Invertebrate predation of 15N-marked prey in semi-field wheat enclosures

One of the most famous examples of successful, classical biological control in Japan is the introduction of the parasitoids Coccobius fulvus and Aphytis yanonensis against the citrus pest arrowhead scale Unaspis yanonensis. Together, they comprise a host‐parasitoid system that has been demonstrated to be stable. To test the conventional theory that successful biological control of pests occurs through the establishment of a low stable equilibrium, brought about by the density‐dependent responses of natural enemies to the pest species, sampling was carried out at five sites in the field during 2000 and 2001 to examine the relationship between the rate of parasitism by C. fulvus and the density of its host. The data were analysed using three statistical techniques at nine spatial scales. Contrary to conventional theoretical predictions, each method of analysis detected very little density‐dependence at any spatial level in this study. Parasitoid aggregations independent of host density were not sufficient to stabilise host–parasitoid interactions. Our results suggest that neither spatial density‐dependent nor density‐independent parasitism is necessary for successful biological control, or for the stability of the host–parasitoid system. We propose an alternative mechanism: a spatial refuge induced by parasitoid introduction may stabilise a system.     

Functional response and progeny production of the Madeira mealybug parasitoid, Anagyrus sp. nov. nr. sinope: The effects of host and parasitoid densities

We tested the hypothesis that control of an herbivorous pest would be improved by providing floral resources for adult natural enemies. The herbivore was euonymus scale, Unaspis euonymi (Comstock) (Homoptera: Diaspididae), a serious pest of woody ornamental plants. The experimental landscape consisted of 3 × 3 m plots, each containing a central bed of Euonymus fortunei (Turcz.) that was infested with the scale. Floral resource plants were cultivars of four species that overlapped in bloom periods to provide a continuous supply of floral resources during summer: Trifolium repens L., Euphorbia epithymoides L., Coreopsis verticillata L. var. ‘Moonbeam,’ and Solidago canadensis L. var. ‘Golden Baby.’ Plots contained either low or high densities of all four species, or no resource plants. Densities of euonymus scale were typically lower in plots containing resource plants than in plots without them. Parasitism by Encarsia citrina (Craw.) (Hymenoptera: Aphelinidae) was rarely influenced by the experimental treatments, flower biomass, whole-plant biomass, or scale density, but in some cases was inversely correlated with density of scales within a generation and in the subsequent generation. Parasitism occasionally reduced densities of scales in plots containing resource plants, but this effect apparently was related to vegetative, not floral qualities of plants. A steady increase in parasitism rate over the three-year course of the experiment across the entire landscape was associated with decreasing density of scales, suggesting a numerical response by the parasitoid population. These findings suggest that the parasitoid is capable of effectively controlling euonymus scale in ornamental landscapes where environmental conditions are favorable.     

PREDATION OF THE LADYBEETLE CHILOCORUS KUWANAE ON THE SCALE UNASPIS YANONENSIS

Abstract The prey consumption of ovipositing female adults of the ladybeetle Chilocorus kuwanae on the scale Unaspis yanonensis was found to be significantly greater than that of the male adults. At 25°C one female adult ladybeetle, on average, would consume 42. 7 female scale adult per day while one male adult only destroyed 22. 3 female scale adults. However, after a deprivation of the prey for 48 h, this difference was eliminated. A C. kuwanae female adult had to prey on at least 15 U. vanonensis female adults in order to lay eggs. The funcional responses of the beetle adults to densities of different stages of the scale followed Holling's type 1. The functional responses to female scale adults indicated that the maximum prey consumption went up with the increase in temperature from 16°C to 35°C, and dropped sharply at 37°C. However, temperature did not alter the type of the functional response. Rased on the predation of C. kuwanae adults on U. yanonensis female adults, the minimum critical, optimal and maximum critical temperatures for their attack were estimated to be 10. 6°C, 31. 5°C and 38. 2°C respectively. The increase in predation space or in predator density could result in a reduction in the attack rat-e, but with the increase of predator density, the effect of predation space became much smaller. C. kuwanae adults preferred male pupae to other stages of the scale, and their preference for various stages of the prey was in the order of male pupae, 2nd-instar male nymphs, 2nd-instar female nymphs, adult females and kinstar nymphs.     

