R. K. Stewart

Body size as an indicator of parasitoid quality in male and female Anagyrus kamali (Hymenoptera: Encyrtidae)

The parasitoid Anagyrus kamali Moursi was recently introduced into the Caribbean as a biological control agent against the hibiscus mealybug, Maconellicoccus hirsutus Green. In the laboratory, parasitoid size, as measured by left hind tibia length, was positively correlated with several indicators of the parasitoids fitness: longevity, mating preference, fecundity, reproductive longevity, progeny emergence and sex-ratio. When fed ad libidum with honey drops, large male parasitoids lived significantly longer (29.1 +/- 6.5 days) than small ones (18.4 +/- 5.7 days). Large females also lived significantly longer (35.4 +/- 10 days) than small females (27.9 +/- 9.6 days). Females showed no significant mating preference between large and small males. Lifetime fecundity was positively correlated with the size of adult females and ranged from 37 +/- 21 eggs for small females to 96 +/- 43 eggs for large ones. The reproductive longevity, daily oviposition rate, and number of progeny were also higher among large parasitoids. The sex ratio of progeny from small female parasitoids was higher (0.76 +/- 0.24) than that of large individuals (0.47 +/- 0.18).

Effect of host density, temperature, and photoperiod on the fitness of Anagyrus kamali, a parasitoid of the hibiscus mealybug Maconellicoccus hirsutus

The peformance of the parasitoid Anagyrus kamali Moursi [Hymenoptera: Encyrtidae], as a function of host density, temperature, and photoperiod was investigated with the objective to optimize a mass‐rearing system in the context of a biological control program. The number of hosts parasitized at densities varying from 2–100 hibiscus mealybug (HMB), Maconellicoccus hirsutus Green [Homoptera: Pseudococcidae], corresponded to a type II‐III functional response in fixed‐time conditions and a type III in variable‐time conditions. Twenty‐six percent of the oviposited eggs led to progeny emergence with a sex ratio of 0.49±0.102 (M/F), regardless of host density. Fecundity and oviposition period under six abiotic combinations (i.e., two temperatures (26±2 °C and 32±2 °C) and three photoperiods (L0:D24, L12:D12, L24:D0)) were measured. Lifetime fecundity and reproductive life were significantly affected by temperature and photoperiod conditions. Optimum female parasitoid lifetime fecundity was attained at 26±2 °C, L0:D24 with an average of 116.1±17.43 eggs. At 32±2 °C, L24:D0 and L12:D12, an average of 79.4±34.57 and 85.8±35.81 eggs were laid, respectively. Reproductive longevity was maximal at 26±2 °C, L0:D24 with 12±4.85 days of oviposition. Because the parasite A. kamali can be reared optimally without light, this may save tremendous energy costs.

Immune response of the hibiscus mealybug, Maconellicoccus hirsutus Green (Homoptera: Pseudococcidae), to oviposition of the parasitoid Anagyrus kamali Moursi (Hymenoptera: Encyrtidae).

Anagyrus kamali Moursi has been recently introduced into the Caribbean as a biological agent against the hibiscus mealybug, Maconellicoccus hirsutus Green. This host has a cellular defense reaction that involves encapsulation and melanization of the endoparasitoid egg. The impact of this immune response on the parasitoid progeny was assessed, as well as the response of the parasitoid countermeasures to overcome it. Under laboratory conditions, significant differences in the immune response were found for different developmental stages of M. hirsutus. The intensity of the immune response varied between second instar, third instar and adult mealybugs. After 30 h, the level of encapsulation was the highest for eggs oviposited in adults: 58% of eggs were encapsulated, followed by third (32%) and second (4%) instars. Three days after oviposition 23, 44 and 86% of the parasitoid eggs oviposited, respectively, in adult, third and second instars were not encapsulated. The unencapsulated parasitoid eggs could hatch and continue their development. Adult mealybugs required 30 h to encapsulate 50% of the eggs, whereas in second and third instars, 50% level encapsulation was never reached. Superparasitism had a saturating effect on the immune system; reduced levels of encapsulation occurred when more than 10 eggs were oviposited in a single mealybug. Wasp larvae were never encapsulated by M. hirsutus.

