Dimitris S. Koveos

Effect of Different Pollens on Development, Survivorship and Reproduction of Euseius finlandicus (Acari: Phytoseiidae)

Abstract Development, imaginal survivorship, adult longevity and fecundity of the predatory phytoseiid mite Euseius (Amblyseius) finlandicus Oudemans reared on seven different plant pollens were determined in the laboratory. The rationale behind these experiments was to assess the nutritional value and the possible effect on development and population dynamics of the mite. Mites were kept individually on bean (Phaseolus vulgaris L.) leaf disks at 20 ± 1°C and a photoperiod of 16:8 (L:D) h, with a sufficient quantity of pollen of apple (Malus silvestris M.), pear (Pyrus communis L.), cherry (Prunus avium L.), peach (Prunus persica L.), apricot (Prunus armeniaca L.), walnut (Juglans regia L.), or poppy (Papaver rhoeas L.). Developmental time from neonate larva to adult emergence varied between the different pollens from 6.03 to 6.62 d for females and from 5.46 to 6.14 d for males. Survivorship during immature development varied from 67.2 to 95.9% with the lowest value recorded on peach pollen. The average life span of adult females reared on the different pollens varied from 18.2 to 56.2 d, whereas the respective total fecundity ranged from 2.5 to 46.5 eggs per female. The estimated values of the intrinsic rate of increase (rm) varied from 0.012 to 0.150. The analysis of these results show that cherry, peach, apricot, walnut, and poppy pollens are of higher nutritional value for E. finlandicus than apple and pear pollens and thus may play an important role in the field for sustaining and increasing the predator’s population.

Development, survival and reproduction of Euseius finlandicus (Acari: Phytoseiidae) at different constant temperatures.

Development, survival and reproduction of Euseius finlandicus Oudemans were studied at seven constant temperatures (15, 20, 25, 27, 30, 32 and 34°C) in the laboratory. Within the temperature range tested, developmental period from egg to adult varied from 148 to 360.5 h and 133.7 to 336.5 h for females and males, respectively. The lower thermal threshold for immature development for females and males was 8.9 and 6.4°C, respectively. Survival during immature development exceeded 90% at all the temperatures from 15 to 32°C, but at 34°C an abrupt decline was recorded. Female longevity decreased gradually from 82.7 d at 15°C to 12.2 d at 34°C. The mean generation time ranged from 44.3 d at 15°C to 15.9 d at 32°C. The highest rm value (0.2817) was obtained at 30°C and the lowest at 15°C (0.0976). Temperatures above 30°C had an adverse effect on population increase.

Rapid cold hardening in the olive fruit fly Bactrocera oleae under laboratory and field conditions

A rapid cold hardening response was studied in females and males of the olive fruit fly Bactrocera (Dacus) oleae. When laboratory‐reared females and males were transferred and maintained from the rearing temperature of 24 °C for 2 h to −6.5 °C approximately 5% survived. However, conditioning of both females and males for 2 h at various temperatures from 0 to 10 °C before their exposure for 2 h to −6.5 °C increased survival to 80 to 92%. A similar rapid cold hardening response in both females and males was also induced through gradual cooling of the flies at a rate of approximately 0.4 °C per min. The rapid increase in cold tolerance after prior conditioning of the flies to low temperatures, was rapidly lost when they returned to a higher temperature of 24 °C. In the field, in late February and early March, females and males were capable of a rapid cold hardening response. After exposure to the critical temperature they suffered a high mortality when tested in the afternoon and low mortality early in the morning on consecutive days, probably because of differences in the prevailing field temperatures a few hours before testing. This plasticity of cold tolerance gained through rapid cold hardening may allow the flies to survive during periods of the year with great fluctuation in circadian temperatures.