A Simulation model for the arrowhead scale (Hemiptera: Diaspididae) population dynamics on citrus trees in relation to pest-management programs

1. A mathematical model was constructed describing population dynamics of the arrowhead scale, Unaspis yanonensis Kuwana. The population occurrence patterns simulated by the model from 1971 to 1976 were relatively consistent with the actual findings in the field.
2. The effects of control tactics for this pest were examined on the basis of the model.
3. Effective timing of insecticide (petroleum oil and organophosphorous insecticide) application was indicated to be 40 days after the initial appearance of 1st-instar nymphs in both the 1st and 2nd generations of the host.
4. The number of overwintering adult females in May of the next year (i.e., the starting point of the next year's population) decreased linearly with the increment in the degree of insecticide coverage. The pest populations were expected to be kept to low densities by petroleum oil sprays alone for the 1st generation when overall, complete coverage was accomplished.
5. Examination of the effects of two introduced parasitoids, Aphytis yanonensis and Coccobius fulvus, showed that they were able to control the scale population by themselves when more than 70% parasitism was achieved. When petroleum oil was applied to overwintering adults (termed winter petroleum oil) at the degree of coverage of 0.8, host populations were reduced by ca. 60% parasitism. When the winter petroleum oil was combined either with additional petroleum oil 40 days after the initial appearance of 1st-instar nymphs of the 1st generation or with an organophosphorous insecticide 40 days after the initial appearance of 1st-instar nymphs of the 2nd generation (degree of coverage=0.8 in each case), 40% parasitism led the reduction of the pest population.
6. The most desirable control program was considered to be one in which winter petroleum oil was used every year and additional petroleum oil or an organophosphorous insecticide was also used in those years when host density was high.

     

寄生柑桔矢尖蚧的跳小蜂一新种：膜翅目：跳小蜂科

本文记述盾蚧跳小蜂ＣｏｃｃｉｄｅｎｃｙｒｔｕｓＡｓｈｍｅａｄ１新种,即长尾 盾蚧跳小蜂     

Fitness cost of parasitoid avoidance behavior in the arrowhead scale, Unaspis yanonensis Kuwana

We examined trade‐offs between fitness components and the parasitoid avoidance behavior of the arrowhead scale, Unaspis yanonensis Kuwana (Homoptera: Diaspididae). We examined the performance of two settling modes: singleton and double settling with the burrower under the burrowee. Each of these modes differs in vulnerability to parasitism by Aphytis yanonensis DeBach et Rosen and Coccobius fulvus Compere et Annecke (Hymenoptera: Aphelinidae), and performance. Field and laboratory observations revealed smaller body size and lower parasitism of burrower scales, while both singletons and burrowees showed the opposite tendency (larger body size and a greater parasitism rate). Laboratory observations under parasitoid‐free conditions revealed greater mortality and reduced growth rate for simulated burrowers than for singletons during the 40‐day nymphal period. This suggests that competition for food resources reduces performance. The results also suggest trade‐offs between parasitoid avoidance and resource acquisition ability in U. yanonensis. The trade‐offs also explain our previous findings, that introduction of the parasitoids increased the proportion of burrowers, but that within seven years equilibrium was reached at fairly low levels (ca. 5%) in the field, even under intense parasitism.     

A ten-year study of population dynamics of citrus pests in the pesticide-reduced orchard

To determine the effectiveness of a pest management system that uses pesticides at a low level, we censused populations of seven insect pests and three plant diseases from 1980 to 1989 in a citrus orchard which was managed with a pesticide-reduced and pesticide-free protocols, in Wakayama Prefecture, Japan. In the orchard, we controlled the pests solely by spraying petroleum oil once a year from 1980 to 1985, by not spraying insecticide in 1986, and spraying only germicide in 1987. The arrowhead scale population remained much lower level at which citrus trees begin to wither when petroleum oil was sprayed, whereas it rapidly increased and began to wither trees during the years without spraying petroleum oil. The Indian wax scale population rapidly increased only during a 2-year period and then declined. Although the infection level of the sooty mold was unusually high on the trees where the density of the scale was high, this pathogen did little damage to citrus trees. The population of the red wax scale gradually increased throughout the census period but did not reach the level at which citrus trees begin to be damaged. Other pests also caused negligible damages to citrus trees. The results indicated that the pesticide-reduced pest management system which was proposed by Inoue and Ohgushi (1976, 1977) is valid for the prevention of the outbreak of the arrowhead scale, and that is has the sufficient control efficiency for the other pests in citrus orchards.     

