G.D. Broufas

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.

Effect of heat stress on survival and reproduction of the olive fruit fly Bactocera (Dacus) oleae

The olive fruit fly Bactrocera (Dacus) oleae Gmelin is a major olive pest in Greece and other Mediterranean countries. Its population density and respective olive infestation is usually low in many areas of northern Greece during summer months. To some extent, this may be due to the prevailing high temperature and low relative humidity conditions. In the present work the effects of short term exposure to high temperatures on the survival and egg production of B. oleae pre‐imaginal stages and adults were studied under laboratory conditions. Different larval instars within infested green olive fruits, adults and pupae and were exposed for 2 h to a series of different high constant temperatures ranging from 34 to 42°C. Subsequently, survival percentages of pre‐imaginal stages and adults as well as the number of eggs laid by females previously exposed to high temperatures were determined. At temperatures up to 38°C high survival percentages of larvae and adults were observed, whereas pupae displayed a relatively increased heat tolerance up to 40°C. Female longevity and egg production were substantially reduced after heat stress. Prior acclimation at 33°C for 1 and 3 days resulted in increased adult survival following heat stress. We discuss the results with respect to the ability of the fly to survive and reproduce under high summer temperatures.

Effect of Prey Availability on Development and Reproduction of the Predatory Lacewing Dichochrysa prasina (Neuroptera: Chrysopidae)

ABSTRACT Preimaginal development and reproduction of the predatory lacewing Dichochrysa prasina Burmeister (Neuroptera: Chrysopidae) when its larvae had access at different nymphal numbers of the aphid Myzus persicae (Sulzer) (Hemiptera: Aphididae) were studied under laboratory conditions at 25 ± 1°C and a photoperiod of 16:8 (L:D) h. Preimaginal development decreased from 46.0 to 31.6 d for females and from 41.4 to 31.5 d for males, with an increase in the number of available aphids from five to 110 nymphs of M. persicae per larva of D. prasina. Preimaginal survival ranged from 55.8% at the lowest to 86.0% at the highest aphid numbers. Prey consumption by D. prasina larvae increased with an increase in aphid numbers, with the third instar being the most voracious. Longevity of D. prasina females ranged from 38.2 to 54.5 d, and total egg production ranged from 59.2 to 369.7 eggs per female at the lowest and highest prey numbers tested, respectively. The estimated values for the intrinsic rate of increase (rm) were affected by prey availability and the highest rm (0.0838) was recorded at the highest prey number tested. Based on the results of the current study, it is likely that D. prasina can develop and reproduce either at high or low density aphid populations in the field, and effectively suppress them.

Development and Reproduction of the Lacewings Dichochrysa flavifrons and Dichochrysa zelleri (Neuroptera: Chrysopidae) Fed on Two Prey Species

ABSTRACT The lacewings Dichochrysa flavifrons (Brauer) and Dichochrysa zelleri (Schneider) (Neuroptera: Chrysopidae) are considered as important biological control agents, and mass rearing is a prerequisite for their use in biological control programs. We evaluated the effect of Ephestia kuehniella Zeller eggs that are widely used for mass rearing other chrysopids and the nymphs of the aphid Acyrthosiphon pisum (Harris) on the development and reproduction of D. flavifrons and D. zelleri at 25°C and a photoperiod of 16:8 (L:D) h. Preimaginal development of D. flavifrons and D. zelleri was significantly shorter when their larvae were fed on E. kuehniella eggs than on A. pisum nymphs. In D. flavifrons, the intrinsic rate of increase (rm) was higher when larvae were fed on E. kuehniella eggs than on A. pisum nymphs. By contrast, in D. zelleri rm was higher when larvae were fed on A. pisum nymphs than on E. kuehniella eggs. The differences in development and reproduction among the two tested species when their larvae were fed on different prey could be of importance for their mass rearing and use in biological control.