Development, Survival, and Reproduction of the Predatory Mite Kampimodromus aberrans (Acari: Phytoseiidae) at Different Constant Temperatures

Abstract Development, survival, and reproduction of the predatory mite Kampimodromus aberrans Oudemans were studied at constant temperatures in the range from 15 to 35°C under laboratory conditions. Larval developmental rate for both males and females increased gradually from 15 to 35°C and decreased at higher temperatures. Lactin’s nonlinear model described with adequate accuracy the relationship between developmental rate and temperature. The model predicted that lower and upper threshold temperatures for preimaginal development ranged from 9.8 to 11.8°C and from 37.2 to 39.8°C, respectively. The intrinsic rate of population increase (rm) at the different temperatures ranged from 0.0442 to 0.1575, with the highest value recorded at 25°C. At 33°C a negative rm value was estimated. The rm values determined at different temperatures were fitted to Lactin’s nonlinear model, and the lower and upper threshold and the optimal temperatures for population increase were 10.5, 32.4, and 27.6°C, respectively. These data indicate that K. aberrans may be better adapted to intermediate temperatures around 27°C and, therefore, could be a useful biocontrol agent of spider mites during spring and early summer when such temperatures are prevalent in northern Greece. The results could also be useful in developing a population model for K. aberrans under field conditions.

Functional response of Euseius finlandicus and Amblyseius andersoni to Panonychus ulmi on apple and peach leaves in the laboratory

The functional response of adult females of the predatory mites Euseius (Amblyseius) finlandicus and Amblyseius andersoni to larvae and adult females of the fruit tree red spider mite Panonychus ulmi was determined on apple and peach leaf disks in the laboratory at 25°C and 16:8 (L:D). For adult females of P. ulmi the predation efficiency of E. finlandicus was higher on peach than on apple, whereas that of A. andersoni was higher on apple than on peach. Efficiency of predation on larvae of P. ulmi by either predator did not differ significantly between apple and peach. On both plants, A. andersoni had a higher predation rate than E. finlandicus on larvae of P. ulmi. It is concluded that in the laboratory the host plant has a substantial effect on predation efficiency of A. andersoni and E. finlandicus when they preyed on adults but not when they preyed on larvae of P. ulmi.

Effect of Relative Humidity on Longevity, Ovarian Maturation, and Egg Production in the Olive Fruit Fly (Diptera: Tephritidae)

ABSTRACT The effect of five constant relative humidity (RH) regimes (12, 33, 55, 75, and 94%) on ovarian maturation, adult longevity, and egg production of Bactrocera (Dacus) oleae (Gmelin) (Diptera: Tephritidae) was studied at 25 ± 1°C and a photoperiod of 16:8 (L:D) h under laboratory conditions. The experimental insects developed in the preimaginal stages at 16:8 (L:D) h and 25 ± 1°C, and the adults were maintained in plastic cages in sealed plastic containers with saturated water salt solutions in their base to control RH. In the experiments concerning longevity and egg production, the adults were maintained individually, whereas in those concerning ovarian maturation they were in groups of 10 females and 10 males. Ovarian maturation was much reduced and the number of mature oocytes in the ovaries was very low in 7-d-old females maintained at 12 and 33% RH. By contrast, a high percentage of females of that age maintained at 55, 75, and 94% RHs had mature oocytes in their ovaries. Longevity of adult females, egg production and egg hatch were low at 12% RH. They were significantly higher at 33% RH, and even more so at 55 and 75% RHs but declined at 94% RH. These results could be useful for the mass rearing of B. oleae and for better understanding its population dynamics under field conditions.

Rapid cold hardening in the predatory mite Euseius (Amblyseius) finlandicus (Acari: Phytoseiidae)

A rapid cold hardening response was studied in diapause and non-diapause females of the predatory mite Euseius finlandicus. When laboratory reared diapause and non-diapause females were transferred and maintained from the rearing temperature of 20 degrees C for 2 h to -11.5 degrees C and -10 degrees C, 10 to 20% survived respectively. However, conditioning of diapause females for 4 h at a range of temperatures from 0 to 10 degrees C before their exposure for 2 h to -11.5 degrees C, increased survival to approximately 90%. Similarly, conditioning of non-diapause females for 4 h at 5 degrees C before their exposure for 2 h to -10 degrees C increased survival to 90%. A similar rapid cold hardening response in both diapause and non-diapause females was also induced through gradual cooling of the mites, at a rate of approximately 0.4 degrees C per min. The rapid increase in cold tolerance after prior conditioning of the mites to low temperatures, was rapidly lost when they returned to a higher temperature of 20 degrees C. Rapid cold hardening extended the survival time of diapause and non-diapause females at sub-zero temperatures. The cost of rapid cold hardening in reproductive potential after diapause termination was negligible. In non-diapause females, however, the increase in cold tolerance gained through gradual cooling could not prevent cold shock injuries, as both fecundity and survival were reduced.

