Change in carbon stable isotope ratios of the predatory bug Orius majusculus after dietary shifts

Orius majusculus Reuter (Hemiptera: Anthocoridae) is an important component of the pest predatory complex in arable crops in Mediterranean areas. It moves between crops searching for prey, and improving knowledge on its dispersal abilities will help to develop conservation biological control strategies. Stable isotope ratios may be used as a tool for tracking insect movements, as the isotopic composition of insect tissues changes to reflect that of their diet when they undergo dietary shifts on moving between isotopically distinct crops. We carried out laboratory diet switch experiments with a stable isotope approach to infer information on dispersal of O. majusculus individuals among C3 and C4 crops to better understand isotopic field data collections. Switching the aphid food source caused a quick change in δ¹³C signatures, regardless of the original and final food source. Changes in the δ¹³C ratio of O. majusculus after diet switching fitted with an exponential model that showed similar turnover rates, and thus half‐lives, between shifting diets up to 20 days. Subsequently, whereas individuals feeding on C4 aphids did not survive, turnover rate decreased in individuals that switched from C4 to C3 aphids. However, δ¹³C traces from the original source remained in the predator until 25 days after switching, and this is enough time to help determine the movement of O. majusculus between crops in the field and to plan the timing of predator sampling and crop practices that may enhance predator ecological services. Orius majusculus that switched to a maize aphid diet showed different turnover rates between sexes, although this did not influence the pattern of switchover.     

Nutritional value of brine shrimp cysts as a factitious food for Orius laevigatus (Heteroptera: Anthocoridae)

Decapsulated cysts of the brine shrimp Artemia franciscana were assessed as a factitious food for rearing the anthocorid predator Orius laevigatus. Developmental and reproductive traits of O. laevigatus reared for a single generation on A. franciscana from three geographical locations or on gamma-irradiated eggs of the Mediterranean flour moth Ephestia kuehniella were compared. There was no effect of diet on nymphal survival but nymphal period on E. kuehniella eggs (12.2 days) was 0.7-1.6 days shorter than on the Artemia diets. The predator developed 0.5-1 day faster on cysts from San Francisco Bay (USA) than on cysts from Great Salt Lake (USA) or Macau (Brazil). Fecundity on brine shrimp cysts from different locations was similar to that on flour moth eggs (142-187 eggs/female). The biochemical composition of decapsulated cysts from San Francisco Bay was compared with that of E. kuehniella eggs. Depending on the type of analysis, Artemia cysts contained higher or similar amounts of protein as compared with E. kuehniella eggs, but amino acid patterns were generally similar. Flour moth eggs were almost three times richer in fatty acids than brine shrimp cysts, with some marked differences in fatty acid profiles. Because nutrient imbalances in a diet may be expressed only after several generations of rearing, the predator was cultured for three consecutive generations on A. franciscana cysts from San Francisco Bay. In the third generation on brine shrimp cysts, nymphs took 18% longer to develop, and adults were shorted-lived and about 60% less fecund than those maintained on E. kuehniella eggs. Brine shrimp cysts may be used as a supplement in the mass production of O. laevigatus but may not be a suitable food for long-term culturing of the predator.     

Olfactory response of the anthocorid predatory bug Orius sauteri to thrips-infested eggplants

The predator Orius sauteri (Poppius) (Heteroptera: Anthocoridae) is an effective arthropod natural enemy of thrips, especially Thrips palmi Karny (Thysanoptera: Thripidae), a serious pest of vegetables. First, we studied O. sauteri's response to the odour from thrips-infested eggplant [Solamum melongena L. (Solanaceae)] in a laboratory by two-choice experiments using a Y-tube olfactometer. When detached eggplant leaves were used as odour sources, O. sauteri preferred the volatiles from uninfested leaves to clean air. Concerning preferences among differently infested leaves, O. sauteri preferred the volatiles from plants infested with 10–100 thrips per leaf to uninfested leaves, but showed no significant preference for artificially damaged leaves over uninfested leaves. Similar results were obtained when complete plants were tested as the odour source. Second, release and recapture experiments in a greenhouse, a more realistic set of conditions, were conducted to confirm whether a significant preference for infested plants occurred at similar infestation levels as in the laboratory. Trends favouring infested plants were detected at densities of five and 500 thrips per plant; however, at the five thrips per plant, this trend was due to the large deviation seen in infested plants in only one replicate. In light of the low tolerable thrips density of eggplant, it is necessary to confirm whether artificial treatments with chemicals induce the emission of herbivore-induced plant volatiles that can attract O. sauteri and prolong its residence time on the leaf.     

The suitability of some natural and artificial substrates as oviposition sites for the insidious flower bug, Orius insidiosus

A variety of natural and artificial substrates were tested for their suitability as oviposition sites for the predatory anthocorid bug Orius insidiosus. The bugs oviposited into models of beans constructed from Parafilm, but none of the eggs laid into these models hatched. In choice tests, beans stems were preferred to both bean pods and potato sprouts. Hatching rates at 100% r.h. were highest (59%) for bean pods and significantly lower for both potato sprouts (39%) and bean stems (29%). At 60% r.h., hatching rates for bean pods (39%), bean stems (34%) and potato sprouts (33%) were similar. At 30% r.h. hatching rates for all three substrates were less than 15%. The results suggest that bean stems can be used successfully as an alternative to bean pods for the mass rearing of these biological control agents.     