Biological control by two exotic parasitoids: eight-year population dynamics and life tables of the arrowhead scale

To determine the process of regulation of Unaspis yanonensis (Kuwana) (Hemiptera: Diaspididae) by the two introduced parasitoids, Aphytis yanonensis DeBach et Rosen and Coccobius fulvus (Compere et Annecke) (Hymenoptera: Aphelinidae), the temporal changes in the population density of U. yanonensis as well as the parasitism rates were monitored for eight years before and after the release of the two parasitoids in a Satsuma mandarin orange (Citrus unshiu Marc. (Rutaceae)) orchard. From 2–4 years after the release, the parasitism rate by C. fulvus gradually increased, eventually reaching 70%, while that by A. yanonensis showed a weak increase, remaining under 12%. During this period, the host density decreased to about 1/100 of the initial density. After the drastic decrease, the host density remained under 1/60 of the level previous to the release for at least 2 years with the populations of both parasitoids persisting. To estimate the ability of the two parasitoids to regulate the populations of U. yanonensis, life tables of U. yanonensis under natural conditions and predator/parasitoid-exclusion (bagged) conditions were compared. It was demonstrated that C. fulvus and A. yanonensis impose about 70% mortality rate on the host at mature adult stages and about 30% on the host at immature adult stages. The results have strongly confirmed the high capability of the two parasitoids as biological control agents for U. yanonensis, which was suggested by earlier studies. However, contrary to those studies, the present study did not support the complementarity of the two parasitoids in regulating the host population, suggesting that the effectiveness of C. fulvus alone in regulating the host population at low levels.     

Rapid change in the settling behavior of the arrowhead scale Unaspis yanonensis as an avoidance mechanism against introduced parasitoids, Aphytis yanonensis and Coccobius fulvus

Abstract Parasitoids are thought to exert immense selection pressures that shape the traits of herbivores. We examined whether two species of parasitoid wasps, Aphytis yanonensis DeBach et Rosen and Coccobius fulvus Compere et Annecke (Hymenoptera: Aphelinidae), affect the settling behavior of the arrowhead scale Unaspis yanonensis Kuwana (Hemiptera: Diaspididae), in order to demonstrate the evolution of antiparasitism behavior of herbivores using parasitoids in the field. We used the following five methods: a comparison of parasitism risk in different settling behaviors‐parasitoid introduction into a parasitoid‐free population; a comparison of the settling behavior between parasitoid‐present and parasitoid‐free populations; a common garden experiment, in which scales were transferred from parasitoid‐present and parasitoid‐free populations into the same garden; and a laboratory observation of the settling behavior of the first instars derived from the two population categories. Both parasitoids were introduced into a parasitoid‐free population in Wakayama in 1987, and the settling mode of the scales was examined in 1987, 1994, and 1995. The introduction of parasitoids modified the scale‐settling mode so that more crawlers settled under another scale (called burrowing), which was consistent with the results observed in parasitoid‐present (including South China) and parasitoid‐free populations. Moreover, only the burrowing scale exhibited a lower parasitism rate compared to scales settling singly and being burrowed. The common garden experiment demonstrated that scales introduced from the parasitoid‐present population had a greater proportion of burrowers than the parasitoid‐free population, even in the same field cage under parasitoid‐free conditions. Laboratory observations demonstrated that the population difference in parasitism rate was principally due to intrinsic differences in the settling behavior of nymphs; some first‐instar nymphs derived from the parasitoid‐present population burrowed under another scale settled. These results strongly suggest that the natural selection pressure imposed by the parasitoids modified the settling behavior of the arrowhead scale.