A.J.M. Loomans

Evaluation of an improved method for mass-rearing of thrips and a thrips parasitoid

Improved laboratory methods are described in detail for mass rearing of various thrips species, such as Frankliniella occidentalis, Frankliniella intonsa, Thrips palmi, Thrips tabaci (Thysanoptera: Thripidae) and a thrips parasitoid, Ceranisus menes (Hymenoptera: Eulophidae), using various foods. In one method, plant pollen and honey solution are used as food sources. In a second method, germinated broad bean seeds are used. Eggs, produced in large numbers in water, are collected by a suction funnel onto a filter paper and incubated in a Petri dish. Large numbers of larvae that hatch are collected by using food traps (plant pollen). Larvae can be reared on pollen or on germinated broad bean seeds until adult emergence without additional water and food. This method has been found useful for producing even‐aged thrips at different densities (up to 500 larvae in a cage of 80 mm diameter) with relatively low mortality rates. Evaluation of this rearing method for F. intonsa, shows that during 2 weeks at 20 °C per 100 females more than 4000 females could be produced in the next generation. About 5 min per day is required to achieve this productivity of mass production. The method is also suitable for producing large numbers of the solitary endoparasitoid of thrips larvae, C. menes.

Inter- and Intraspecific Effects of Volatile and Nonvolatile Sex Pheromones on Males, Mating Behavior, and Hybridization in Eretmocerus mundus and E. eremicus (Hymenoptera: Aphelinidae)

Eretmocerus species (Hym. Aphelinidae) are solitary parasitoids of Bemisia tabaci (Gennadius). Mate finding and mating behavior of two species, E. mundus and E. eremicus, were studied under laboratory conditions. We used three populations of Eretmocerus: typical arrhenotokous populations of E. eremicus (from USA) and E. mundus (from Spain), and an atypical thelytokous population of E. mundus (from Australia). We studied the intra- and interspecific responses of males to volatile and nonvolatile components of the female sex pheromones, mating behavior, and hybridization between populations and species. In both arrhenotokous populations, males reacted to volatile pheromones by walking toward conspecific virgin females. Males also reacted to nonvolatile pheromones by spending more time on and around patches on leaves of poinsettia plants that had been exposed to virgin females. Males of E. eremicus showed the same reaction to the nonvolatile sex pheromone of E. mundus females, but E. mundus males did not show any reaction to the nonvolatile sex pheromone of E. eremicus. There was no response of males of both species to thelytokous females of E. mundus. In both species three phases were distinguished in the mating behavior: premating, mating, and postmating. The duration of the phases differed between the three populations. Successful copulation between the two Eretmocerus species did not occur. In contrast, we recorded some successful copulations between Australian males and Spanish females of E. mundus, but they did not produce any hybrid females.

Hyperparasitism behaviour of the autoparasitoid Encarsia tricolor on two secondary host species

Hyperparasitism by virgin female Encarsia tricolor was studied by direct observation of its behaviour when contacting two secondary host species (Encarsia formosa and E. tricolor) at different host stages (first and second larval stage, third larval stage, and pupal stage). The searching and hyperparasitism behavioural sequence of E. tricolor was independent of the host stage of the whitefly (Aleyrodes proletella), and was similar to several related primary parasitoid species. In experiments with equal numbers of secondary hosts, encounter frequencies were equal for both secondary host species in all developmental stages observed. However, rates of hyperparastism were different according to host stage and host species. Hosts in the late larval stages were most preferred for hyperparasitization and the heterospecific E. formosa was more preferred as a secondary host than the conspecific, E. tricolor, in particular from the prepupal stage onwards. The window of vulnerability, i.e., the duration of the period in which a secondary host is susceptible to hyperparasitism, was largely determined by the occurrence and rate of melanization after the onset of pupation. The duration of a successful hyperparasitization event was longer than one that failed. Superparasitism occurred only once in all cases. The potential effect of autoparasitoids on biological control programs and the consequences for selection and release of an effective, yet ecologically safe agent are discussed.

Host-Parasite Interaction between Frankliniella intonsa , Western Flower Thrips and Ceranisus menes (Hymenoptera: Eulophidae): Development and Reproduction

The life history of the endoparasitoid, Ceranisus menes (Walker) (Hymenoptera: Eulophidae) was studied in the laboratory on Frankliniella intonsa and western flower thrips (WFT). Parasitoid development and reproductive capacity depended on temperature. Development is synchronized with larval development of the host and is faster on WFT than on F. intonsa. There is a marked variation in pupal duration of C. menes at 20 and 25°C. Average longevity of C. menes did not differ between WFT and F. intonsa at 25°C. Fecundity was 2.5 times as high with WFT as hosts than with F. intonsa. The intrinsic rate of increase (r m ) of C. menes on WFT was higher than that on F. intonsa at both temperatures, but was lower than those of the thrips hosts. It is suggested that multiple releases will be needed to control F. intonsa or WFT outbreaks.

Ceranisus menes (Hymenoptera: Eulophidae) for Control of Western Flower Thrips: Biology and Behavior

The potential of Ceranisus menes (Walker) for control of western flower thrips (WFT) was evaluated in the laboratory. A method is described for rearing thrips and parasitoids, using bean pods as host plants and different Frankliniella species (schultzei, WFT) as hosts. Strains collected worldwide, differed in biology and behavior, according to their phenotypic appearance (color form) and geographical origin. Analysis of behavior showed that host acceptance is related to stage, size and movement of the host larva. As size increased, fewer were attacked and parasitized successfully. First instar WFT were preferred, and yellow strains of the wasp were more effective than brown ones. Yellow types produced more offspring but showed a larger variation in developmental time than brown types.