Food quality of Ephestia eggs,the aphid Rhopalosiphum padi and mixed diet for Orius majusculus

We studied the food quality of the aphid Rhopalosiphum padi to the pirate bug Orius majusculus using Ephestia eggs as high-quality comparison prey. Several performance parameters were tested on individuals that had been reared and maintained on each of the two single-prey diets or on a mixed diet. All fitness parameters were lower in individuals fed aphids only, indicating poor food quality of this prey. Compared with the pure Ephestia egg diet, the mixed diet enhanced teneral mass, while adult survival and female starvation tolerance were negatively affected and all other traits were unaffected. Body protein proportions were constant across diets, whereas lipid proportion was low in the aphid treatment. Preference for aphids was lower following a monotypic aphid diet than when reared on Ephestia eggs or a mixed diet. The results confirm that R. padi is low-quality food for O. majusculus as it is for other generalist predators, even though O. majusculus may contribute significantly to population suppression of the aphid.     

Liver-based artificial diets for the production of Orius laevigatus

Different meat- and liver-based artificialdiets were designed for the generalist predatorOrius laevigatus (Fieber) (Anthocoridae)and their suitability was compared to that ofits factitious food, Ephestia kuehniellaZeller (Pyralidae) eggs. The quality of thefood was measured by its ability to promotegrowth and oviposition of the insect. Nymphaldevelopment was slower on artificial diets thanon the control food, taking 15.0–15.9 days vs.14.3 days, respectively. Survival of nymphs fedartificial diets varied from 68.0–92.5%,compared with 96% for those fed E. kuehniella eggs. Adult weights were, however,not affected by diet. Fecundity of femalesprovided with liver diets was similar to orsomewhat lower than that of females fed Ephestia eggs. Oviposition rate and egg hatchwere similar on all diets tested. The resultssuggest that beef liver was the most importantcomponent of the diets tested, offering theessential nutrients to sustain growth andreproduction of O. laevigatus.Supplementing ingredients, like ground beef,egg yolk, sucrose and vitamin C can improve thenutritional value of the diet for O.laevigatus, but effects are rather small.Artificial diets containing liver and egg yolkas the main components may prove useful to makemass production of O. laevigatus andother heteropteran predators more cost effective.     

Artemia cysts as an alternative food for the predatory bug Macrolophus pygmaeus

The suitability of cysts of the brine shrimp Artemia sp. as a factitious food for the predator Macrolophus pygmaeus Rambur was investigated. The influence of decapsulation time and hydration of the cysts on the performance of the predator were studied in the absence of plant material. A longer time of decapsulation had a positive influence on the development of the predator. Hydration of cysts had a significant impact on nymphal survival when cysts where non‐decapsulated or poorly decapsulated. An experiment in which nymphs were switched from a diet of hydrated cysts to non‐hydrated cysts showed that in the absence of plant material the relative importance of hydrating the cysts decreased with nymphal age. Especially, the first instar and to a lesser extent the second instar appear to be susceptible to water shortage. Effects of prolonged rearing on development and reproduction on brine shrimp cysts from different origins were tested in the presence of plant material. Rearing M. pygmaeus on Artemia sp. (Jingyu Lake) cysts yielded similar survival, development, adult weight and fecundity in the fourth as in the second generation. In contrast, for Artemia franciscana cysts, an increase in nymphal development was notable. Biochemical analyses showed that total amino acid content and the concentration of the different amino acids did not differ among diets and generations. There were, however, differences in total fatty acid content between the different diets and generations and in the concentration of certain fatty acids, indicating that insects fed brine shrimp cysts may show nutritional deficiencies compared to those reared on a diet of Ephestia kuehniella eggs. Our results indicate that decapsulated brine shrimp cysts are an economically viable alternative food source in at least part of the rearing process for M. pygmaeus.     

Eggs of Ephestia kuehniella and Ceratitis capitata,and motile stages of the astigmatid mites Tyrophagus putrescentiae and Carpoglyphus lactis as factitious foods for Orius spp.

Several factitious foods were assessed for rearing the anthocorid predators Orius thripoborus (Hesse) and Orius naivashae (Poppius) (Hemiptera: Anthocoridae) in the laboratory. Developmental and reproductive traits of both Orius species were examined when offered frozen eggs of the Mediterranean flour moth, Ephestia kuehniella Zeller, frozen processed eggs of the medfly, Ceratitis capitata Wiedemann, or mixed motile stages of the astigmatid mites Tyrophagus putrescentiae (Schrank) or Carpoglyphus lactis (L). Whereas C. lactis and T. putresecentiae proved to be an inferior food for rearing O. thripoborus and O. naivashae, eggs of C. capitata fully supported development and reproduction of both predators. Results on medfly eggs were similar or slightly inferior to those on E. kuehniella eggs, which is the standard food for culturing these anthocorid bugs. O. thripoborus could be maintained for 4 consecutive generations on C. capitata eggs indicating that processed medfly eggs can be a suitable and cheaper alternative to E. kuehniella eggs for prolonged rearing of these Orius spp.     