Mutual Interference Among Female Anagyrus kamali Moursi (Hymenoptera: Encyrtidae) and its Impact on Fecundity, Progeny Production and Sex Ratio

The solitary endoparasitoid Anagyrus kamali Moursi was introduced to the Caribbean to control populations of Hibiscus Mealybug (HMB) Maconellicoccus hirsutus Green. As part of a biological control programme, mass rearing of A. kamali should produce a maximum of good quality female wasps, because only female parasitoids attack the mealybug. In laboratory experiments conducted at 27 +/- 2°C, mutual interference between female parasitoids on the total oviposition, progeny production and sex ratio was assessed at five parasitoid densities: i.e. 1, 2, 5, 10 and 20 female wasps per 50 mealybugs. Oviposition rates of females decreased with increasing female density, without significantly affecting the sex ratio (average across densities of 0.49 +/- 0.322) (male/female). Under mass-rearing conditions, an increase of the female density from 25 to 75 individuals per cage resulted in an increase of the progeny production from 266 +/- 70.1 to 877.5 +/- 393.3 parasitoids. From 75 to 100 females released per cages, the progeny production was not significantly different with 877.5 +/- 393.3 and 965.3 +/- 608.3 parasitoids produced, respectively. Regardless of the female density, progeny sex ratio remained stable at an average of 0.45 +/- 0.095. As a result, the best efficiency of the mass-production system was obtained at a density of 75 females per cage. However, parasitoid production at this density was inferior to singly caged females by about 50%.

Field Efficacy and Baseline Toxicities of Pyriproxifen, Acetamiprid, and Diafenthiuron Against Bemisia tabaci Gennadius (Homoptera: Aleyrodidae) in Burkina Faso (West Africa)

Bioassays were conducted in 2001 and 2002 to estimate toxicities and dose‐response relationships of 24 Bemisia tabaci Gennadius populations to pyriproxifen, acemitaprid, and diafenthiuron. LC50s ranging from 0.014 to 0.096 mgL− 1, 0.60 to 1.3 mgL− 1, and 3.5 to 6.7 mgL− 1 were observed respectively for pyriproxifen, acemitaprid, and diafenthiuron. These LC50s much lower than the field doses recommended for each compound. A fast increase in rates of mortality within a narrow range of lethal concentrations was observed for each compound, indicating that all three compounds were highly effective at killing whiteflies. In a separate experiment, pyriproxifen, acemitaprid, and diafenthiuron were tested in 2001 and 2002 to compare their effectiveness and assess their impact on parasitism in the field. In both years all three compounds significantly prevented B. tabaci populations from reaching economic injury levels in cotton and minimized adverse effects on parasitism. Our results provide for the first time baseline toxicological, field efficacy, and effect on parasitism data for pyriproxifen, acemitaprid, and diafenthiuron against B. tabaci in West Africa. These compounds should be included in a resistance management program of the cotton pest complex and their use should be restricted to prevent the building of resistance in B. tabaci populations.

Effects of neem seed kernel extracts on egg and larval survival of the sorghum shoot fly, Atherigona soccata Rondani (Dipt., Muscidae)

A two‐year study was conducted to evaluate the effects of neem extracts on egg and larval mortality of the sorghum shoot fly, Atherigona soccata Rond. Field experiments were conducted in 1990 and 1991 in a sorghum field at Matourkou (Burkina Faso, West Africa). The following treatments were applied: 1. carbofuran 5 G, 2. 20 kg/ha neem seeds/500 1 water, 3. 20 kg/ha neem seeds/500 1 water + 2.5 l/ha adhesol, 4. 30 kg/ha wild neem seeds/500 1 water + 2.5 l/ha adhesol, 5. 2.5 l/ha adhesol, 6. control (untreated plots). Significant differences among treatments were observed in the number of eggs laid, and the percentage of dead hearts. Significantly fewer eggs and dead hearts were observed in plots treated with neem extracts compared with adhesol and control. In the laboratory, the treatments were: 1. commercial neem oil containing 0.63% azadirachtin, 2. local neem oil, 3. 40 g seed kernels/l/water, 4. 40 g seed kernels/l water + 5 ml adhesol, 5. 60 g seed kernels/l water + 5 ml adhesol, 6. 5 ml adhesol/l water, 7. control (untreated eggs). All neem seed extracts gave a significant lower percentage of egg hatching than the adhesol and control treatments. In larval survival experiments, commercial and local neem oil were not used. All treatments showed a significantly higher larval mortality compared with the controls.

Parasitism activity of Peristenus spp. (Hymenoptera: Braconidae) on Lygus lineolaris (Hemiptera: Miridae) nymphs prior to the establishment of P. digoneutis in southwestern Quebec

Abstract Parasitism of tarnished plant bug nymphs, Lygus lineolaris (Palisot de Beauvois) was investigated on different weeds and on lettuce, celery and alfalfa-clover, in a muck soil area of southwestern Quebec. The phenology of parasitism, defined as the time during which female parasitoids are active in the field, was evaluated. Two nymphal parasitoid species were found: Peristenus pallipes (Curtis) and P. pseudopallipes (Loan). Lygus lineolaris was most abundant on stinging-nettle with levels of parasitism of 17% (P. pallipes) and 27% (P. pseudopallipes) and on alfalfa-clover with levels of parasitism of 25% (P. pallipes) and 8% (P. pseudopallipes). On lettuce, parasitism by P. pseudopallipes was below 4% while no parasitism was observed on celery. The dissection and rearing methods were used to estimate parasitism, and dissection usually yielded parasitism levels higher than rearing. Degree-days requirements of both host and parasitoids were used to calculate the period of activity of parasitoid adults. The estimates of adult activity were 47 days from late May to early July for P. pallipes, and 42 days from mid-July to late August for P. pseudopallipes.

