at low humidities. Whole potted plant trials (cucumber, strawberry, and pepper) confirmed this result. Field trials were conducted to compare this new product to the standard commercial strain of Phytoseiulus persimilis Athias-Henriot. To identify possible influence of symbiotic bacteria on strains of N. californicus general primers for the 16S rDNA gene were used in a PCR. Among other bacteria, a Spiroplasma, closely related to the one found in various arthropods, was detected in two strains, and it was further characterized. No influence on the hosts developmental time, fecundity, and sex ratio could be detected. To provide this product at an affordable cost for European growers an economic rearing and delivery system for N. californicus was developed and its marketing potential in Europe and neighboring countries was estimated.