Bishwo P. Mainali

Behavioral Response of Western Flower Thrips to Visual and Olfactory Cues

Behavioral responses of Frankliniella occidentalis Pergande (Thysanoptera: Thripidae) to visual and olfactory cues were assessed in a cylindrical black box and a Y-tube olfactometer. Frankliniella occidentalis preferred circular shapes to other five geometrical patterns (rectangle, triangle, inverted triangle, diamond, and modified circle imitating flower petals) in multiple choice tests. In pair wise choice tests, the thrips preferred the yellow artificial flower shape to the geometrical patterns tested. Frankliniella occidentalis stayed on the artificial flower about four times longer than on the geometrical patterns. Higher numbers of thrips responded to a combination of p-anisaldehyde and artificial flower compared to the arm with only the olfactory or the visual cue. These results suggest that shape is an important cue for F. occidentalis.

Changes in Nutritional Composition of Soybean Seed Caused by Feeding of Pentatomid (Hemiptera: Pentatomidae) and Alydid Bugs (Hemiptera: Alydidae)

ABSTRACT Changes in protein, lipid, and carbohydrate content, and the weight loss of soybean seeds caused by the feeding of 6- to 7-d-old unmated male adults of the pentatomids Peizodorous hybneri (Gmelin) and Halymorpha halys (Stål), and an alydid, Riptortus pedestris (F.), were examined in the laboratory. Our goals were to determine which species had the greatest capacity to damage soybean seed and to measure the effect of that damage on the nutritional composition of soybean seed. Individuals of the three species were provided with a preweighed dry soybean seed and allowed to feed for 0, 4, 8, 12, 16, 20, and 24 d, after which the remaining seed was analyzed for any change in weight, protein, lipid, and carbohydrate concentration. Lipids, carbohydrates, and seed weights were reduced by bug feeding, and the reduction was directly proportional to feeding duration. H. halys was found to be the most voracious feeder, reducing soybean seed weight by 42% after 24 d of feeding. There was a significant interaction between species and feeding duration for changes in nutritional components. Seeds fed on by H. halys had the highest incremental increase in protein content (13%) after 24 d of feeding, followed by those fed on by R. pedestris and P. hybneri. However, carbohydrates and lipid content of the soybean seeds fed by the tested insect species were found to decrease significantly. Soybean pods at mature stages remain in the field for a long period, and findings of our study suggest that longer exposure of the mature soybean pods to these pest species in the field may lead to low-quality seeds and lower yields, and may even affect the germination potential of the seeds.

Effect of Aggregation Pheromone Trap of Riptortus pedestris (Hemiptera: Alydidae) on the Distribution and Composition of Its Egg Parasitoids

ABSTRACT The aggregation pheromone of Riptortus pedestris (F.) (Hemiptera: Alydidae) is known to attract its egg parasitoids Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) and Gryon japonicum (Ashmead) (Hymenoptera: Scelionidae). Distribution and composition of these egg parasitoids were compared in a soybean field in the presence and absence of aggregation pheromone-baited traps for two consecutive years. Three traps were installed on the edge of a soybean field, first without and then with aggregation pheromone in a before-after design, and changes in parasitism were assessed on nonviable host eggs released at distances of 9,18, 27, and 36 m from the trap. A significant interactive effect of pheromone installation and distance was found in egg parasitism by both parasitoids. Parasitism on eggs recovered from 9 m away was up to 2.2 and 3.2 times higher in presence of pheromone than without pheromone for O. nezarae and G. japonicum, respectively. Parasitism by O. nezarae was always higher than that by G. japonicum, but their relative abundance, clutch size, and sex ratio were not affected by pheromone installation, irrespective of distance from the trap. In conclusion, aggregation pheromone increases abundance of parasitoids up to 18 m from trap installation points and does not affect the relative abundance of parasitoid species.

