James E. Keller

Insecticidal and nematicidal properties of microbial metabolites

SummaryMetabolites from 942 microbial isolates were screened for insecticidal and nematicidal properties. The isolates included 302 streptomycetes, 502 ‘novel’ actinomycetes including representatives of 18 genera, 28 unidentified aerobic actinomycetes, 70 fungi and 40 bacteria other than actinomycetes. When diluted 10-fold, the metabolites from 55 isolates caused nearly 100% mortality in mosquito larvae (Aedes aegypti) within 24 h. These isolates included 27 isolates ofStreptomyces, four ofActinoplanes, three isolates each ofActinomadura andStreptoverticillium, two isolates each ofMicromonospora, Bacillus andPaecilomyces, and one isolate each ofMicropolyspora, Nocardiopsis, Streptosporangium, Oerskovia, Thermomonospora, Chainia, Pseudomonas, Fusarium, Monilia andSyncephalestrum. Two fungal isolates could not be identified to the generie level. Extracts from the culture broth of 18 isolates caused 100% mortality in mosquito larvae within 15 min to 24 h at a concentration of 1000 ppm. The LC50 of partially purified products from two isolates was 1–2.5 ppm and that of the semipurified preparations from four other isolates was ≤50 ppm. Valinomycin was identified as an active component in the culture broth from one isolate. The culture broth from 15 isolates of aerobic actinomycetes and 4 of fungi were toxic toPanagrellus redivivus (Nematoda); these included 12 isolates with selective nematicidal properties.

Modification of female onion fly,Delia antiqua (Meigen), reproductive behavior by male paragonial gland extracts (Diptera: Anthomyiidae)

Egg depositional rates of onion flies, Delia antiqua(Meigen), injected thoracically with extracts of male paragonial glands were identical (14.5 eggs/female/ day) to those of normally mated females. Moreover, when continuously exposed to males, extract-injected females refused to mate and produced unfertilized eggs for the duration of the > 15- day experiment. For this normally monocoitic dipteran, <1 male equiv of paragonial secretion completely reproduced the ovipositional responses characteristic of normal mating, and this effect required no involvement of the genitalia or genital chamber. We suggest that the receptor for the active chemical (s) (sex peptide?) would be an excellent target for biorational insect control by sterilization. Moreover, these primer sex pheromones might play an important role in insect reproductive isolation and evolution.

Onion fly,Delia antiqua, oviposition and mating as influenced by insect age and dosage of male reproductive tract extract (Diptera: Anthomyiidae)

One hundred percent of virgin female onion flies,Delia antiqua, receiving ≥1/20 of a male equivalent of an aqueous extract of mature male reproductive tract remained unmated in the presence of males and began laying unfertilized eggs at a normally mated rate of about 20 eggs/female/day. The 50% behavioral response (BR50) fell between 1/40 and 1/20 of a male equivalent. Sex peptide responses are not always all-or-none. Some females receiving extract at ≤1/40 male equivalent oviposited at an intermediate rate. Moreover, at low sex peptide dosages, some females were fully activated ovipositionally but were receiptive to mating. A low level of sex peptide was present in 1-day-old males. Sex peptide titer rose with age until plateauing by 6 days posteclosion. Males began mating at 3 days, when they first had ample mature sperm; 50% of 6-day-old males mated. The mean number of females inseminated per male exposed to an excess of virgin females over 24 h was 4.3±0.6 (±SE). Presence of mature eggs was not always a prerequisite for mating, although probability of insemination was correlated with egg maturation. One-day-old preovipositional females receiving 1/20 of a male equivalent of extract began ovipositing when they had mature eggs at 5–6 days old. Therefore, sex peptide may act early and permanently or have a long half-life and affect behaviors once females reach sexual maturity. Male flies provide females with an excess of sex peptide in many cases.D. antiqua males transferred ca. 5–10 times more sex peptide than necessary to activate females fully. We suggest this excess is related to the speed of female response. It is yet unclear whether sex peptide potency or titer in Diptera has become exaggerated by intra- or intersexual selection.

