Influence of host size on the clutch size and developmental success of the gregarious ectoparasitoid Eulophus pennicornis (Nees) (Hymenoptera: Eulophidae) [corrected] attacking larvae of the tomato moth Lacanobia oleracea (L.) (Lepidoptera: Noctuidae).

The relationship between clutch size, host size and progeny survival in the gregarious ectoparasitoid Eulophus pennicornis was investigated in a number of scenarios. When naive parasitoids were exposed singly to Lacanobia oleracea hosts, clutch size was strongly correlated with the size of the host. However, survival of parasitoid offspring was negatively affected by the size of the host such that, in larger hosts, greater wasp larval and pupal mortality was recorded. As a result, no gain in realised fecundity was achieved through parasitizing L. oleracea larvae of mass >0.4 g over hosts of mass between 0.2-0.3 g. When exposed to populations of mixed stadium hosts (larvae in the fourth, fifth and sixth instars) during the entire lifespan of the wasp, host size and clutch size were correlated in early ovipositions (first three ovipositions). However, as the wasps aged, the relationship was much less apparent. When the parasitoid was restricted to foraging upon populations of sixth instar hosts only, no relationship between host size and clutch size was apparent. Exposure of the parasitoid to mixed and fixed stadium host populations showed that final (sixth) stadium hosts were the most frequently parasitized (ca. 96% of parasitized hosts) and that the average numbers of eggs laid per wasp, and the number of hosts parasitized, was significantly lower when the parasitoid was provided with fourth or fifth instar hosts only. The results indicate that the reproductive success of E. pennicornis does not increase with increasing host size or greater resource availability above a certain threshold, and that the physiological status of the host at the time of parasitism is the governing factor determining oviposition decisions and parasitoid survival. We conclude that E. pennicornis has been selected to preferentially utilize those hosts that maximize progeny survival and to adapt clutch size to the size of such hosts. We hypothesize that the major driver leading to the evolution of this strategy is the ability of the parasitoid to physiologically regulate the host.

Effect of dietary cowpea trypsin inhibitor (CpTI) on the growth and development of the tomato moth Lacanobia oleracea (Lepidoptera: Noctuidae) and on the success of the gregarious ectoparasitoid Eulophus pennicornis (Hymenoptera: Eulophidae).

Cowpea trypsin inhibitor (CpTI) was shown to have a deleterious effect on the growth and development of larvae of the tomato moth, Lacanobia oleracea, when incorporated in artificial diet (2.0% of soluble protein) and expressed in transgenic potato leaf (up to 1.0% of soluble protein). The effect of CpTI on parasitism of L oleracea by the ectoparasitoid Eulophus pennicornis was investigated. The parasitic success of the wasp was reduced by the presence of CpTI in the diet of the host and, in the case of transgenic potato leaves expressing the transgene protein, was collated with the length of time the host fed on the diet prior to parasitism. In all cases the proportion of hosts parasitised when fed CpTI-containing diets was reduced when compared with controls, although these differences were only significant when hosts were fed from the third instar on the transgenic potato leaves. Parasitoid progeny that developed on L oleracea reared on CpTI-containing diets, however, were not adversely affected. These results show that, whilst expression of CpTI in transgenic potato plants confers resistance to the lepidopterous pest L oleracea, adverse effects on the ability of the ectoparasitoid E pennicornis to parasitise this moth species successfully may also occur. These results are discussed in relation to the potential impact of transgenic crops on beneficial biological control agents.

Transgenic GNA expressing potato plants augment the beneficial biocontrol of Lacanobia oleracea (Lepidoptera; Noctuidae) by the parasitoid Eulophus pennicornis (Hymenoptera; Eulophidae).

The effect of expressing the gene encoding snowdrop lectin (Galanthus nivalis agglutinin, GNA) in transgenic potato plants, on parasitism of the phytophagous insect pest Lacanobia oleracea by the gregarious ectoparasitoid Eulophus pennicornis, was investigated in glasshouse trials. Expression of GNA (approx. 1.0% total soluble protein) by transgenic plants significantly reduced the level of pest damage, thus confirming previous studies. Furthermore, the presence of the parasitoid significantly reduced the levels of damage incurred either by the transgenic or control plants when compared to those plants grown in the absence of the parasitoid. For the GNA expressing plants the presence of the parasitoid resulted in further reductions (ca. 21%) in the level of damage caused by the pest species. The ability of the wasp to parasitise and subsequently develop on the pest larvae was not altered by the presence of GNA in the diet of the host. E. pennicornis progeny that developed on L. oleracea reared on GNA expressing plants showed no significant alteration in fecundity when compared with wasps that had developed on hosts fed on control potato plants, although mean size and longevity of female parasitoids was significantly reduced. The number of F2 progeny produced by parasitoids derived from hosts fed on GNA expressing plants was not significantly different to those produced by parasitoids from hosts fed control plants. Results from the present study demonstrate that the use of transgenic plants expressing insecticidal proteins can be compatible with the deployment of beneficial insects and that the two factors may interact in a positive manner.

