2 Nigeria, Canthium mannii in Cameroon, Melia azedarach in Brazil, and Cucurbita moschata in Guadeloupe, respectively. In Cameroon, Ageratum conyzoides commonly called “king of herbs” is used to treat diﬀerent human ailments and as worm medicine in some countries. In the present study, a comparative assay was performed to evaluate the ovicidal and larvicidal properties of aqueous and ethanolic extracts of the leaves of Ageratum conyzoides against Heligmosomoides bakeri, a gastrointestinal nematode parasite of rodents. 2. Materials and Methods The A. conyzoides leaves used in this study were harvested in Dschang, Menoua division, West Region of Cameroon. They were then dried in an oven at 50◦C for 7 days, ground, and stored in airtight plastic bags in the laboratory for further use. 2.1. Preparation of Extracts. Two types of extracts (aqueous and ethanolic) were prepared to compare their activities. Ethanolic Extract. The procedure used is as described by Wabo Pone´ et al. [5, 6]. Brieﬂy, 445 grams of stored powder were macerated in 4 liters of ethanolic 95%. The mixture was stirred daily and 72 hours later ﬁltered through a ﬁlter paper of pore size 2.5 µm. The ethanolic extract was obtained using the procedure described by Ciulei [10]. This was followed by the dilution of 100 mg of the extract (concentrated using a rotary evaporator) with 1 ml of 5% tween which helped dilute the extract and to facilitate the mixing with water. After 5–10 min, distilled water was added to obtain a total volume of 10 mL which produced a stock solution of 10 mg·mL−1 from which a series of dilutions were made to obtain solutions of 1.250, 2.5, 5.0, and 7.5 mg·mL−1 concentrations. The ﬁnal tested concentrations were 0.625, 1. 25, 2.5, and 3.75 mg·mL−1 Aqueous Extract. The above procedure was used for the aqueous extract except that distilled water was used and the maceration took 48 hours (to avoid fungal growth). Also, the solvent was dried for 24 hours in an oven heated to 50◦C. 2.2. Reference Drug. The reference drug, Mebendazole (MBZ), was used only for the larvicidal tests. The drug was bought in a local pharmacy and diluted with distilled water (DW) to obtain a stock solution with the same concentration as with organic extracts. The negative controls used for the bioassay were 5% tween and DW. 2.3. Recovery of Nematode Eggs. Heligmosomoides bakeri (previously known as Nematospiroides dubius and H. poly- gyrus; see [11, 12]) fresh eggs were obtained from the faeces of experimentally infected mice according to Michael et al. [13]. Brieﬂy, 3 g of faeces were collected, homogenised in a mortar, suspended in saturated salt solution (0.4% NaCl), and cleaned of organic debris by ﬁltration through sieves (1 mm and 150 µm) into a 100 mL beaker. The contents of the later were poured into four tubes and centrifuged Veterinary Medicine International at 1000 g for 5 min. The supernatant containing eggs was poured through a 45 µm mesh sieve. The material retained on the sieve and containing eggs was washed with tap water to remove the salt solution. The sieve was then turned over, the opposite side was washed with tap water and eggs were thus collected in a Petri dish (Ø = 16 cm) [14]. 2.4. Evaluation of Ovicidal Activity. The ovicidal eﬃcacy test of the diﬀerent extracts was performed using two diﬀerent procedures. To assess the eﬀects of the extracts on fresh eggs, 1mL of suspension containing 30 parasite eggs was distributed in each of 12 Petri dishes (35 mm Ø × 10 mm) and mixed with the same volume of a speciﬁc concentration of a given extract. The Petri dishes were covered and the eggs incubated at room temperature for 24 hours, after which 2 to 3 drops of Lugol’s iodine were added in each Petri dish to ﬁx the diﬀerent life cycle stages and the number of embryonated eggs per Petri dish was counted under a microscope (at 4x magniﬁcation). The percentage of embryonation (EM%) was determined as follows [5]: EM(%) = Number of embryonated eggs Number of eggs in culture × 100. (1) To assess the eﬀects of the extracts on the hatching mecha- nism, the same number of unembryonated eggs, distributed in Petri dishes as above, was allowed at room temperature for about 24 hours until the eggs had developed to the fully embryonated prehatch stage. When the ﬁrst stage larvae became transparent and were actively moving within the egg envelope (>90% in the control Petri dish), 1 ml of a range of each concentration of extract was added to Petri dishes. The Petri dishes were then covered and incubated for a further 6 hours at room temperature (24◦C) to allow hatching to be completed in the control dish. Thereafter, 2 to 3 drops of Lugol’s iodine were added to each Petri dish to ﬁx the diﬀerent life cycle stages and all embryonated eggs. The ﬁrst- stage larvae (L1) were counted under a microscope (at 4x magniﬁcation). The hatching rate (HR%) was computed as follows [6]: Number of L1 larvae HR(%) = Number of embryonated eggs in culture (2) × 100. 2.5. Recovery of Nematode Larvae. Eggs were cultured using the technique described by Smyth [15]. Brieﬂy, 3 ml of the egg suspension was poured on ﬁlter paper at the bottoms of two Petri dishes, which were then covered to maintain a high relative humidity (65–67%) to prevent the dishes from drying out, and was stored at 24◦C. After 3 and 4-5 days of incubation, L1 and L2 larvae, respectively, were observable in Petri dishes and were concentrated with a Baermann apparatus [15, 16]. 2.6. Evaluation of Larvicidal Activity. To assess the eﬀects of the extracts on L1 and L2 larvae, 1 mL of a solution containing about 30–40 parasite larvae was distributed in