Side effects of grain protectants on biological control agents: How Hyptis plant extracts affect parasitism and larval development of Dinarmus basalis

Abstract

Dinarmus basalis Rondani (Hymenoptera: Pteromalidae), an ectoparasitoid of bruchid pests of stored cowpeas (Vigna unguiculata), is a potential biological control agent. We investigated whether grain protectants from Hyptis spicigera and H. suaveolens (Lamiaceae) disturb parasitism and postembryonic growth of the parasitoid. When cowpeas containing bruchid larvae were treated before being placed in the presence of D. basalis females, the rate of parasitism decreased on average up to 24% and 47% in the presence of, respectively, leaf dry powder and essential oils from both plant species. The estimated larval mortality was higher on treated (9.55 to 28.6%) than on non-treated parasitized hosts (2.8%), depending on the plant species and the plant extract tested. Additional larval mortality was higher for essential oil, and for H. suaveolens. An in-depth analysis of the pre-imaginal development in capsules adapted for this purpose showed that without treatment, mortality was recorded only for eggs and the first two larval stages. With treatment, mortality not only significantly increased on eggs but also spanned all other pre-imaginal stages. Pre-imaginal development was also significantly extended in the presence of treatment, depending on the type of extract and dose used. In conclusion, both plant species exert acute toxicity on D. basalis larvae and also act as growth inhibitors. These results provide additional information that enable us to move towards the harmonious use of allelochemical compounds from plants while protecting biocontrol agents from their adverse effects.

Insecticidal Activity of Plant Powders against the Parasitoid, Pteromalus venustus, and Its Host, the Alfalfa Leafcutting Bee

“…Concerns over the safety of the Vapona ® vapor for farmers in the confined incubators, together with the risk of the residues for the developing ALBs, provided the impetus to investigate alternative control measures for this parasitoid. Previous studies suggest that several EOs are harmful to beneficial parasitoids (Braconidae [ 21 ], Platygastridae [ 33 ], Pteromalidae [ 22 , 23 , 24 , 25 , 31 , 32 , 34 ], Trichogrammatidae [ 23 , 30 , 34 , 35 ]) applied in IPM programs for stored product pests. We investigated the contact toxicity of fifteen plant powders from seven plant families against adult P. venustus , but also examined whether exposure to the plant materials was safe for adult male ALBs.…”

“…In this scenario, the released vapor can travel throughout the cocoon matrix, poisoning the parasitoid larvae or emerging adult parasitoids. In one earlier study, plant powders from the family Lamiaceae reduced the rate of parasitism or the reproductive activity of a beneficial Pteromalid wasp (24%), and reduced larval parasitoid development (28%), which is suggestive of reproductive toxicity and fumigant properties [ 31 , 32 ]. Many studies have monitored the fumigant properties of EOs against beneficial parasitoids.…”

“…We demonstrated significant adult P. venustus mortality after exposure to oregano and ginger powders, but not with thyme or basil powders. EOs from several other plant families (Apiaceae, Lauraceae, Mytraceae, Zingiberaceae, Lamiaceae) are effective fumigants for beneficial parasitoids or Coleopteran pests of stored products, such as grains [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ].…”

“…Instead, as part of developing an integrated pest management (IPM) program for controlling stored product pests of grains, the impact of plant powders on one of the biocontrol agents, beneficial parasitoids or wasps, was evaluated. A diverse group of plant powders or their EOs from eight families (Apiaceae [ 30 ], Euphorbiaceae [ 25 ], Lamiaceae [ 22 , 31 , 32 , 33 , 34 ], Leguminosae [ 35 ], Myrtaceae [ 21 ], Poaceae [ 22 , 24 ], Solanaceae [ 35 ] and Zingiberaceae [ 23 , 34 ]), adversely affected beneficial parasitoids by increasing adult mortality, reducing the rate of parasitism, repelling the parasitoid, reducing adult longevity and reducing the emergence of the developing parasitoids. This suggests that plant powders may also be efficacious for P. venustus .…”

Repellency and Bioactivity of Caatinga Biome Plant Powders againstCallosobruchus maculatus(Coleoptera: Chrysomelidae: Bruchinae)

“…However, products from this plant species can cause detrimental effects on natural enemies in storage environments (Sanon et al 2011), thus requiring caution when used as grain protectants. In addition, other plant species of the Cleome genus showed repellent actions against ticks (Parasitiformes) and insects (Ndungu et al 1995;Nyalala & Grout 2007), but the present study is the first to report on the insecticidal/repellent potential against C. spinosa.…”