Lack of intraspecific biological variation between two geographical populations of Oomyzus sokolowskii (Hymenoptera: Eulophidae), a gregarious larval–pupal parasitioid of Plutella xylostella (Lepidoptera: Plutellidae)

The chalcid, Oomyzus sokolowskii Kurdjumov has been recorded in many parts of the world as a major larval-pupal, gregarious endoparasitoid of the diamondback moth, Plutella xylostella (Linnaeus), a serious pest of brassica vegetable crops worldwide. This study investigated intraspecific variation between two populations of O. sokiolowskii, one from Cape Verde Islands, West Africa and the other from Hangzhou, China. In all crosses and backcrosses between the two geographical populations, the numbers of progeny and sex ratio of progeny were similar to those obtained within each of the populations, demonstrating complete reproductive compatibility between the two populations. The two populations showed similar responses to temperature with respect to development time and survival of immature stages. Observations on the interactions between the two O. sokolowskii populations and Cotesia plutellae (Kurdjumov), another major parasitoid of P. xylostella, showed that neither population could achieve successful parasitism of P. xylostella larvae already parasitized by C. plutellac. However, both O. sokolowskii populations could achieve hyperparasitism by ovipositing into a mid-late stage larva of C. plutellae developing inside the primary host. Contrary to earlier reports, no evidence of intraspecific variations in ability to hyperparasitize between these two populations of O. sokolowskii was found.

Sugarcane moth borers (Lepidoptera: Noctuidae and Pyraloidea): phylogenetics constructed using COII and 16S mitochondrial partial gene sequences

Sugarcane moth borers are a diverse group of species occurring in several genera, but predominately within the Noctuidae and Pyraloidea. They cause economic loss in sugarcane and other crops through damage to stems and stalks by larval boring. Partial sequence data from two mitochondrial genes, COII and 16S, were used to construct a molecular phylogeny based on 26 species from ten genera and six tribes. The Noctuidae were found to be monophyletic, providing molecular support for the taxonomy within this subfamily. However, the Pyraloidea are paraphyletic, with the noctuids splitting Galleriinae and Schoenobiinae from the Crambinae. This supports the separation of the Pyralidae and Crambinae, but does not support the concept of the incorporation of the Schoenobiinae in the Crambidae. Of the three crambine genera examined, Diatraea was monophyletic, Chilo paraphyletic, and Eoreuma was basal to the other two genera. Within the Noctuidae, Sesamia and Bathytricha were monophyletic, with Busseola basal to Bathytricha. Many species in this study (both noctuids and pyraloids) had different biotypes within collection localities and across their distribution; however the individual biotypes were not phylogenetically informative. These data highlight the need for taxonomic revisions at all taxon levels and provide a basis for the development of DNA-based diagnostics for rapidly identifying many species at any developmental stage. This ability is vital, as the species are an incursion threat to Australia and have the potential to cause significant losses to the sugar industry.

Foraging behaviour of Helicoverpa armigera first instar larvae on crop plants of different developmental stages

Understanding how insect pests forage on their food plants can help optimize management strategies. Helicoverpa armigera (Hubner) (Lep., Noctuidae) is a major polyphagous pest of agricultural crops worldwide. The immature stages feed and forage on crops at all stages of plant development, damaging fruiting and non-fruiting structures, yet very little is known about the influence of host type or stage on the location and behaviour of larvae. Through semi-continuous observation, we evaluated the foraging (movement and feeding) behaviours of H. armigera first instar larvae as well as the proportion of time spent at key locations on mungbean [Vigna radiata (L.) Wilczek] and pigeon pea [Cajanus cajan (L.) Millspaugh] of differing developmental stages: seedling- and mature (flowering/pod fill)-stage plants. Both host type and age affected the behaviour of larvae. Larvae spent more time in the upper parts of mature plants than on seedlings and tended to stay at the top of mature plants if they moved there. This difference was greater in pigeon pea than in mungbean. The proportion of time allocated to feeding on different parts of a plant differed with host and age. More feeding occurred in the top of mature pigeon pea plants but did not differ between mature and seedling mungbean plants. The duration of key behaviours did not differ between plant ages in either crop type and was similar between hosts although resting bouts were substantially longer on mungbeans. Thus a polyphagous species such as H. armigera does not forage in equivalent ways on different hosts in the first instar stage.