The role of allatostatic and allatotropic neuropeptides in the regulation of juvenile hormone biosynthesis in Lacanobia oleracea (Lepidoptera: Noctuidae).

In the sphinghid moth Manduca sexta, two allatoactive neuropeptides appear to be responsible for regulating juvenile hormone (JH) production by the corpora allata (CA). These peptides (M. sexta allatostatin, Mas-AS, and M. sexta allatotropin, Mas-AT) respectively inhibit and stimulate in vitro JH biosynthesis by CA in this insect. However, although Mas-AS inhibits CA in both larval and adult insects, Mas-AT is active only in adult M. sexta. The situation in other lepidopteran species is less clear-cut and, although both peptides have been detected (usually by immunologic and/or molecular techniques) in several other moths (including noctuids), their function as regulators of JH production remains uncertain. In the tomato moth Lacanobia oleracea (Lepidoptera: Noctuidae), we have previously demonstrated the occurrence of Mas-AS and/or Mas-AT in extracts of CA, brain and other organs, and have shown that both peptides are present in larval and adult forms. However, in L. oleracea, although Mas-AS inhibits larval and adult CA in vitro, it does so only at relatively high concentrations, and to a maximum of only approximately 70%. By contrast, Mas-AT (which is also present in larval and adult L. oleracea) stimulates larval and adult CA, but is substantially more potent ( approximately 100 fold) than the allatostatin. In this paper we present the results of paired, concurrent measurements (using ELISA) of levels of Mas-AS and Mas-AT in brains, CA and hemolymph (plasma and hemocytes) of L. oleracea at times when there are marked changes in JH titers. We also present data on the in vitro rates of JH biosynthesis by isolated CA, and on hemolymph JH esterase activity measured at the same critical developmental times, and discuss all of these data in relation to the putative allatoregulatory roles of the M. sexta allatotropic and allatostatic neuropeptides in L. oleracea.

The biology of Meteorus gyrator (Hymenoptera: Braconidae), a solitary endoparasitoid of the tomato moth, Lacanobia oleracea (Lepidoptera: Noctuidae).

There is a need to identify potential biological control agents for use against lepidopterous pests in greenhouses. The solitary endoparasitoid Meteorus gyrator (Thunberg) attacks a range of macrolepidopterous larvae, including those of some important horticultural pest species. Laboratory trials designed to investigate the biology of M. gyrator on larvae of the tomato moth, Lacanobia oleracea Linnaeus, reveal that this parasitoid is capable of parasitizing all larval stages of its host, third instars being parasitized most frequently. Each female parasitoid lives for up to 40 days (at 25 degrees C), ovipositing into an average of 78 hosts. Preadult development is rapid ( approximately 2 weeks), and the sex ratio of offspring is 1:1. Parasitism by M. gyrator suppresses the growth of both early and late host instars, and there is a concomitant reduction in the amount of food consumed (overall feeding reduction over a 12 day period is 68%). Our results indicate that inoculative releases of M. gyrator could provide effective biological control of L. oleracea and other noctuid pests of greenhouses.

The effect of snowdrop lectin (GNA) delivered via artificial diet and transgenic plants on Eulophus pennicornis (Hymenoptera: Eulophidae), a parasitoid of the tomato moth Lacanobia oleracea (Lepidoptera: Noctuidae).

Snowdrop lectin (Galanthus nivalis agglutinin, GNA) has previously been shown to confer significant levels of protection against the lepidopteran pest Lacanobia oleracea when expressed in transgenic potato. The effect of GNA on the parasitism of L. oleracea by the gregarious ectoparasitoid Eulophus pennicornis was investigated. Maize-based, and potato leaf-based diets containing GNA, and excised transgenic potato leaves expressing GNA, were fed to L. oleracea larvae from the beginning of either the third or fourth larval instar. Lacanobia oleracea larvae were individually exposed to single mated adult female E. pennicornis parasitoids from the fifth instar onwards.The success of the wasp was not reduced by the presence of GNA in any of the diets, or by the length of feeding of the host prior to parasitism. However, the mean number of wasps that developed on L. oleracea reared from the third instar on the GNA-containing maize diet was significantly higher than on the controls (20.6 and 9.3 adults/host respectively). In all other cases differences were not significant. Eulophus pennicornis progeny that developed on L. oleracea reared on GNA-containing diets showed little or no alteration in size, longevity, egg load and fecundity when compared with wasps that had developed on hosts fed the respective control diets.The results suggest that expression of GNA in transgenic crops to confer resistance to lepidopteran pests will not adversely affect the ability of the ectoparasitoid E. pennicornis to utilise the pest species as a host.