Threshold Temperature for Post-Diapause Development and Degree-Days to Hatching of Winter Eggs of the European Red Mite (Acari: Tetranychidae) in Northern Greece

Abstract The threshold temperature for postdiapause development in overwintering eggs of the European red mite, Panonychus ulmi (Koch), was determined after exposing the eggs to various constant temperatures (5, 10, 15, 20, and 25°C) in the laboratory. The mean number of days to 50% hatch in each temperature was >120, 44.5, 22.0, 14.5, and 8.1 d, respectively. From the regression of postdiapause developmental rate to temperature, it was estimated that 50% of egg hatch coincides with the accumulation of 154.6 degree-days (DD) above the threshold of 7.4°C. In the field (1991 and 1993–1996), 50% egg hatch occurred from the end of March to 20 April after the accumulation of a mean sum of 129.4 ± 4.5 DD above the threshold of 7.4°C from 10 February onward. The starting date of 10 February for heat accumulation was chosen because earlier experiments had shown that diapause is terminated in 50% of the eggs in the first half of February. Using the theoretical sum of 154.6 DD, the predicted dates for 50% egg hatch deviated from field observations by an average of 3.7 ± 0.5 d over the 5 yr of experiments.

Effect of cold exposure and photoperiod on diapause termination of the predatory mite Euseius finlandicus (Acari : Phytoseiidae)

Abstract The effect of cold storage and photoperiod on diapause termination of the predatory mite Euseius finlandicus was studied under laboratory conditions. Females in diapause that developed under a short-day photoperiod of L:D 8:16 h and 20°C were exposed for 1–13 wk to 5°C and subsequently maintained under L:D 8:16 h and 20°C, after which the percentage of females terminating diapause was recorded. After 1–4 wk at 5°C, the number of days required for diapause termination in 50% of females (TA50) was similar to that of the control mites maintained continuously at L:D 8:16 h and 20°C. This indicates that cold is not a prerequisite for the completion of diapause development. Furthermore, when mites were maintained for longer periods (7, 10, or 13 wk) at 5°C, TA50 was significantly longer than in the control mites. This may indicate an adverse effect of cold storage on the completion of diapause development or on postdiapause development. However, the longer exposures to cold resulted in synchronous diapause termination. When diapause females were maintained under a series of different photoperiods and 20°C without previous cold exposure, diapause was terminated rapidly under the photoperiods of L:D 16:8, 14:10, and 13:11 h. In contrast, under the shorter-day photoperiods of LD 8:16, 10:14, and 12:12 h, diapause was maintained and eventually ended spontaneously after a long period of time. These results may be useful for the long-term storage of this predatory mite, which could be required for use in biological control programs.

Cold Hardiness Characteristics in a Strain of the Predatory Mite Euseius ( Amblyseius ) finlandicus (Acari: Phytoseiidae) from Northern Greece

Abstract The supercooling points (SCP) of immature stages and adults as well as survival of adult females after exposure to subzero temperatures were studied in a strain of the predatory mite Euseius finlandicus (Oudemans) from northern Greece. The mean SCP of eggs was −27.6°C. The mean SCPs of different immature stages fed on pollens of Papaver rhoeas L. or Typha sp. enriched with β-carotene were similar and varied from −21.1 to −24.7°C. The mean SCPs of diapause females acclimated for 2 wk at 5°C or not acclimated, nondiapause females and males fed on pollens of P. rhoeas and Typha sp. were similar and varied from −22 to −24.3°C. When groups of diapause females were exposed temporarily to different subzero temperatures, the temperature-mortality curve followed the distribution of the SCPs, which indicates that the SCP is the lower limit of survival. More than 80% of the diapause females died when exposed for 20 min to −15°C, a temperature well above the SCP which indicates that they suffered prefreeze mortality. They survived considerably longer durations of exposure to −15°C after a prior acclimation for 2 wk at different low temperatures. After certain acclimation treatments, diapause females that survived exposure to −15°C laid a similar number of viable eggs as those not exposed to subzero temperatures, which indicates that cold stress may not affect fecundity.