Relative abundance of Bemisia tabaci Gennadius (Homoptera: Aleyrodidae) and its parasitoids, and the impact of augmentative release of Eretmocerus spp. (Hymenoptera: Aphelinidae) on the population dynamics of the pest in Burkina Faso (West Africa)

Whitefly infestations and parasitism were monitored year-round in overlapping cotton crops sown on three dates in Burkina Faso. The relative abundance of B. tabaci (Gennadius) and its parasitoids, Eretmocerus spp. and Encarsia spp., was recorded in control and insecticide-sprayed plots. Low B. tabaci populations developed during the first half of the rainy season. Pest populations increased when rainfall was ending, and the levels reached were higher in insecticide-treated plots (48 nymphs/leaf) than in control plots (25 nymphs/leaf). Parasitism reached 88.7% in control plots, and 53.7% in insecticide-treated plots. Eretmocerus spp. nymphs were more abundant than Encarsia spp. in both treated and control plots. A positive and significant curvilinear relationship was observed where % parasitism, on a linear scale, rose to a plateau with logarithmic increase in host density. In general % parasitism was correlated with the abundance of pest populations except in March and April where parasitism increased while B. tabaci populations decreased. In a separate experiment, adult Eretmocerus spp. were released into caged cotton plants to study the impact of augmentative releases of the parasites on the population dynamics of the pest. Pest densities increased from 1.47 nymphs/leaf to 39.4 nymphs/leaf in the control, but were reduced to 0.8 and 0.6 nymphs/leaf in the cages where, respectively, 4 and 8 parasitoids were released per plant. It appears that parasitism is an important factor reducing B. tabaci populations during and after the cotton-growing season, and that Eretmocerus spp. are promising biological control candidates against the pest in cotton.

Effects of intercropping sorghum-cowpea on natural enemies of the sorghum shoot fly, Atherigona soccata (Diptera: Muscidae), in Burkina Faso.

Experiments were conducted in 1990 and 1991 at Matourkou near Bobo-Dioulasso, Burkina Faso (West Africa), to study the effect of intercropping sorghum-cowpea, Sorghum bicolor L. (Moench)—Vigna unguiculata (Walp.), on the natural enemies of the sorghum shoot fly, Atherigona soccata Rondani (Diptera: Muscidae). Sampling was done weekly, on six occasions starting 10 days after sowing. Natural enemies of eggs were Trichogrammatoidea simmondsi Nagaraja (Hymenoptera: Trichogrammatoidae), Tapinoma sp. (Hymenoptera: Formicidae), Fusarium sp. and a bacterium, Corynebacterium sp. Other insect species included a thysanopteran (Phlaeothripidae, Haplothripinae) and Dicrodiphosis sp. (Diptera: Cecidomyiidae) which were also associated with the sorghum shoot fly eggs. No significant differences were observed between the pure sorghum and the intercropped sorghum-cowpea with respect to T. simmondsi parasitism. Larval parasitoids were Neotrichoporoides nyemitawus Rohwer (Hymenoptera: Eulophidae), (6 to 17.50% of parasitism...

Effect of precipitation on emergence of Smicronyx guineanus Voss and Sm. umbrinus Hustache (Coleoptera: Curculionidae) adults and soil vertical distribution of pupae

Abstract A three‐year study was conducted to evaluate the effect of rainfall on the emergence of Smicronyx guineanus Voss and Sm. umbrinus Hustache adults and the vertical distribution of pupae in the soil. Field collection of data was conducted in 1990, 1991 and 1993 in sorghum and millet fields infested by Striga hermonthica at Kaya and Ouahigouya (Burkina Faso, West Africa). In 1993, experiments were conducted in an insectary with the use of simulated rainfall. Ten, 20, 30, 40, and 50 mm of rainfall were stimulated and the effect on the pupal emergence noted. Each of the six levels of the factor ‘rainfall’ was tested with pieces of Striga flower, stem and no Striga present. A highly significant difference was observed among rainfall heights and an optimum rainlall of 30–40 mm was found for Smicronyx adult emergence. No interaction was found between rainfall and Striga. To assess the vertical distribution of Smicronyx pupae in soil, five field quadrats were collected at Kaya and Ouahigouya respectively ...