The mating systems of three species of minute pirate bug,Orius sauteri,O. minutus,and O. strigicollis

We compared the mating systems and genital morphology of three Orius species dominant in Japan: Orius sauteri (Poppius), Orius minutus (L.), and Orius strigicollis (Poppius) (Heteroptera: Anthocoridae). In all three species, the males were polygamous and could inseminate at least three females at a rate of one female per day. Compared to the other two species, the O. minutus males had a lower rate of success in three consecutive mating orders. The mated females laid the same number of eggs irrespective of mating sequence. Orius minutus and O. strigicollis females were found to be monandrous, and they re‐mated with another male only when the 1st mating failed. In contrast, O. sauteri females were polyandrous and accepted a 2nd male even when the 1st mating was successful. Multiple mating with a single male did not increase their fecundity, and it decreased the hatching success of eggs. Mating with multiple males did not affect the fecundity or hatching success. Our scanning electron microscopy observation suggested that the genitalia of O. minutus and O. strigicollis were more similar in shape. The similarities in mating system and morphology between O. minutus and O. strigicollis support a close phylogenetic relationship.     

Variation in susceptibility and selection for resistance to imidacloprid and thiamethoxam in Mediterranean populations of Orius laevigatus

Imidacloprid and thiamethoxam are neonicotinoids that have been tested in several Orius species, including Orius laevigatus (Fieber) (Hemiptera: Anthocoridae), but not the variability in their effect among Orius populations of a single species. In this study, the variation in susceptibility to imidacloprid and thiamethoxam in 30 Mediterranean wild populations and four commercial populations of O. laevigatus was investigated in the laboratory using a standard dip bioassay method. Lethal concentration values (LC₅₀) and the mortality of adults at the maximum field rate (MFR) were calculated. The range of LC₅₀ of thiamethoxam was from 0.7 to 5.9 mg l^?1, an 8.4‐fold variability, obtaining mortality at MFR (100 mg l^?1) of >89.1% in all populations. The baseline obtained a value of 2.1 mg l^?1, which is very low compared to the MFR. For imidacloprid, the LC₅₀ varied from 7.7 to 94.7 mg l^?1 (12.3‐fold variability). Mortalities at the MFR (150 mg l^?1) were 57.7–99.2%, that is, more variable than for thiamethoxam. The LC₅₀ value of the baseline was 48.7 mg l^?1, also low compared to the MFR. This variation was exploited to select two populations resistant to thiamethoxam and imidacloprid, respectively. Artificial selection for on average 40 cycles significantly increased the resistance to thiamethoxam (LC₅₀ = 149.1 mg l^?1) and imidacloprid (LC₅₀ = 309.9 mg l^?1). Mortalities at the MFR in the thiamethoxam‐ and imidacloprid‐resistant populations were 44.5 and 36.9%, respectively. These results demonstrate that resistance can be enhanced in biocontrol agents by artificial selection under laboratory conditions, starting with populations showing no or very low tolerance. Our neonicotinoid‐resistant populations might enhance the wider adoption of biological control by allowing punctual or hotspot applications of neonicotinoids to control several main and secondary pests.     

Host rearing is a bottleneck for classical biological control of the cherry bark tortrix: A comparative analysis of artificial diets

This paper describes a comparative analysis of the suitability of three artificial diets for the development of the cherry bark tortrix (CBT), Enarmonia formosana Scopoli (Lepidoptera: Tortricidae), to simplify the rearing process for this species and its potential classical biological control agents. The three diets tested included (1) a pinto bean-based diet modified specifically for the CBT, (2) the diet for codling moth, Cydia pomonella Linnaeus (Lepidoptera: Tortricidae), and (3) the Singh general-purpose diet. Survival from first instar to the pupal stage was very low on the pinto bean, codling moth, and Singh general-purpose diets (29, 0, and 0%, respectively). Survival was consistently greater, yet still low, for larvae that were reared through the first instar on bark and subsequently transferred to the codling moth or Singh general-purpose diets (5 and 32%, respectively). In comparison, larvae started on the pinto bean diet as second instars had a survival rate of 90%, only slightly below that of sibling larvae from the cherry bark control group (100%). Larval development time was fastest on cherry bark (36±2?days), differing significantly from that on the pinto bean diet (started as first instars: 58±2?days; started as second instars: 46±2?days), but not from the development time of larvae on the Singh general-purpose diet (44±3?days). Pupal weights were greatest for specimens from the Singh general-purpose diet (14.9±0.5?mg) and lowest for those from the pinto bean diet (started as first instar: 12.3±0.6?mg; started as second instar: 12.1±0.4?mg). Pupal weights from cherry bark were intermediate (13.5±0.6?mg). Early mortality, resulting primarily from rejection of the diet, remains to be the critical impediment in CBT rearing. It is therefore suggested that a phagostimulant from cherry bark be identified and included in an artificial diet shown to be nutritionally suitable, such as the Singh general-purpose diet or the pinto bean diet.