Onion fly (Delia antiqua) egg depositional behaviour: pinpointing host acceptance by an insect herbivore

Abstract Egg deposition by the onion fly, Delia antiqua (Meigen), consisted of an almost completely deterministic behavioural sequence including Subsurface Probing, Egg Into Bursa, Stationary Phase, Ovipositor Contractility and Egg Expulsion. Ancillary behaviours, such as body repositioning, leg grooming and mouthpart extension, occurred during, but not between, the sequential behaviours. Stationary Phase duration (mean ± SEM = 18 ± 0 s) was less variable than the durations for other behavioural states, indicating a very precise timing mechanism associated with fertilization. Small, but significant, shortening of the ovipositor from Subsurface Probing (3.7 mm) to Egg Into Bursa (3.2 mm) to Stationary Phase (2.9 mm) suggests exact positioning of the egg for fertilization. The command to move an egg, sent during Subsurface Probing, marks the boundary between examining and consuming behaviours and appears to be associated with a switch from motor programmes generating highly probabilistic predepositional behaviour to a programme generating deterministic depositional behaviour. Onion fly egg deposition is a fixed action pattern possibly triggered by mechanosensory and/or chemosensory input received by ovipositor setae during Subsurface Probing. This deterministic depositional behaviour contrasts with the recently preceding unfixed, sensory-dependent predepositional examining behaviours. Hence, for D. antiqua , egg movement is synonymous with ovipositional host acceptance.

Effect of male accessory gland extracts on female oviposition and sexual receptivity of the Caribbean fruit fly (Diptera: Tephritidae)

ABSTRACT Anastrepha suspensa (Loew) male accessory glands do not appear to possess a sex peptide, a factor that induces oviposition or inhibits mating receptivity. Injection of accessory gland extracts from laboratory-colony males into virgin females stimulated daily deposition of only 4 eggs per female, comparable to injections of whole reproductive tract extract (5 eggs per female) and negative controls (4 to 5 eggs per female). Mated females laid significantly more (10 eggs per female per d). Studies of wild-caught males and females yielded the same information: injection of an accessory gland/testes extract or saline both elicited 8 eggs per female per d whereas normally mated females laid 16 eggs per female per d. Female receptivity to mating following injection of accessory gland or whole reproductive tract extracts was comparable to the negative control group, in which 67% to 83% of treated females remated and 63% to 89% of control females remated. In contrast, only 43% of once-mated (positive control) females remated when placed with males. Once-mated females also took significantly longer to remate after exposure to males (359 min) than females from both treatment (61 to 169 min) and negative control groups (76 to 122 min). The duration of mating was similar among all groups (24 to 37 min). These results suggest that oviposition and receptivity inhibition in A. suspensa are not mediated by male-derived humoral factors.

Specificity of accessory gland extracts in three Delia fly species (Diptera: Anthomyiidae)

Abstract. Extracts of testes and male accessory (paragonial) glands made from three species of Delia (onion fly {D.antiqua), seedcorn fly (D.platura), and cabbage fly (D.radicum)) were injected into conspecific virgin females. Extracts of paragonial glands, but not testes, from onion, seedcorn and cabbage fly males stimulated oviposition and suppressed mating when injected into conspecific virgin females. When extracts of paragonial glands from males of these species were injected into heterospecific virgin females, the extracts of D.antiqua and D.platura were fully cross‐reactive with respect to oviposition; interspecific injection stimulated oviposition at the level of the conspecific mated controls. Injection of D.radicum extract fully activated the D.antiqua and D.platura ovipositional response. D.antiqua extract caused mating inhibition and partial oviposition in D.radicum; that of D.platura had no effect on either oviposition or mating inhibition in D.radicum. These results suggest that D.antiqua and D.platura are more closely related to one another than either is to D.radicum, and agree with published anatomically‐based phylogenies and a genetic distance calculation based on eight enzyme loci. The occurrence of sex peptide cross‐reactivity, though asymmetrical, between D.radicum versus D.antiqua and D.platura indicates that, functionally, sex peptides have changed little during the evolution of this genus. An emerging pattern of broad cross‐reactivity within genera suggests that sex peptides are not an initiator of reproductive isolation.

Onion fly oviposition as influenced by soil temperature

A direct causal relationship was demonstrated between soil temperature and insect ovipositional propensity. When ovipositional substrates (soils) at 5, 15, 22, 30, 35, and 40 °C were presented in multiple treatment (‘choice’) tests with air temperature at 15 or 22 °C, onion flies, Delia antiqua (Meigen) (Diptera: Anthomyiidae), laid the most eggs in the 22 °C substrate. Only 50 eggs were laid when air temperature was increased to 30 °C, as compared to 454 and 1128 eggs at 22 and 15 °C, respectively. Thus, an air temperature of 30 °C appears to be near the upper limit of onion fly ovipositional activity. The numbers of flies observed (counts taken every 15 min) on substrates ranging from 15 to 40 °C were not significantly different. Reduced alightment/arrestment does not explain reduced oviposition on the warmer substrates; however, it may partly explain reduced oviposition on 5 °C substrates. The range of substrate temperatures facilitating substantial oviposition was narrower than that eliciting alightment/arrestment on the substrate. The ca. 20 °C ovipositional optimum corresponds well with temperatures favoring egg survival and development.