Holger Philipsen

Recycling of entomopathogenic nematodes in Delia radicum and in other insects from cruciferous crops

Larvae of Deliaradicum Linnaeus (Diptera: Anthomyiidae) wereexposed to Steinernema feltiae Filipjev(Rhabditida) to study the ability of thenematodes to fulfill their life cycle (recycle)in this host. In addition, the recycling ofSteinernema and Heterorhabditis(Rhabditida) species was studied in larvae ofthe following insects: Meligethes spp.Stephens (Coleoptera: Nitidulidae),Dasyneura brassicae Winnertz (Diptera:Cecidomyidae), Ceutorrhynchus assimilisPaykull, C. pallidactylus Marsham (Coleoptera: Curculionidae) and Mamestrabrassicae Linnaeus (Lepidoptera: Noctuidae).All larval instars of D. radicum werestudied (larvae live and pupate in soil)whereas the final instars of the remaininginsects were studied (larvae only pupate in soil).On average, the following numbers of infectivejuveniles were produced in the different hosts:1,200–1,400 in C. assimilis; 700–1,300 inMeligethes spp. and 47,000 in M.brassicae. In D. radicum, around 400infective juveniles were produced on average inthe smallest larvae and around 3,500 in thelargest larvae. The highest number of nematodesrecorded in a D. radicum larva (thirdinstar) was 9,500 infective juveniles. Thenumber of nematodes produced in D.radicum cadavers was positively related to thesize of the insect host, but large variationwas observed.

Susceptibility of Meligethes spp. and Dasyneura brassicae to entomopathogenic nematodes during pupation in soil

The susceptibility of pupating larvae of pollen beetles, Meligethes spp. Stephens (Coleoptera: Nitidulidae) and brassica pod midges, Dasyneura brassicae Winnertz (Diptera: Cecidomyidae) to entomopathogenic nematodes (Nematoda: Rhabditida) was studied in the laboratory. The results showed that brassica pod midge larvae were almost unaffected by the tested nematodes (Steinernema bicornutum, S. feltiae and Heterorhabditis bacteriophora) whereas successful pupation of pollen beetle larvae was reduced with increasing number of nematodes (S. bicornutum, S. carpocapsae, S. feltiae and H. bacteriophora). The exposed larvae had been collected in the field and some of the pollen beetle larvae were parasitised by parasitoid wasps. It appeared that parasitised larvae were less affected by nematodes than non-parasitised larvae.

Seasonal population dynamics of inoculated and indigenous steinernematid nematodes in an organic cropping system

This study was based on naturally occurring and inoculated populations of steinernematid nematodes. The nematode populations were monitored spring and autumn in two following years in an organic cropping system and changes in population size were related to the presence of potential insect hosts. Nematode population were estimated in terms of nematode incidence (percentage of positive soil samples) by using Tenebrio molitor larvae as bait. The population of naturally occurring nematodes (Steinernema affine (Bovien) and S. feltiae (Filipjev)) was generally at a low level (0-17 % incidence for S. affine and 0-18 % incidence for S. feltiae). Inoculated S. feltiae established well in half of the plots where inoculation had been performed and reached incidences of 87 %. Establishment of inoculated nematodes, and population dynamics in general, was clearly influenced by the presence of insect hosts. In crops with high densities of potential hosts (Sitona lineatus in pea and partly Delia radicum in cabbage), nematode incidence increased from spring to autumn whereas nematode incidence remained unchanged or decreased when few hosts were present (in barley, carrots, alfalfa and leek).

Occurrence of Steinernema species in cabbage fields and the effect of inoculated S. feltiae on Delia radicum and its parasitoids

Abstract  1 Seven organically grown cabbage fields were surveyed for entomopathogenic nematodes in the autumn by baiting. Nematodes were obtained from three fields with bait larvae infection ranging from 1.3–4.0%.

Estimating the incidence of entomopathogenic nematodes in soil by the use of bait insects

Soil samples were stored and baited in different ways in order to develop a bait method that could estimate the level of steinernematid nematodes in soil in a time efficient way. The method was based on incidence (proportion of samples with a given species of Steinernema). Tenebrio molitor (Coleoptera) larvae were used as bait and it was concluded that: 1) Repeated baiting in a later period improved the bait result; 2) Extension of the bait periods from one to two weeks was not necessary; 3) The precision of the estimated incidence did not improve noteworthy by taking more than 60-80 samples; 4) The minimum time required to analyse one soil sample was 6 minutes.

Education in biological control at the university level at KVL

1. Competence Why should we be concerned about education in biological control? It can be argued that most people working with this subject (scientists, extension officers etc.) do not need a particular education, but need solely a strong background in one discipline relevant for their particular approach. For example, scientists can have a background in applied entomology, plant pathology, microbial fermentation or legislation. At many universities worldwide biological control is one among other elements to be taught at courses in applied entomology, plant pathology or weed control. Students are provided with an overview, for example by having a lecture or two on the subject. Such overview lectures are mostly closely related to the application of biological control and can be excellent introductions to the subject. Such introductory lectures will potentially stimulate students to learn much more in depth and thus to obtain real qualifications in biological control. We believe that education at the university level in biological control has not yet reached its potential, but should be devoted much more attention as a subject in its own right. Students should get a chance not only to get a brief overview, but they should be able to understand fully the concept and practical possibilities. Also, we believe that the strict separation between biological control of pest insects, plant diseases and weeds is a hindrance for future scientists and other people involved in the protection of plants and husbandry, to develop a broad perspective on biological control. Therefore, we suggest that education in biological control should be based on a strong, broad view, and that this education should include as much as possible biological control of both pest insects (and other invertebrates), plant diseases and weeds. Education in biological control must be closely linked to the needs of the end-users, but should also include significant aspects of fundamental interest. At the Royal Veterinary and Agricultural University (KVL) in Denmark, overview lectures on biological control have been given for many years. Since 1988 our student have had the opportunity to choose courses devoted solely to biological control and thus to obtain defined competences in biological control. The first course was a laboratory course in biological control of insects, later a laboratory course in biological control of plant diseases and a theoretical lecture course in biological control of insect pests, plant diseases and weeds were added. The following describes the most important experience we have obtained over these years by having laboratory and lecture courses.