Host suitability of UV‐irradiated eggs of three Lepidoptera species for rearing Trichogrammatoidea lutea Girault (Hymenoptera: Trichogrammatidae)

Abstract

To develop a rearing programme for the egg parasitoid Trichogrammatoidea lutea for augmentative biological control, the effects of ultraviolet (UV) irradiated host eggs were evaluated on the number of eggs parasitized, development time, number of progeny and sex ratio of T. lutea, using eggs of the lepidopteran species Helicoverpa armigera, Chilo partellus and Cadra cautella as hosts. UV‐irradiation of 13 min was sufficient to kill embryos of all three hosts. The highest mean percentage parasitism on UV‐irradiated and un‐irradiated eggs occurred on those of H. armigera (47.8% and 33.3%) and C. cautella (33.2% and 55.5%), followed by C. partellus (6.6% for both). The mean number of individuals emerged per single parasitized host of UV‐irradiated and un‐irradiated eggs was highest for H. armigera (2.5 and 2.1) and lower for C. partellus (1.3 and 1.4) and C. cautella (0.9 and 0.8). The sex ratio of T. lutea was female‐biased on UV‐irradiated eggs of H. armigera, on UV‐irradiated and un‐irradiated eggs of C. cautella, and male‐biased for C. partellus eggs and un‐irradiated eggs of H. armigera. The developmental time of T. lutea from egg to adult male and female differed slightly between UV‐irradiated and un‐irradiated eggs. Overall, UV‐irradiation of host eggs had negligible effects on percent parasitism, number of progeny per parasitized egg and sex ratio of T. lutea. Of the three lepidopteran species evaluated, H. armigera appears to be the most suitable host for mass‐rearing of T. lutea. The results indicate that UV‐irradiation of Lepidoptera eggs is suitable for mass rearing of T. lutea.

Effect of fertilized, unfertilized, and UV‐irradiated hosts on parasitism and suitability for Trichogramma parasitoids

“…Our no-choice tests demonstrated that the three Trichogramma parasitoids, especially T. japonicum and T. leucaniae, had comparable parasitism on fertilized and UVF-treated C. cephalonica eggs, which was similar to previous findings on L. botrana, H. armigera, and E. kuehniella hosts (Moreno et al, 2009;Mawela et al, 2010;St-Onge et al, 2014). However, our choice test was the first to show that Trichogramma parasitoids preferred UVF hosts over fertilized or unfertilized hosts.…”

“…All Trichogramma parasitoids developed slowest on unfertilized hosts. Trichogramma japonicum or T. leucaniae had similar developmental times on fertilized and UVF-treated C. cephalonica eggs, which was like the results of T. cacoeciae on freshly laid L. botrana eggs, and of T. lutea on eggs of H. armigera, C. partellus, and C. cautella (Moreno et al, 2009;Mawela et al, 2010). A previous study showed that gamma-irradiated hosts did not affect developmental time of T. evanescens and Trichogrammatoidea bacterae Nagaraja (El-Mandarawy & Rizk, 2002).…”

“…Trichogramma japonicum or T. leucaniae had similar developmental times on fertilized and UVF-treated C. cephalonica eggs, which was like the results of T. cacoeciae on freshly laid L. botrana eggs, and of T. lutea on eggs of H. armigera, C. partellus, and C. cautella (Moreno et al, 2009;Mawela et al, 2010). Overall, T. leucaniae had the longest developmental time, followed by T. japonicum and T. chilonis.…”

Ecological responses to UV radiation: interactions between the biological effects of UV on plants and on associated organisms

“…By contrast, the more ecological literature on host‐mediated effects on herbivory deals with UV‐B and largely with chewing insects, especially caterpillars (Ballaré et al 1996, 2011, Rousseaux et al 2004, Caputo et al 2006, Foggo et al 2007). While there are points of overlap between these research areas, for example the role of UV‐B in thrip vision and behavior (Mawela et al 2010) or of host quality on aphids (Kuhlmann and Müller 2009, 2010b), the general lack of integration in research into UV effects on crop–herbivore interactions is a significant constraint in obtaining a solid overview of how a particular UV environment might contribute to the totality of plant–herbivore interactions. Of course, these effects of plant–herbivores interactions need also to be considered in the context of the wider effects of UV manipulation, not least if UV responses are to be effectively exploited in horticulture.…”

Toxicity of Bacillus thuringiensis Cry proteins to Helicoverpa armigera (Lepidoptera: Noctuidae) in South Africa

“…armigera eggs were obtained from a culture maintained at the Agricultural Research Council (Pretoria, South Africa). This culture was established with specimens collected from the Springbok Flats (29°40 0 S 17°53 0 E) in 1974 and supplemented in 2006 with specimens collected from cotton plants near Groblersdal (25°15 0 S 29°25 0 E) in Mpumalanga, South Africa (Mawela et al, 2010). Larvae were reared in our laboratory on a wheat-germ based artificial diet (Bot, 1966).…”