Evaluation of yeasts in gel larval diet for Queensland fruit fly, Bactrocera tryoni

Queensland fruit fly, Bactrocera tryoni (“Q‐fly”), is Australia’s most economically important insect pest of horticultural and commercial crops especially in the eastern regions. The sterile insect technique (SIT) has been adopted as an environmentally benign and sustainable approach for management of Q‐fly outbreaks. High‐performance larval diets are required to produce the millions of flies needed each week for SIT. Yeast products contribute amino acids (protein) to fruit fly larval diets, as well as carbohydrate, fat and micronutrients, but there can be substantial variation in the nutritional composition and suitability of yeast products for use in larval diets. Gel larval diets have recently been developed for large‐scale rearing of Q‐fly for SIT, and composition of these diets requires optimization for both performance and cost, including choice of yeast products. We assessed performance of Q‐flies reared on gel larval diets that contained debittered brewer’s yeast (Lallemand LBI2240), hydrolysed yeast (Lallemand FNILS65), inactivated brewer’s yeast (Lallemand LBI2250) and inactivated torula yeast (Lallemand 2160‐50), including blends. Q‐flies performed poorly when reared on diets containing only or mostly hydrolysed yeast in terms of pupal number, pupal weight and percentage of fliers. Performance was also poor on diets containing high proportions of torula yeast. Overall, debittered brewer’s yeast is recommended as the best option for Q‐fly gel larval diet, as it is cheap, readily available, and produces flies with good performance in quality control assays. Inactivated brewer’s yeast produced flies of comparable quality with only a modest increase in cost and would also serve as an effective alternative.

Interactive influence of temperature and relative humidity on egg parasitoids of Riptortus pedestris (Hemiptera: Alydidae).

ABSTRACT Previous studies reported that of the two egg parasitoids of Riptortus pedestris (F.) (Hemiptera: Alydidae) found in Korea, Gryon japonicum (Ashmead) (Hymenoptera: Scelionidae) appears in soybean fields much earlier than Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae). To explain this phenomenon, we evaluated the interactive influence of temperature and relative humidity (RH) on the biological attributes of these parasitoids, including adult parasitoid longevity and survival. Temperature had significant effects on all the biological attributes examined for both parasitoids, while RH only affected rates of parasitism and adult emergence. Interaction between temperature and species, but not RH and species was found to affect significantly on parasitism. G. japonicum showed higher relative increment in parasitism than O. nezarae at temperatures higher than 25°C. No significant differences in progeny sex ratio were detected for either species at any temperature X humidity combination. RH had no effect on the developmental time of O. nezarae but on the developmental time of G. japonicum, which was longer at low RH. Although the biological attributes of adult parasitoids of both species showed a wide range of adaptability, but it did not explain the patterns of occurrence of these species in the field. However, G. japonicum showed greater longevity than O. nezarae at all combinations of temperature and RH and this may partially explain the seasonal pattern of occurrence of adult parasitoids in the field previously observed.

Effects of Wheat Germ Oil Concentration in Gel Larval Diets on Production and Quality of Queensland Fruit Fly, Bactrocera tryoni (Diptera: Tephritidae)

Abstract Queensland fruit fly (‘Q-fly’), Bactrocera tryoni (Froggatt) (Diptera: Tephritidae), is the most destructive insect pest of horticultural crops in Australia. The sterile insect technique (SIT) has attracted significant interest for sustainable management of Q-fly through the mass rearing and release of sterile flies. Cost-effective diets are required to rear Q-flies for SIT. Wheat germ oil (WGO) is the main source of fatty acids and vitamins in gel larval diets that are used to rear Q-fly but is an expensive ingredient. With the aim of reducing WGO cost in gel larval diet, we assessed performance of Q-flies reared on diets that varied in WGO content. Q-fly larvae were reared on two diets that differed mainly in yeast composition (‘gel diet 2006′ and ‘gel diet 2009′) and contained 0, 0.03, 0.07, 0.11, 0.15, or 1% WGO to identify reduced concentrations of WGO (and hence cost) without compromising productivity or quality. Diets containing WGO outperformed diets without WGO in development rate, pupal number, adult emergence, percentage of fliers, rate of fliers, and fecundity. Concentrations of 0.11% and above provided full benefit in gel diet 2006 (original formulation 0.15%), and concentrations of 0.15% (original formulation 1.0%) and above provided full benefit in gel diet 2009, and for both diets, a concentration-dependent decline in fly performance resulted from lower doses. Savings can be made in gel diets for mass rearing of Q-fly without compromising productivity by reducing WGO concentration.